Scaled quantum mechanical force fields for trifluoromethyl selenium derivatives. I. The C[F.sub.3]SeCN and C[F.sub.3]SeC[H.sub.3] molecules.Abstract: Force fields and vibrational properties were calculated for the trifluoromethyl selenium selenium (səlē`nēəm), nonmetallic chemical element; symbol Se; at. no. 34; at. wt. 78.96; m.p. 217°C;; b.p. about 685°C;; sp. gr. 4.81 at 20°C;; valence −2, +4, or +6. derivatives derivatives In finance, contracts whose value is derived from another asset, which can include stocks, bonds, currencies, interest rates, commodities, and related indexes. Purchasers of derivatives are essentially wagering on the future performance of that asset. , C[F.sub.3]SeCN and C[F.sub.3]SeC[H.sub.3], by means of density functional theory Density functional theory (DFT) is a quantum mechanical theory used in physics and chemistry to investigate the ground state of many-body systems, in particular atoms, molecules and the condensed phases. (DFT DFT - discrete Fourier transform ) techniques. The existing experimental data and assignments for these molecules were confirmed by the theoretical results. These data were subsequently used in the definition of scaled quantum mechanical force fields for such chemical species. The obtained force constants are compared with results previously published for similar compounds. Key words: trifluoromethyl selenium, force constants, structure, DFT calculation. Resume : Faisant appel ap·pel n. Sports A quick stamp of the foot used in fencing as a feint to produce an opening. [French, from appeler, to call, from Old French apeler, to appeal; see a des techniques de la theorie de la fonctionnelle de densite Densite (den´sīt), n.pr the brand name for a form of α-hemihydrate with a low setting expansion and greater hardness; used for dies, models, and casts; sometimes referred to as a Class II stone. (<< DFT >>), on a calcule Cal´cule n. 1. Reckoning; computation. v. i. 1. To calculate les champs de force et les proprietes vibrationnelles de derives trifluoromethylselenium, soit le C[F.sub.3]SeCN et le C[F.sub.3]SeC[H.sub.3]. Les donnees experimentales et les attributions pour ces composes ont ete confirmees par les resultats theoriques. On a subsequemment utilise ces donnees dans la definition d'un champ de force normalise Verb 1. normalise - become normal or return to its normal state; "Let us hope that relations with this country will normalize soon" normalize change - undergo a change; become different in essence; losing one's or its original nature; "She changed completely en mecanique quantique pour de telles especes. On a compare les constantes de force obtenues avec les resultats publies anterieurement pour des composes semblables. Mots cles : trifluoromethylselenium, constantes de force, calculs selon la theorie de la fonctionnelle de densite. [Traduit par la Redaction] Introduction A theoretical study of the vibrational properties of the selenium compounds, C[F.sub.3]SeX (X = H, D, Cl, or Br), was recently performed in our laboratory (1). Similar calculations are now made on other two simple C[F.sub.3]Se derivatives, i.e., C[F.sub.3]SeCN and C[F.sub.3]SeC[H.sub.3]. These molecules were prepared from (C[F.sub.3]Se)2Hg by Dale et al. (2) and by Emeleus and Welchman Welch´man n. 1. See Welshman. (3). The molecular parameters for C[F.sub.3]SeCN were obtained by the electron diffraction Electron diffraction The phenomenon associated with interference processes that occur when electrons are scattered by atoms to form diffraction patterns. method (4), but no structural study is known for the C[F.sub.3]SeC[H.sub.3] molecule. IR and Raman Ra·man , Sir Chandrasekhara Venkata 1888-1970. Indian physicist. He won a 1930 Nobel Prize for his discovery of the Raman effect. spectra were reported for these two molecules by Marsden Marsden is both a surname and a place name. As a surname As a surname, Marsden may refer to:
In the present work, quantum chemical calculations were performed on the mentioned molecules to obtain the corresponding force constants, which were scaled to reproduce re·pro·duce v. 1. To produce a counterpart, an image, or a copy of something. 2. To bring something to mind again. 3. To generate offspring by sexual or asexual means. the experimental frequencies. Such adjustment was made using the formalism Formalism or Russian Formalism Russian school of literary criticism that flourished from 1914 to 1928. Making use of the linguistic theories of Ferdinand de Saussure, Formalists were concerned with what technical devices make a literary text literary, apart of the scaled quantum mechanical (SQM SQM Square Meters SQM Software Quality Management SQM Sky Quality Meter SQM Service Quality Management SQM Signal Quality Monitoring SQM Stable Queue Manager SQM Surface Quality Monitor SQM Supplier Quality Manual SQM Signal Quality Monitor ) force field, as defined by Pulay et al. (8). Calculation procedure Optimized structures and vibrational wavenumbers for C[F.sub.3]SeCN and C[F.sub.3]SeC[H.sub.3] were obtained with density functional theory (DFT) methods using the B3LYP LYP Local Yellow Pages (directory advertising) functional (9, 10) together with the 6-311[G.sup.*] basis set. This theoretical data facilitated the comparison of the results with those obtained in previous work in which the same combination of functional and basis sets was used. The natural bond orbitals orbitals (ōrˑ·b  ·t (NBO NBO Natural Bond OrbitalNBO Network Byte Order (TCP/IP) NBO New Business Opportunity NBO Novell Branch Office (business office management solution) NBO Neighborhood Box Office, Inc. ) formalism (11) was used for the calculation of the atomic charges, which appear in Fig. 1. The calculations were made with the Gaussian 98 set of programs (12). [FIGURE 1 OMITTED] Structural results The molecular conformations of the two molecules were investigated starting with initial, staggered structures having FCSeC dihedral di·he·dral adj. Mathematics 1. Formed by or having two plane faces; two-sided. 