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Synchrotron radiation has research potential in all chemical areas.

The physical and theoretical chemistry program at the 74th CCC provided delegates with a look at the future

The program of the Physical and Theoretical Division at the 74th Canadian Chemical Conference consisted of 180 presentations (130 oral, 50 poster) organized into five specialist symposia and two joint symposia.

Continuing a tradition established in 1989, the division organized a competition for the best contributions made by student presenters in a symposium sponsored by the Division. This was open to any undergraduate or graduate contributor whose presentations had been nominated prior to the conference. The presentations were reviewed by three judges who were very impressed with the quality of all 12 of the contributions.

Two papers were selected for awards: an oral presentation by Eric Johnson, University of Windsor (studying with R. Aroca), entitled, Energy Transfer Between Langmuir-Blodgett Monolayers of neat molecular dyes and a poster presentation by James Francis, McMaster University (studying with A.P. Hitchcock), entitled, Carbon and Oxygen K-shell Excitation of Phenol, Hydroquinone and p-Benzoquinone Studied by Gas Phase Electron Energy Loss Spectroscopy. R.J. Boyd, FCIC (Dalhousie), chair of the Physical and Theoretical Division, presented each winner with a cheque for $200. The funds for these awards were provided from a trust established by the Control Data Corporation of Canada and the Division.

Chemical applications

of synchroton radiation

This four-day symposium was intended to familiarize chemists with the unique capabilities that high-intensity, high-brightness continuum synchrotron radiation (SR) light sources provide for advanced research in essentially all areas of chemistry, from structure to dynamics to biological chemistry to chemical imaging. It was assisted by funding from NSERC, Sumitomo Heavy Industries, Maxwell-Brobeck, the Canadian Institute for Synchrotron Radiation (CISR), 3M Canada and the Ontario Centre for Materials Research.

Six of the eight sessions dealt with scientific applications. The last two sessions were part of a workshop, "Towards a Canadian Synchrotron Radiation Source". This dealt with practical aspects such as the characteristics of new sources and opportunities for Canadian scientists to become involved in SR research, either as users of other sources or through the construction of a facility in Canada.

The symposium opened with a session on X-ray absorption spectroscopy. This demonstrated the wide range of chemical problems which are being tackled by X-ray absorption studies. The second session on surface spectroscopic studies was jointly sponsored by the Surface Science Division. It featured invited talks on NEXAFS (J. Stohr, IBM) and fluorescence-yield studies of surface reactions (J.L. Gland, U. Michigan). The theme of surface studies continued in the third session dealing with new developments on X-ray microscopes and applications of SR to microlithography.

The fourth session, joint with the New Materials Symposium, compared synchrotron X-ray diffraction with reactor-based neutron diffraction techniques, which are frequently being combined. D. E. Cox (BNL) gave several examples of powder diffraction using both X-ray and neutron beams. P. Coppens (Buffalo) showed that accurate electron densities can now be derived from precise synchrotron crystallography. L.T. Delbaere (FCIC, Saskatoon) demonstrated nice examples of the revolution that synchrotron radiation is making in macromolecular crystallography. Other presentations discussed X-ray magnetic scattering Of [URu.sub.2 Si.sub.2] (B.D. Gaulin, McMaster) and applications of soft X-ray scattering to the characterization of polymers (J.S. Tse, MCIC, NRC).

The fifth session dealt with applications of SR to kinetics and chemical dynamics. Several presentations dealt with studies of dynamics on the sub-picosecond time scale through photo-ionization spectroscopies. The first applications of core spectroscopy to studies of cluster molecular beams were described as were elegant space- and time-resolved powder diffraction techniques used to study the kinetics of liquid crystal phase transitions.

The sixth session studied the spectroscopy of gases and solids. Most of this work was carried out at the beam lines of the Canadian Synchrotron Radiation Facility in Wisconsin.

The last two sessions formed the workshop, "Towards a Canadian SR Source". opportunities at existing, developing or proposed facilities in the US were described (D. Attwood, ALS; E.D. Poliakoff, LSU; G. Shenoy, APS, D.H. Bilderback, Cornell). Presentations of prototype lattice designs for a Canadian SR source were outlined by C.B. Bigham (AECL) and L. Dallin (SAL). H. Nakabushi (Sumitomo Heavy Industries) and G.H. Dahlbacka (Maxwell) described commercial SR sources which were competitive with current research facilities.