2. Relating to, having, or forming a dihedral angle. n. 1. Mathematics a. A dihedral angle. angles of 180[degrees]. The respective C[F.sub.3] group was rotated rotated turned around; pivoted. rotated tibia see rotated tibia. around the Se-C bond from 0[degrees] to 60[degrees], in steps of 5[degrees], and the structure was optimized with that dihedral angle frozen. These calculations showed that only a single conformer exists for both compounds, corresponding to the structures of symmetry symmetry, generally speaking, a balance or correspondence between various parts of an object; the term symmetry is used both in the arts and in the sciences. Cs shown in Fig. 1. The potential energy curve shows maxima for structures in which the trifluoromethyl group is rotated 60[degrees] with respect to the most stable conformation con·for·ma·tion n. One of the spatial arrangements of atoms in a molecule that can come about through free rotation of the atoms about a single chemical bond. . An additional series of calculations were performed for the C[F.sub.3]SeC[H.sub.3] molecule in which the C[F.sub.3] and C[H.sub.3] groups were rotated simultaneously in the same or opposite directions in steps of 10[degrees]. These calculations confirmed the existence of only one minimum in the potential energy surface. The most stable conformations predicted for these molecules were fully optimized, and their structures are shown in Fig. 1. As mentioned before, structural geometrical parameters were reported only for C[F.sub.3]SeCN (4), and these values are shown in Table 1 together with the calculated values. The (mean) calculated and experimental distances and angles do not differ by more than 0.020 [Ansgtrom] and 3.4[degrees], respectively. The theoretical tilt angles existing between the C-Se bonds and the ideal symmetry axis of the the diameter of the sphere which is perpendicular to the plane of the circle. See also: Axis CX3 group, with X = F or H, also appear in Table 1; this angle is calculated for the C[F.sub.3] groups as 1/3[2[alpha]([F.sub.3],4-C-Se) - 2[alpha](F2-C-Se)] (13). Clearly, C[F.sub.3]SeCN shows a tilt angle Noun 1. tilt angle - the angle a rocket makes with the vertical as it curves along its trajectory angle - the space between two lines or planes that intersect; the inclination of one line to another; measured in degrees or radians that is considerably larger than those calculated for SeC[F.sub.3] and SeC[H.sub.3] in C[F.sub.3]SeC[H.sub.3]. This theoretical result could be explained by taking into account the calculated electric charges on the atoms. In fact, the [F.sub.3], F4, and N7 atoms of C[F.sub.3]SeCN (Fig. 1) show negative charges of -0.34 (F) and -0.29 (N); whereas, in C[F.sub.3]SeC[H.sub.3] the charges are positive for H8 and H9 (+0.21) and negative for [F.sub.3] and F4 (-0.36). Therefore, the repulsive re·pul·sive adj. 1. Causing repugnance or aversion; disgusting. See Synonyms at offensive. 2. Tending to repel or drive off. 3. Physics Opposing in direction: a repulsive force. forces between the F and N atoms in the former molecule could explain the relatively large tilt angle of the SeC[F.sub.3] moiety moiety: see clan. and the predicted value of 176.6[degrees] for the Se-C-N angle; whereas, the attractive forces between the mentioned H and F atoms in the latter molecule could be the cause of the notably smaller calculated tilt angles. Vibrational results The normal modes of vibration of the C[F.sub.3]SeCN and C[F.sub.3]SeC[H.sub.3] molecules, with Cs symmetry, are classified as 10A' + 5A" and 13A' + 8A", respectively. The atomic displacements calculated for each vibrational mode, represented graphically with the program Moldraw (14), confirmed the assignment of bands proposed by Clase et al. (6) for both molecules. In fact, these authors corrected and completed a previous study made on C[F.sub.3]SeCN and related molecules by Marsden (5). The experimental wave-numbers for each molecule reported in ref. 6 appear in Tables 2 and 3 together with the corresponding qualitative intensities. In most cases, the observed values agree with the calculated IR and Raman band intensities. That agreement is particularly clear for the bands due to the C[F.sub.3] stretching vibrations where the strongly polarized A one-way direction of a signal or the molecules within a material pointing in one direction. C-F bonds produce very strong IR bands and weak or very weak Raman bands. The agreement between measured and calculated wavenumbers was evaluated by means of the root-mean-square deviation (RMSD), which was equal to 29 [cm.sup.-1] for C[F.sub.3]SeCN and 55 [cm.sup.-1] for C[F.sub.3]SeC[H.sub.3]. After the force field scaling procedure, these values fell to 8 and 7 [cm.sup.-1], respectively. Force constants The force fields in Cartesian coordinates Cartesian coordinates (kärtē`zhən) [for René Descartes], system for representing the relative positions of points in a plane or in space. , as generated by the Gaussian programs for the two molecules, were transformed to the set of non-redundant coordinates defined in Tables 4 and 5. Such coordinates consider the local symmetry In physics, a symmetry describes a quality of a physical system that is independent upon modifying variables that describe that system (one says that the theory is invariant under such transformations). of the C[F.sub.3] and C[H.sub.3] groups and follow the proposals of Fogarasi et al. (15). The resulting force constants were subsequently scaled according to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. the scheme of Pulay et al. (8), in which the main force constants are multiplied by scale factors (e.g., [f.sub.i] and [f.sub.j]), and the corresponding interaction constants are multiplied by [([f.sub.i] x [f.sub.j]).sup.1/2], adjusting the scale factors to reproduce the experimental wavenumbers as accurately as possible. The final scaling factors corresponding to each force constant for the two studied species appear in Table 6. Obviously, most of these factors are greater than one. This is the case when heavy atoms (after the second row of the Periodic Table) appear in the molecule. This fact has been reported for many molecules containing non-metallic heavy atoms (16) as well as for several C[F.sub.3]S[O.sub.2]X molecules (17). To prove that the scaling factors are transferable between related molecules, a subsequent calculation was performed using the mean factors for common coordinates previously obtained for the C[F.sub.3]SeX series (1) and adjusting only the factors that affect the non-common coordinates. In that calculation, the final RMSD values did not differ by more than 1 [cm.sup.-1] from those obtained with the scaling factors of Table 6. The main force constants in symmetry coordinates as well as some interaction constants for the studied molecules are reproduced in Tables 7 and 8 together with the corresponding values calculated by Wahi et al. (7). Clearly, no large differences appear between both sets of main force constants, based in the same vibrational band assignments. However, there are significant disagreements between the sets of interaction constants, probably because most of these values were fixed in the traditional procedure of refinement performed by these authors. On the other hand, the theoretical approach used in the present work produces a complete force constants matrix. The SQM matrices are available as supplementary data. (3) The SQM force fields were used to calculate the potential energy distributions (PED n. 1. A basket; a hammer; a pannier. ) that appear in Tables 2 and 3. The PED show that some coordinates are strongly mixed in both molecules, as is the case with S3 (v(C[F.sub.3]) symm.), [S.sub.4] ([delta](C[F.sub.3]) symm.), and [S.sub.8] (v(C-Se)) for C[F.sub.3]SeCN and the corresponding [S.sub.6], [S.sub.8], and [S.sub.11] coordinates for C[F.sub.3]SeC[H.sub.3], which appear to be contributing in different proportions to the modes [v.sub.3] and [v.sub.4] for the first molecule and [v.sub.6] and [v.sub.8] for the latter. A similar observation was made for the C[F.sub.3]SeX molecules (1). The internal force constants calculated from the corresponding SQM force fields for these molecules are shown in Table 9. As expected, these force constants are close to the values previously obtained for other selenium derivates using the same calculation procedure (1). Acknowledgements Research grants from the following institutions in R. Argentina Argentina (ärjəntē`nə, Span. ärhāntē`nä), officially Argentine Republic, republic (2005 est. pop. 39,538,000), 1,072,157 sq mi (2,776,889 sq km), S South America. are gratefully acknowledged: CONICET CONICET Consejo Nacional de Investigaciones Científicas Y Técnicas (National Council for Science and Technology, Argentina) (Consejo Consejo is a village in the north of Corozal District of the nation of Belize. Consejo is located on a point of land where the bays of Corozal and Chetumal meet. Consejo is about 8 miles from the district capital of Corozal Town, and two miles, across the water, from Nacional Nacional is the Spanish and Portuguese word for national. It can refer to: Sports
UNLP United Nations License Plate (Universidad Universidad (English: University) may refer to:
See San Miguel de Tucuman. ). We thank Dr. G. Arteca, Laurentian University Laurentian University, main campus at Sudbury, Ont., Canada; bilingual, coeducational; founded 1960. Among its faculties are those in astronomy, commerce, computer science, education, engineering, law, mathematics, music, native studies, nursing, physics, and social , Canada Canada (kăn`ədə), independent nation (2001 pop. 30,007,094), 3,851,787 sq mi (9,976,128 sq km), N North America. Canada occupies all of North America N of the United States (and E of Alaska) except for Greenland and the French islands of , for providing access to some published articles. (3) Supplementary data for this article are available on the journal Web site or may be purchased from the Depository The place where a deposit is placed and kept, e.g., a bank, savings and loan institution, credit union, or trust company. A place where something is deposited or stored as for safekeeping or convenience, e.g., a safety deposit box. of Unpublished Data, Document Delivery, CISTI CISTI Canada Institute for Scientific and Technical Information CISTI Civil Space Technology Initiative CISTI Canadian Institute of Telecommunications Engineers , National Research Council Canada, Ottawa Ottawa, city, Canada Ottawa (ŏt`əwə), city (1991 pop. 313,987), capital of Canada, SE Ont., at the confluence of the Ottawa and Rideau rivers. Hull, Que. , ON K1A 0S2, Canada. DUD 5112. For more information on obtaining material, refer to http://cisti-icist.nrc-cnrc.gc.ca/irm/unpub_e.shtml. References (1.) L.E. Fernandez and E.L. Varetti. J. Mol. Struct.: THEOCHEM, 761, 217 (2006). (2.) J.W. Dale, H.J. Emeleus, and R.N. Haszeldine. J. Chem. Soc. 2939 (1958). (3.) H J. Emeleus and N. Welchman. J. Chem. Soc. 1268 (1963). (4.) C.J. Marsden and G.M. Sheldrick. J. Mol. Struct. 10, 413 (1971). (5.) C.J. Marsden. J. Fluorine fluorine (fl  `ərēn, –rĭn), gaseous chemical element; symbol F; at. no. 9; at. wt. 18.998403; m.p. −219.6°C;; b.p. −188.14°C;; density 1. Chem. 5, 401 (1975).