The afternoon also included an hour of open discussion about the plans for the Canadian facility, which is envisaged as a 1.0- to 1.5-GeV general purpose research machine with significant insertion device capability. Useful feedback on the prototype lattices was provided. There is much interest in developing a facility in Canada before the end of the decade. In this context, CISR has submitted a proposal to fund a detailed design study.

Finally, the successful scientific component of the symposium was concluded with an excellent banquet at the McMaster Faculty Club. Herman Winnik (SSRL) provided an entertaining after-dinner presentation on the history and future of synchrotron radiation, a future which is indeed very bright.

Symposium on molecular

and interfacial dynamics

This symposium consisted of four sessions covering a wide range of experimental and theoretical work. it was organized by T.A. Wildman and R.S. Dumont, McMaster University. The first afternoon began with a discussion of the orientation of water on metal surfaces by Peter Norton (Western (Ontario). Norton and co-workers found that water at low coverage on Ni(110) adopts a non-hydrogen bonded structure with the molecular plane parallel to the surface. At higher coverage, hydrogen bonding leads to a bilayer structure similar to hexagonal ice.

Sinjun Dixon-Warren (Toronto) described the process of photo-induced charge transfer dissociation for molecules on metal surfaces. He reported that Cl-ions were detected following irradiation of [CCl.sub.4] on Ag(111) at 193, 222 or 248 nm but not after irradiation at 308 or 350 nm. Thermal desorption and Auger spectroscopic studies indicated that [CCl.sub.4] reacts with Ag(111) at low coverage.

Michael Dignam (Toronto) presented recent results on the theory of Raman scattering by molecules absorbed onto the small particles of a dispersed solid. Of particular interest were scattering by "inactive" vibrational modes and interparticle coupling effects on intensity, E. Johnson (Windsor) then gave his award-winning presentation on the energy transfer between Langmuir-Blodgett monolayers of molecular dyes which occurs by an electric dipole mechanism with delocalization over distances greater than the donor-acceptor layer separation.

V.C. Reinsborough (Mount Allison) described work on the structure and composition of mixed hydrocarbon/fluorocarbon micelles. Using stopped flow techniques, he found that the complexation kinetics of [Ni.sup.++] by PADA are significantly faster in mixed micelles. Glenn Penner (Guelph) described his [H.sup.2] NMR studies of the molecular structure and motions of tris(trimethylsilyl)amine. He concluded that the molecule is trigonal planar about the nitrogen and undergoes as many as four distinct rotational motions within the solid. Finally, David Sliwinski (Brock) described work on the [Si.sup.29] NMR of synthetic forsterite [Mg.sub.2][SiO.sub.4], and willemite [Zn.sub.2][SiO.sub.2] doped with paramagnetic transition metal ions. The authors found stretched exponential spin-lattice relaxation that they ascribed to inefficient spin diffusion from the dilute impurity centres to the dilute [Si.sup.29] nuclei.

Two sessions dealt with dynamics in the gas phase. Tucker Carrington Jr (Montreal) described a new model for rovibrational interactions in polyatomics that includes Coriolis coupling in zeroth order. Mangala Krishnan (Montreal) then described his work with Carrington on the simplification of rovibrational Hamiltonians using a generalized unitary transformation.

Tom Slee (Waterloo) discussed a new and efficient iterative scheme for the calculation of rovibrational states of weakly-bound complexes. Application of the iterative secular equation method, which employs perturbation theory to optimally improve the basis for subsequent iterations, to van der Waals complexes provided remarkable agreement with experiment.

Jim Sloan (Waterloo) described the technique of fast time-resolved Fourier transform spectroscopy and its application to the study of the dynamics of several O([D.sup.1.sub.2]) atom reactions of atmospheric relevance, including hydrogen-containing chloro-fluorocarbons, methane and hydrogen sulphide. Such reactions create vibrationally and rotationally excited OH radicals that thermalize within a few collisions. Evidence indicates that the oxygen atom inserts in the X-H bond and that the OH radical leaves before intramolecular vibrational redistribution can occur.

Erik Kruus (Montreal) reported on work in which the attenuation of an infrared laser beam by rotational energy transfer in crossed molecular beams of CO and He, Ar or [N.sub.2] was demonstrated for the first time. Victoria Barclay (Toronto) discussed the effect of collision energy on cross-sections for the reactions H + DCl [right arrow] HD + Cl and H + DCl [right arrow] HCl + D. David Wardlaw (Queen's) described extentions of chaotic two-dimensional billiard models to reactive scattering. The classical dynamics for various square trough potentials were discussed.