(6.) H.J. Clase, P.K. Wahi, and D.R.L. Bomford. Can. J. Spectrosc. 22, 92 (1977). (7.) P.K. Wahi and N.D. Patel. Can. J. Spectrosc. 22, 88 (1977). (8.) P. Pulay, G. Fogarasi, G. Pongor, J.E. Boggs Boggs is a surname, and may refer to:
(9.) A.D. Becke. J. Chem. Phys. 98, 5648 (1993). (10.) C. Lee, W. Yang yang (yang) [Chinese] in Chinese philosophy, the active, positive, masculine principle that is complementary to yin; see yin, under principle. , and R.G. Parr. Phys. Rev. B, 37, 785 (1988). (11.) A.E. Reed, L.A. Curtiss, and F. Weinhold. Chem. Rev. 88, 899 (1988). (12.) M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery, Jr., R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J.Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe, P.M.W. Gill gill, in weights and measures gill, in weights and measures: see English units of measurement. , B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez, Head-M. Gordon, E.S. Replogle, and J.A. Pople. GAUSSIAN 98 [computer program]. Revision a.7. Gaussian, Inc., Pittsburgh, PA. 1998. (13.) J.S. Francisco. Spectrochim. Acta, 40A, 923 (1984). (14.) P. Ugliengo, D. Viterbo, and G. Chiari. Z. Kristallogr. 207, 9 (1993). (15.) G. Fogarasi, X. Zhou, P.W. Taylor, and P. Pulay. J. Am. Chem. Soc. 114, 8191 (1992). (16.) F. Kalincsak and G. Pongor. Spectrochim. Acta, 58A, 999 (2002). (17.) L.E. Fernandez, A. Ben Altabef, and E.L. Varetti. J. Mol. Struct. 612, 1 (2002). L.E. Fernandez. Instituto de Quimica y Fisica, Facultad de Bioquimica, Quimica y Farmacia, Universidad, Nacional de Tucuman, San Lorenzo San Lorenzo, town, S Honduras, on the Gulf of Fonseca. Its satellite, Henecán is the chief Pacific port of Honduras. Henecán's modern port facilities and deepwater harbor and channel approach were constructed in the late 1970s after the old port at 456, 4000 S.M. de Tucuman, Republica Argentina. E.L. Varetti. (1,2) Centro de Quimica Inorganica (CEQUINOR, CONICET-UNLP), Departamento de Quimica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C. Correo 962, 1900 La Plata, Republica Argentina. (1) Member of the Carrera del Investigador Cientifico, CONICET, Republica Argentina. (2) Corresponding author (e-mail: varetti@quimica.unlp.edu.ar). Received 4 September 2006. Accepted 7 November 2006. Published on the NRC NRC abbr. 1. National Research Council 2. Nuclear Regulatory Commission Noun 1. NRC - an independent federal agency created in 1974 to license and regulate nuclear power plants Research Press Web site at http://canjchem.nrc.ca on 13 December 2006.
Table 1. Optimized geometric parameters for the molecules
C[F.sub.3]SeCN and C[F.sub.3]SeC[H.sub.3] and experimental data for
C[F.sub.3]SeCN.
C[F.sub.3]SeCN
Calculated Experimental (4)
Bond lengths ([Angstrom])
C1-F2 1.339 1.332
C1-F3,4 1.33
Se-C[F.sub.3] 2.004 1.984
Se-CN 1.846 1.854
C[equivalent to]N 1.157 1.152
Se-C[H.sub.3] -- --
C6-H7 -- --
C6-H8,9 -- --
Bond angles ([degrees])
F3-C1-F4 108.6 109.4
F2-C1-F3,4 109.1
F2-C1-Se5 105.6 109.6
F3,4-C1-Se5 112.2
Tilt Se-C[F.sub.3] 4.37 --
C-Se-C 95.6 92.2
Se-C-N 176.6 180.0 (fixed)
H8-C6-H9 -- --
H7-C6-H8,9 -- --
H7-C6-Se5 -- --
H8,9-C6-Se5 -- --
Tilt Se-C[H.sub.3] -- --
C[F.sub.3]SeC[H.sub.3]
Calculated
Bond lengths ([Angstrom])
C1-F2 1.342
C1-F3,4 1.346
Se-C[F.sub.3] 1.968
Se-CN --
C[equivalent to]N --
Se-C[H.sub.3] 1.971
C6-H7 1.089
C6-H8,9 1.087
Bond angles ([degrees])
F3-C1-F4 106.7
F2-C1-F3,4 108.1
F2-C1-Se5 108.7
F3,4-C1-Se5 112.6
Tilt Se-C[F.sub.3] 2.62
C-Se-C 95.4
Se-C-N --
H8-C6-H9 111.1
H7-C6-H8,9 109.8
H7-C6-Se5 106.1
H8,9-C6-Se5 110.0
Tilt Se-C[H.sub.3] 2.55
Table 2. Experimental and calculated wavenumbers, IR and Raman
intensities and, potential energy distribution (PED) for
C[F.sub.3]SeCN.
Mode Experimental (6) (a) Calcd. (b) Calcd.
SQM (c)
A'
[[nu].sub.1] 2178 (s) 2274 2185
[[nu].sub.2] 1201 vs. (vvw) 1190 1196
[[nu].sub.3] 1103 vs. (vw) 1079 1090
[[nu].sub.4] 747 vs. (vs) 742 752
[[nu].sub.5] 543 (m) 551 553
[[nu].sub.6] 534 s (m) 534 536
[[nu].sub.7] 390 m (vvw) 402 397
[[nu].sub.8] 315 m (vs) 300 316
[[nu].sub.9] 272 vw (m) 267 267
[[nu].sub.10] 118 (m) 98 97
A"
[[nu].sub.11] 1197 vs 1199 1205
[[nu].sub.12] -- 529 532
[[nu].sub.13] 356 w (vvw) 359 344
[[nu].sub.14] 282 (vvw) 273 275
[[nu].sub.15] -- 33 34
RMSD ([cm.sup.-1]) 29 8
Mode IR intensity Raman intensity
(km [mol.sup.-1]) ([[Angstrom].sup.4]
[(amu).sup.-1])
A'
[[nu].sub.1] 2.14 109.75
[[nu].sub.2] 225.92 0.73
[[nu].sub.3] 523.6 5.89
[[nu].sub.4] 32.83 6.79
[[nu].sub.5] 1.14 0.77
[[nu].sub.6] 3.08 3.38
[[nu].sub.7] 2.46 0.94
[[nu].sub.8] 1.1 6.86
[[nu].sub.9] 0.57 3.01
[[nu].sub.10] 3.77 3.29
A"
[[nu].sub.11] 270.59 0.61
[[nu].sub.12] 1.44 0.99
[[nu].sub.13] 1.35 1.88
[[nu].sub.14] 0.03 1.16
[[nu].sub.15] 1.49 1.24
RMSD ([cm.sup.-1])
Mode PED
(contributions [greater than or equal to] 10%)
A'
[[nu].sub.1] 95 [S.sub.1]
[[nu].sub.2] 101 [S.sub.2] + [S.sub.5]
[[nu].sub.3] 76 [S.sub.3] + [S.sub.4] + 22 [S.sub.8]
[[nu].sub.4] 47 [S.sub.4] + 31 [S.sub.3] + 14 [S.sub.8]
[[nu].sub.5] 50 [S.sub.5] + 22 [S.sub.6]
[[nu].sub.6] 72 [S.sub.6] + 19 [S.sub.5]
[[nu].sub.7] 37 [S.sub.7] + [S.sub.5] + 24 [S.sub.10]
[[nu].sub.8] 66 [S.sub.8] + 11 S4
[[nu].sub.9] 84 [S.sub.9] + 23 [S.sub.7]
[[nu].sub.10] 78 [S.sub.10] + 32 [S.sub.7] + 19 [S.sub.9]
A"
[[nu].sub.11] 102 [S.sub.11] + 18 [S.sub.12]
[[nu].sub.12] 77 [S.sub.12]
[[nu].sub.13] 98 [S.sub.13]
[[nu].sub.14] 96 [S.sub.14] + 11 [S.sub.12]
[[nu].sub.15] 103 [S.sub.15]
RMSD ([cm.sup.-1])
Mode Main coordinate
A'
[[nu].sub.1] [nu](C[equivalent to]N)
[[nu].sub.2] [nu](C[F.sub.3]) antisymm.
[[nu].sub.3] [nu](C[F.sub.3]) symm.
[[nu].sub.4] [delta](C[F.sub.3]) symm.
[[nu].sub.5] [delta](C[F.sub.3]) antisymm.
[[nu].sub.6] [nu](Se-C(N))
[[nu].sub.7] [delta](SeCN) in plane
[[nu].sub.8] [nu](([F.sub.3])C-Se)
[[nu].sub.9] [rho](C[F.sub.3])
[[nu].sub.10] [delta](CSeC)
A"
[[nu].sub.11] [nu](C[F.sub.3]) antisymm.
[[nu].sub.12] [delta](C[F.sub.3]) antisymm.
[[nu].sub.13] [delta](SeCN) out of plane
[[nu].sub.14] [rho](C[F.sub.3])
[[nu].sub.15] Torsion (C[F.sub.3])
RMSD ([cm.sup.-1])
(a) Qualitative intensities for IR and Raman (in parentheses)
observed bands: w, weak; m, medium; s, strong; v, very.
(b) B3LYP/6-311G* calculations.
(c) From SQM force field.
Table 3. Experimental and calculated wavenumbers, IR and Raman
intensities, and potential energy distribution (PED) for
C[F.sub.3]SeC[H.sub.3].
Mode Experimental (6) (a) Calcd. (b) Calcd.