William Hase (Wayne State) presented work on the association reaction H + [CH.sub.3] [right arrow] [CH.sub.4] in which the hydrogen is "solvated" by a cluster of 1-13 argon atoms. The calculations were based on variational transition state theory and classical trajectories. A videotape presentation helped to illustrate various classes of events.

Laser induced fluorescence studies of product energy disposal in the reaction S ([D.sup.1]) + [CS.sub.2] [right arrow] [S.sub.2][X.sub.3] ([X.sup.3][[sigma].sub.g]) + CS ([X.sup.1][sigma].sup.+]) were the subject of Jamie Donaldson (Toronto). From the low internal energy content of the products, Donaldson and co-workers concluded that most of the reaction energy appears in translation. Mary Ann Kmetic (Waterloo) reported on a study of melting transitions in [SF.sup.6] [(Ar).sub.n] clusters (n=5-20) done in collaboration with R.J. LeRoy. A videotape presentation based on some of their extensive molecular dynamics simulations illustrated the structures and dynamics.

Pamela Berg (Waterloo) described quasiclassical trajectory studies on the reaction O([D.sup.1]) + [H.sub.2] [right arrow] OH ([X.sup.2 [pi]; v']) + H ([S.sup.2]). The effects of specific reagent excitation on the dynamics were investigated and a videotape presentation was used to depict various trajectories.

The symposium ended with a session on dynamics in the liquid phase. Scott Silence (MIT) began with a description of time-domain "impulsive" stimulated Brillouin scattering experiments that have been used to study triphenyl-phosphite and other complex materials. Time-resolved observations of vibrational and rotational motions, acoustic waves and time-dependent density changes have allowed the examination of structural relaxation dynamics on femtosecond through microsecond timescales.

Geraldine Kenney-Wallace, MCIC, (McMaster) spoke on femtosecond laser studies of molecular motion in solvating liquids using the optically heterodyned optical Kerr effect. Along with co-workers, Kenney-Wallace used the femtosecond laser pulse to induce transient birefringence in the sample. Only those molecules responding to this first pulse were detected by a subsequent polarized (and time-delayed) probe pulse. Librational, translational and diffusional motions have been observed in all liquids studied and, remarkably, molecular vibrational modes have been observed in some cases. David Coker (Boston) discussed his work on the surface hopping trajectory approach to nonadiabatic dynamics of excess electron relaxation in fluids that exhibit localized equilibrium solvated electron states and to electron ejection and trapping in glassy matrices. A videotape presentation illustrated features associated with the nonadiabatic processes, such as the excess electron's digging of an equilibrium solvent cavity after injection into the unperturbed solvent.

Don Irish (Waterloo) described Raman studies aimed at the characterization of species in the system [LiAsF.sub.6]/methyl acetate, which may have implications for the improvement of performance for lithium batteries. Lastly, Michael Menzinger (Toronto) gave two presentations concerning nonlinear dynamics in reactions. The first dealt with new experimental results on the bifurcation structure of the [ClO.sub.2.sup.-]/[I.sup.-] reaction in a continuously stirred tank reactor. The second concerned the formulation of a nonlinear dynamical model of a sensory neuron that is capable of analog-to-frequency transduction. The resulting model is based on partial differential equations of the reaction-diffusion type and should be widely applicable in the fields of neurophysiology and medicine.

The symposium illustrated the importance of synergy between theory and experiment in this dynamic field of research.

High-resolution electronic

spectroscopy

A special symposium in honor of McMaster University's Professor Gerald Wilfrid King, PhD, DSc, FRSC, FCIC, was organized by T.A. Wildman and H. Howard-Lock. The morning session was chaired by David Moule (Brock), the first of King's graduate students in Canada. Donald Ramsay (HIA, NRC) began with a tribute to King's early work with Sir Christopher Ingold on acetylene. King and Ingold showed that acetylene is trans bent in the first excited singlet state, demonstrating for the first time that a molecule in an electronically excited state might adopt an equilibrium geometry different from the ground state geometry.

Ramsay described a program of beautiful and precise spectroscopic work from his own group on glyoxal, another molecule of particular interest to King. Ramsay and co-workers have obtained rotational constants and structures for cis and trans glyoxal in the ground state and in singlet and triplet excited states.

Hafed Bascal (Brock) reported work on the torsion-wagging spectra of thioacetaldehyde in a supersonic jet and on a comparison of experimental results with molecular orbital calculations at the 6-31G level. Carl Brown (NRC) described spectroscopic investigations of association reactions of ground state nickel atoms in the gas phase.

Gerhard Herzberg (HIA, NRC) gave a presentation on the precise determination of the ionization potentials of [H.sub.2] and [D.sub.2]. The best experimental values are 124,417.501 (17) [cm.sup.1] for [H.sub.2] and 124,745.384 (27) [cm.sup.-1] for [D.sub.2] (corrected for the 40 torr pressure shift of helium buffer gas). The best ab initio molecular orbital calculations are now able to reproduce these values to within the experimental error. Continuing this theme, Boris Stoicheff (Toronto) reported on laser studies in which four-wave sum mixing was used to access the ionization limit for hydrogen isotopomers. By monitoring fluorescence, the dissociation energies of [H.sub.2] and [D.sub.2] were determined to be 36118.6(2) [cm.sup.-1] and 36748.7(2) [cm.sup.-1] respectively, in splendid agreement with the best ab initio results.

Bryan Henry (Guelph) chaired the afternoon session. Stephen Wallace (Toronto) described his work on the spectroscopy and dissociation processes of HCl following (2 + 1) resonance enhanced multiphoton ionization in a pulsed supersonic jet. He and his co-workers have assigned over 50 new bands. The V [[sigma].sup.1.sup.+] ([O.sup.+]) valence state, which corresponds to the outer well of the B [[sigma].sup.1.sup.+] ([O.sup.+]) state double-minimum, was probed in detail. Robert Gordon (Queen's) discussed the [S.sub.1] - [S.sub.0] electronic absorption and supersonic jet fluorescence spectra of 1,4-benzodioxan and their implications for the structure of the excited state.

Robert LeRoy (Waterloo) reported on efforts to obtain accurate and precise descriptions of long-range potentials by direct least-squares fitting of vibrational energies and rotational constants for levels near dissociation. Dieter Klapstein (St. Francis Xavier) described work on the electronic structure and vibrational assignments of cyanoformyl fluoride. Ralph Nicholls (York) spoke about the need to achieve realistic computer syntheses of molecular spectra for a wide variety of applications and about his efforts to meet this need.

John Bertie (Alberta) discussed absolute infrared intensity measurements of methanol and methanol-water mixtures. He and his co-workers obtained real and imaginary parts of the optical constants of the liquids for the first time and used these to derive various quantities including molecular dipole derivatives with respect to vibrational displacements. Henrick Kjaergaard (Guelph) reported results of 6-31G(*) molecular orbital calculations on [H.sub.2][O.sub.2]. While OH-overtone intensities were not particularly sensitive to the dipole moment function, the fundamental's intensity decreased when MP2 or CISD correlation corrections were included.

Stuart Rothstein (Brock) described the accurate determination of derivatives of ground-state energies using quantum Monte Carlo techniques. Harmonic and anharmonic vibrational frequencies for LiH compared well with those from other ab initio methods.

A dinner in Professor King's honor was held at the Faculty Club. Members of the King family, McMaster University President Geraldine Kenney-Wallace, NSERC President Peter Morand and many former students, colleagues and friends attended.

Reactive intermediates:

By experiment and theory

This symposium, which was organized by Nick Westwood, MCIC (Guelph) included 17 invited speakers together with several contributed papers. As intended, these encompassed a wide variety of techniques and media, ranging from high-resolution gas phase spectroscopy, to mass spectroscopy and methods for detecting large organic radicals in solution. Various theoretical chemists participated, providing for an interesting interplay between experiment and theory. Several papers addressed the spectroscopy of small unstable molecules.

Peter Bernath (now moved from Arizona to Waterloo) gave an account of the formation and spectroscopy of alkaline metal monovalent organic complexes, and discussed searches for molecules of astrophysical interest, including carbon chains and clusters. A detailed investigation of the electronic spectroscopy of selenoformaldehyde, of relevance to the symposium honoring Gerry King, was given by one of Gerry's former students, Richard Judge (Wisconsin-Parkside).

Dennis Clouthier (Kentucky) discussed investigations of rotationally cold transients prepared using the technique of pyrolysis jet ("fry and freeze") spectroscopy. The second half of his talk concerned work coupling the jet technique with subdoppler intracavity dye laser spectroscopy. Nick westwood's talk was also in two parts, dealing first with studies by Hel PES, FTIR and ab initio calculations of linear/non-linear boron isocyanate molecules, and secondly, with rotationally resolved REMPI-PES of 3p Rydberg states of the NH radical.