SQM (c)
A'
[[nu].sub.1] 3035 w (w) 3161 3039
[[nu].sub.2] 2955 s (s) 3069 2950
[[nu].sub.3] 1438 s 1497 1440
[[nu].sub.4] 1288 vs 1337 1284
[[nu].sub.5] 1157 vs 1161 1167
[[nu].sub.6] 1117 vs (vw) 1097 1106
[[nu].sub.7] 916 939 903
[[nu].sub.8] 740 vs (s) 735 742
[[nu].sub.9] 597 577 599
[[nu].sub.10] 533 w (vw) 538 541
[[nu].sub.11] 339 s (ms) 331 338
[[nu].sub.12] 302 m (m) 295 298
[[nu].sub.13] 148 (m) 156 150
A"
[[nu].sub.14] 3036 w (w) 3172 3050
[[nu].sub.15] 1431 s (vw) 1484 1427
[[nu].sub.16] 1141 vs 1133 1140
[[nu].sub.17] 911 934 897
[[nu].sub.18] 536 526 529
[[nu].sub.9] 289 (w) 283 285
[[nu].sub.20] -- 129 129
[[nu].sub.21] -- 51 49
RMSD ([cm.sup.-1]) 55 7
Mode IR intensity Raman intensity
(km [mol.sup.-1]) ([[Angstrom].sup.4]
[(amu).sup.-1])
A'
[[nu].sub.1] 3.38 56.62
[[nu].sub.2] 13.33 113.22
[[nu].sub.3] 12.32 7.81
[[nu].sub.4] 11.39 0.36
[[nu].sub.5] 241.27 0.8
[[nu].sub.6] 438.34 1.28
[[nu].sub.7] 17.36 3.76
[[nu].sub.8] 15.64 4.29
[[nu].sub.9] 0.68 20.64
[[nu].sub.10] 0.29 1.22
[[nu].sub.11] 2.15 4.12
[[nu].sub.12] 0.6 3.41
[[nu].sub.13] 1.82 1.28
A"
[[nu].sub.14] 3.38 56.62
[[nu].sub.15] 6.31 10.49
[[nu].sub.16] 263.8 0.7
[[nu].sub.17] 4.63 3.43
[[nu].sub.18] 0.55 0.95
[[nu].sub.9] 0 1.19
[[nu].sub.20] 0.04 0.03
[[nu].sub.21] 0.87 1.17
RMSD ([cm.sup.-1])
Mode PED
(contributions [greater than or equal to] 10%)
A'
[[nu].sub.1] 100 [S.sub.1]
[[nu].sub.2] 100 [S.sub.2]
[[nu].sub.3] 96 [S.sub.3]
[[nu].sub.4] 105 [S.sub.4]
[[nu].sub.5] 96 [S.sub.5] + 18 [S.sub.10]
[[nu].sub.6] 70 [S.sub.6] + 49 [S.sub.8] + 24 [S.sub.11]
[[nu].sub.7] 88 [S.sub.7]
[[nu].sub.8] 42 [S.sub.8] + 35 [S.sub.6] + 12 [S.sub.11]
[[nu].sub.9] 107 [S.sub.9]
[[nu].sub.10] 73 [S.sub.10]
[[nu].sub.11] 53 [S.sub.11] + 13 [S.sub.8] + 11 [S.sub.12]
[[nu].sub.12] 61 [S.sub.12] + 18 [S.sub.11] + 11 [S.sub.10]
[[nu].sub.13] 95 [S.sub.13] + 33 [S.sub.12]
A"
[[nu].sub.14] 100 [S.sub.14]
[[nu].sub.15] 95 [s.sub.15]
[[nu].sub.16] 100 [s.sub.16] + 19 [S.sub.18]
[[nu].sub.17] 95 [S.sub.17]
[[nu].sub.18] 73 [s.sub.18]
[[nu].sub.9] 94 [S.sub.19] + 13 [S.sub.18]
[[nu].sub.20] 108 [S.sub.20]
[[nu].sub.21] 106 [s.sub.21]
RMSD ([cm.sup.-1])
Mode Main coordinate
A'
[[nu].sub.1] [nu](C[H.sub.3]) antisymm.
[[nu].sub.2] [nu](C[H.sub.3]) symm.
[[nu].sub.3] [delta](C[H.sub.3]) antisymm.
[[nu].sub.4] [delta](C[H.sub.3]) symm.
[[nu].sub.5] [nu](C[F.sub.3]) antisymm.
[[nu].sub.6] [nu](C[F.sub.3]) symm.
[[nu].sub.7] [rho](C[H.sub.3])
[[nu].sub.8] [delta](C[F.sub.3]) antisymm.
[[nu].sub.9] [nu](Se-C[H.sub.3])
[[nu].sub.10] [delta](C[F.sub.3]) antisymm.
[[nu].sub.11] [nu](Se-C[F.sub.3])
[[nu].sub.12] [rho](C[F.sub.3])
[[nu].sub.13] [delta](CSeC)
A"
[[nu].sub.14] [nu](C[H.sub.3]) antisymm.
[[nu].sub.15] [delta](C[H.sub.3]) antisymm.
[[nu].sub.16] [nu](C[F.sub.3]) antisymm.
[[nu].sub.17] [rho](C[H.sub.3])
[[nu].sub.18] [delta](C[F.sub.3]) antisymm.
[[nu].sub.9] [rho](C[F.sub.3])
[[nu].sub.20] Torsion (C[H.sub.3])
[[nu].sub.21] Torsion (C[F.sub.3])
RMSD ([cm.sup.-1])
(a) Qualitative intensities for IR and Raman (in parentheses)
observed bands: w, weak; m, medium; s, strong; v, very.
(b) B3LYP/6-311G* calculations.
(c) From SQM force field.
Table 4. Natural internal (local symmetry) coordinates for
C[F.sub.3]SeCN.
Definition (according to Fig. 1) Description (a)
A'
[S.sub.1] = d(6-7) [nu](C[equivalent to]N)
[S.sub.2] = 2r(1-2) - r(1-3) - r(1-4) [nu](C[F.sub.3]) antisymm.
[S.sub.3] = r(1-2) + r(1-3) + r(1-4) [nu](C[F.sub.3]) symm.
[S.sub.4] = [alpha](2-1-3) + [delta](C[F.sub.3]) symm.
[alpha](2-1-4) + [alpha](3-1-4) -
[beta](2-1-5) - [beta](3-1-5) -
[beta](4-1-5)
[S.sub.5] = 2[alpha](3-1-4) - [delta](C[F.sub.3]) antisymm.
[alpha](2-1-3) - [alpha](2-1-4)
[S.sub.6] = l(5-6) [nu](Se-CN)
[S.sub.7] = [delta](5-6-7) [delta](SeCN) in plane
[S.sub.8] = t(1-5) [nu](Se-C[F.sub.3])
[S.sub.9] = 2[beta](2-1-5) - [rho](C[F.sub.3])
[beta](3-1-5) - [beta](4-1-5)
[S.sub.10] = [gamma](1-5-6) [delta](CSeC)
A"
[S.sub.11] = r(1-3) - r(1-4) [nu](C[F.sub.3]) antisymm.
[S.sub.12] = [alpha](2-1-3) - [delta](C[F.sub.3]) antisymm.
[alpha](2-1-4)
[S.sub.13] = [delta](5-6-7) [delta](SeCN) out of plane
[S.sub.14] = [beta](3-1-5) - [rho](C[F.sub.3])
[beta](4-1-5)
[S.sub.15] = [SIGMA][tau] Torsion (C[F.sub.3])
[Fi-C1-Sbe5-C6)]
(a) [nu], stretching; [delta], deformation; [rho], rocking.
Table 5. Natural internal (local symmetry) coordinates for CF3SeCH3.
Definition (according to Fig. 1) Description (a)
A'
[S.sub.1] = 2d(7-6) - d(8-6) - d(9-6) [nu](C[H.sub.3]) antisymm.
[S.sub.2] = d(7-6) + d(8-6) + d(9-6) [nu](C[H.sub.3]) symm.
[S.sub.3] = 2[psi](8-6-9) - [delta](C[H.sub.3]) antisymm.
[psi](8-6-7) - [psi](9-6-7)
[S.sub.4] = [psi](7-6-9) + [delta](C[H.sub.3]) symm.
[psi](7-6-8) + [psi](8-6-9) -
[phi](7-6-5) - [phi](8-6-5) -
[phi](9-6-5)
[S.sub.5] = 2r(1-2) - r(1-3) - r(1-4) [nu](C[F.sub.3]) antisymm.
[S.sub.6] = r(1-2) + r(1-3) + r(1-4) [nu](C[F.sub.3]) symm.
[S.sub.7] = 2[phi](7-6-5) - [rho](C[H.sub.3])
[phi](8-6-5) - [phi](9-6-5)
[S.sub.8] = [alpha](2-1-3) + [delta](C[F.sub.3]) symm.
[alpha](4-1-2) + [alpha](4-1-3) -
[beta](2-1-5) - [beta](3-1-5) -
[beta](4-1-5)
[S.sub.9] = l(6-5) [nu](Se-C[H.sub.3])
[S.sub.10] = 2[alpha](3-1-4) - [delta](C[F.sub.3]) antisymm.
[alpha](3-1-2) - [alpha](4-1-2)
[S.sub.11] = t(1-5) [nu](Se-C[F.sub.3])
[S.sub.12] = 2[beta](2-1-5) - [rho](C[F.sub.3])
[beta](3-1-5) - [beta](4-1-5)
[S.sub.13] = [beta](1-5-6) [delta](CSeC)
A"
[S.sub.14] = d(8-6) - d(9-6) [nu](C[H.sub.3]) antisymm.
[S.sub.15] = [psi](8-6-7) - [delta](C[H.sub.3]) antisymm.
[psi](9-6-7)
[S.sub.16] = r(1-3) - r(1-4) [nu](C[F.sub.3]) antisymm.
[S.sub.17] = [phi](8-6-5) - [rho](C[H.sub.3])
[phi](9-6-5)
[S.sub.18] = [alpha](3-1-2) - [delta](C[F.sub.3]) antisymm.
[alpha](4-1-2)
[S.sub.19] = [beta](3-1-5) - [rho](C[F.sub.3])
[beta](4-1-5)
[S.sub.20] = [SIGMA][tau] Torsion (C[H.sub.3])
[Hi-C6-[S.sub.e5-C1)]
[S.sub.21] = [SIGMA][tau][Fi-C1- Torsion (C[F.sub.3])
[S.sub.e5-C6)]
(a) [nu], stretching; [delta], deformation; [rho], rocking.
Table 6. Final scaling factors for the force field of the molecules
C[F.sub.3]SeCN and C[F.sub.3]SeC[H.sub.3].
Coordinates (a) C[F.sub.3]SeCN C[F.sub.3]SeC
[H.sub.3]
[nu](C[F.sub.3]), 1.011 1.013
[delta](C[F.sub.3]),
[rho](C[F.sub.3]), Torsion
(C[F.sub.3])
[nu](Se-CN) 1.011 --
[nu](Se-C[H.sub.3]) -- 1.075
[nu](Se-C[F.sub.3]) 1.155 1.075
[nu](C[H.sub.3]), -- 0.924
[delta](C[H.sub.3]),
[rho](C[H.sub.3])
[delta](CSeC) 1.011 0.924
[nu](C[equivalent to]N), 0.919 --
[delta](SeCN)
Torsion (C[H.sub.3]) -- 1.013
(a) [nu], stretching; [delta], deformation; [rho], rocking.
Table 7. Symmetry force constants for the molecule
CF3SeCN.