Bob McKellar, one of several invited speakers from NRC, presented a plethora of results on long pathlength FTIR studies of gas phase complexes at low temperature (ca. 15K) in which weakly bound species such as ([H.sub.2])2 and its isotopes, [H.sub.2]-rare gas, etc. can only support a limited number of bound states. Mike Gerry (UBC) gave two separate talks, one involving conventional Stark modulated microwave spectroscopy, together math its newer Fourier transform incarnation with applications to rotational perturbations in [BrNC.sup.79] [O.sup.18], and the investigation of weakly bound complexes such as AROCS. The other talk considered velocity modulated infrared spectroscopy of ions, including [HeD.sup.+], and an electronic transition of [N.sub.2.sup.+]. A talk on the generation, spectroscopy, decomposition routes, and ab initio studies for the short-lived formyl chloride and formyl cyanide molecules was presented by Wyn Lewis-Bevan (S. Illinois).

One of the highlights of the Symposium was the review by Harry Kroto,, FRS, (Sussex) on the discovery of Buckminsterfullerene, [C.sub.60], a third form of carbon, and the isolation from soot of milligram quantities of both [C.sub.60] and [C.sub.70], culminating in the beautiful one and five line NMR spectra, respectively, of these species. These materials currently are under intense study worldwide by synthetic and materials scientists.

Interspersed amongst the experimental papers were several papers by experts in the field of computational chemistry. John Goddard (Guelph) addressed the question of what experimentalists want from theory, particularly with regard to structure, stability and spectroscopy. He illustrated his talk with examples from unstable sulphur containing species, paying particular attention to basis set considerations and the problems of spin contamination.

Joseph Francisco (Wayne State) presented a combined experimental/theoretical study of atmospheric chemistry, specifically [O.sub.3] depletion by Cl containing species. John Tse, MCIC (NRC) considered A1 reactions with unsaturated hydrocarbons, and the stabilities and structures of the possible products. Mark Gordon (North Dakota State) discussed many aspects of computational chemistry, in particular, an investigation of [SiLi.sub.n], compounds in which increasing numbers of Li around Si led to interesting structural possibilities.

Several mass spectroscopists were also present and contributed their views on ions, their lifetimes, and reactions. Terry McMahon (Waterloo) discussed reactions of laser ablated metal ions, especially [Al.sup.+], with a variety of reagents in the source region of a high-pressure mass spectrometer. Information on the binding enthalpy and entropy were obtained from the temporal variation of ion intensities. Diethard Bohme (York) presented his work on the reactions of ground state Si ions with polyaromatic hydrocarbons, and the subsequent reactions of the ion complex with stable small molecules. Compelling evidence for graphitic surface chemistry in the gas phase was presented.

Hans Terlouw (McMaster) addressed the technique of neutralization-reionization mass spectroscopy (NRMS) in which mass selected ions are neutralized, forming novel neutral intermediates which can be demonstrated to exist in the dilute gas phase.

Peter Hackett (NRC) gave an interesting talk on the multiphoton excitation, ionization and decay dynamics of refractory metal clusters; one particular observation was the formation of delayed ionization, coined "time-resolved thermionic emission". The solution phase was considered by Janusz Lusztyk (NRC) who discussed the use of laser flash photolysis and time resolved IR detection for the investigation of organic radicals and their reaction rates.

Atomic and molecular

properties

This symposium was organized by V. Smith, FCIC, to complement the Noranda Award Lecture of A. Thakkar. It consisted of three sessions covering research on the fundamental properties of atoms and molecules as studied by both theory and experiment. invited speakers were Steven Alexander (Florida), David Bishop (Ottawa), Russ Bonham (Indiana), Russ Boyd (Dalhousie), Jiri Cizek (Waterloo), J.P. Colpa (Queen's), C.E. Dykstra (Indiana), Ken Edgecombe (Queen's), Robert Leroy (Waterloo), F.W McCourt (Waterloo), Bill Meath (UWO), Robert Parr (N. Carolina), Vedene Smith (Queen's) and A.C. Tanner (Austin).

The Noranda Award presentation by Ajit Thakkar was directed primarily to chemists beginning their careers. An article based on this presentation will be published separately.
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Author:Hitchcock, Adam P.
Publication:Canadian Chemical News
Date:Apr 1, 1992
Words:3588
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