Force constant (a) This work Reference (7)
F1,1 17.321 16.982
F2,2 5.348 5.259
F3,3 7.833 7.461
F4,4 1.639 1.733
F5,5 1.518 1.584
F6,6 3.526 3.452
F7,7 0.24 0.332
F8,8 2.583 2.482
F9,9 0.884 0.83
F10,10 0.973 0.828
F11,11 5.416 5.259
F12,12 1.454 1.584
F13,13 0.311 0.332
F14,14 0.85 0.83
F15,15 0.012 --
F3,8 0.675 0.393
F4,8 -0.437 -0.434
F5,6 -0.016 0.061
F3,4 0.64 0.65
F2,5 -0.63 -0.5
F1,7 0.021 -0.5
F2,9 0.547 0.5
F1,11 0 0.5
(a) Units are mdyn [[Angstrom].sup.-1] (1 dyn = 10 [micro]N) for
stretchings and stretch-stretch interactions, mdyn [Angstrom] for
bend and bend-bend interactions, and mdyn for strech-bend interactions.
Table 8. Symmetry force constants for the
molecule C[F.sub.3]SeC[H.sub.3].
Force constant (a) This work Reference (7)
F1,1 4.96 4.9
F2,2 5.057 4.834
F3,3 0.519 0.514
F4,4 0.527 0.588
F5,5 5.103 4.83
F6,6 7.471 7.461
F7,7 0.546 0.58
F8,8 1.633 1.792
F9,9 2.746 2.642
F10,10 1.574 1.549
F11,11 2.742 2.714
F12,12 0.9 0.93
F13,13 0.916 0.663
F14,14 4.976 4.9
F15,15 0.507 0.514
F6,11 0.628 0.221
F8,11 -0.405 -0.566
F6,8 0.655 0.65
F5,10 -0.645 -0.5
F2,1 -0.014 -0.5
F5,12 0.514 0.5
F2,4 0.13 0.5
F9,4 -0.35 -0.261
F1,3 -0.135 -0.041
F16,15 -0.011 -0.041
F16,16 4.898 4.83
F17,17 0.545 0.58
F18,18 1.502 1.549
F19,19 0.905 0.93
F20,20 0.011 --
F21,21 0.017 --
(a) Units are mdyn [[Angstrom].sup.-1] (1 dyn = 10 [micro]N) for
stretchings and stretch-stretch interactions, mdyn [Angstrom]
for bend and bend-bend interactions, and mdyn for
strech-bend interactions.
Table 9. Internal force constants for C[F.sub.3]SeCN,
C[F.sub.3]SeC[H.sub.3], and the related molecules C[F.sub.3]SeX.
This work
Force constant (a) C[F.sub.3]SeCN C[F.sub.3]SeC[H.sub.3]
Bond stretchings
f (C-F) (b) 6.167 5.841
f (Se-C[F.sub.3]) 2.583 2.742
f (Se-CN) 3.526 --
f (C[equivalent to]N) 17.321 --
f (Se-C[H.sub.3]) -- 2.746
f (C-H) (b) -- 4.996
f (C-F/C-F) (b) 0.802 0.789
f (C-F/Se-C[F.sub.3]) 0.39 0.362
f (C-H/CH) (b) -- 0.032
f (Se-CN/CN) 0.199 --
Deformations
f (F-C-F) (b) 1.269 1.304
f (F-C-Se) (b) 0.854 0.874
f (C-Se-C) 0.973 0.916
f (Se-C[equivalent to]N) 0.24 --
f (H-C-H) (b) -- 0.431
f (H-C-Se) (b) -- 0.452
Reference (1)
Force constant (a) C[F.sub.3]SeH C[F.sub.3]SeD
Bond stretchings
f (C-F) (b) 5.928 6.004
f (Se-C[F.sub.3]) 2.8 2.84
f (Se-CN)
f (C[equivalent to]N)
f (Se-C[H.sub.3])
f (C-H) (b)
f (C-F/C-F) (b) 0.826 0.844
f (C-F/Se-C[F.sub.3]) 0.387 0.392
f (C-H/CH) (b)
f (Se-CN/CN)
Deformations
f (F-C-F) (b) 1.305 1.291
f (F-C-Se) (b) 0.931 0.936
f (C-Se-C)
f (Se-C[equivalent to]N)
f (H-C-H) (b)
f (H-C-Se) (b)
Reference (1)
Force constant (a) C[F.sub.3]SeCl C[F.sub.3]SeBr
Bond stretchings
f (C-F) (b) 6.033 5.976
f (Se-C[F.sub.3]) 2.529 2.69
f (Se-CN)
f (C[equivalent to]N)
f (Se-C[H.sub.3])
f (C-H) (b)
f (C-F/C-F) (b) 0.824 0.818
f (C-F/Se-C[F.sub.3]) 0.364 0.372
f (C-H/CH) (b)
f (Se-CN/CN)
Deformations
f (F-C-F) (b) 1.295 1.252
f (F-C-Se) (b) 0.845 0.868
f (C-Se-C)
f (Se-C[equivalent to]N)
f (H-C-H) (b)
f (H-C-Se) (b)
(a) Units are mdyn [[Angstrom].sup.-1] (1 dyn = 10 [micro]N) for
stretchings and stretch-stretch interactions and mdyn [Angstrom]
[rad.sup.-2] (1 dyn = 10 [micro]N) (1 rad = 10 mGy) for angular
deformations.
(b) Mean values.
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