POSTER ABSTRACTS

FOR THE 1995 AUSTRALIAN CONFERENCE ON PHYSICAL CHEMISTRY

1) Electronic and Poster Format
Harold W. Schranz and Michael A. Collins
Intramolecular Vibrational Energy Redistribution and Torsional Isomerization:
A Model Classical and Quantum Study

2) Poster Format
H. W. Schranz, T. D. Sewell and S. Nordholm
Statistical and Dynamical Behaviour in Isomerisation Reactions

3) Poster Format
H. W. Schranz and M. A. Collins
A Theoretical Analysis of IVR Involving the Ring Modes in S0 Benzene

4) Electronic and Poster Format
H. W. Schranz
Electronic Dissemination of MultiMedia Information: Potential Impact of the WWW on Chemistry

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Intramolecular Vibrational Energy Redistribution and Torsional Isomerization: A Model Classical and Quantum Study

Canberra, ACT 0200.

An initial classical study [1] considered the nonlinear resonant interaction resulting from kinematic coupling between the torsion mode and other modes in sequentially bonded ABBA type tetra-atomic molecules. It was found that the nonlinear resonant interactions were most likely to involve the symmetric bending mode.

Fig. 1 Facile IVR out of an excited torsion for a two-mode model of CH3OOCH3 near a 2:1 resonance

Later detailed quantum [2] and classical dynamical [3] studies of the nonlinear resonance between the symmetric bend and torsion modes were facilitated by employing a reduced dimensional model (e.g. see Fig. 1). Furthermore, the observed rate of torsional isomerization is compared to the predictions of Transition State Theory. The importance of statistical or dynamical behaviour is thus related to the observed extent of intramolecular vibrational energy redistribution (IVR).

The presentation will be in paper and in electronic poster format [4] facilitating demonstration of the utility of hypertext linked graphics and animations.

[1] H. W. Schranz and M. A. Collins, J. Chem. Phys. 98 (1993) 1132.

[2] M. A. Collins and H. W. Schranz, J. Chem. Phys. 100 (1994) 2089.

[3] H. W. Schranz and M. A. Collins, J. Chem. Phys. 101 (1994) 307.

[4] H. W. Schranz and M. A. Collins, Intramolecular Vibrational Energy Redistribution and Torsional Isomerization: A Model Classical and Quantum Study, First Electronic Computational Chemistry Conference CD-ROM, ARInternet (in preparation, 1995).

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Harold W. Schranz,^* Tommy D. Sewell^# and Sture Nordholm^#
*Research School of Chemistry, Australian National University,

Canberra, ACT 0200.
^#Department of Physical Chemistry, University of Göteborg,

S-41296, Göteborg, Sweden.

A classic prototype reaction in the study of unimolecular reactions is the isomerisation of methyl isocyanide. Most experimental studies have given rate constants consistent with statistical behaviour though some have given indications of non-statistical and mode specific behaviour. Our theoretical study [1] aims to determine the role of statistical and nonstatistical behaviour in the subsequent reaction dynamics of a locally and microcanonically excited molecule (Fig. 1).

Fig. 1. Trajectory calculations and statistical predictions of the rate of isomerisation of CH3NC

[1] T. D. Sewell, H. W. Schranz and S. Nordholm, in preparation.

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Involving the Ring Modes in S0 Benzene

Harold W. Schranz and Michael A. Collins
Research School of Chemistry, Australian National University,

Canberra, ACT 0200.

A potential energy surface for benzene which incorporates the dominant potential couplings is constructed on the basis of ab initio data. The surface is employed for a full dimensional classical mechanical molecular dynamics study of intramolecular vibrational energy redistribution (IVR). Comparisons are made with recent experimental observations [1] regarding the extent and timescale of IVR involving the ring modes.

Fig. 1. IVR out of [[nu]]6 for an initial [[nu]]6²[[nu]]1⁵ excitation

The linewidths found experimentally were instrument limited at 1 cm^-1 for a range of excited ring modes for excitations of between 1200 and 8200 cm^-1 yielding an upper limit on the IVR rate of 0.094 ps^-1. Preliminary trajectory calculations (Fig. 1) reveal an initially rapid decay followed by slow IVR at longer times.

[1] J. A. Nicholson and W. D. Lawrance, preprint.

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of MultiMedia Information:

Potential Impact of the WWW on Chemistry

Harold W. Schranz
Research School of Chemistry, Australian National University,

Canberra, ACT 0200.

Much useful scientific information (text, graphics, audio, movies, computer programs, experimental data) can be stored on computers networked to the Internet. The problem resides in how to access this information as well as how to make such information accessible to a wider audience.

Fig. 1. A sample WWW client session

The World Wide Web (WWW), a project initiated by CERN, is a client-server network-based document delivery system that links computers worldwide. A single copy of a set of files (text, graphics, animations) can be shared across the Internet to multiple users by setting up a Web-server. In order to access the information one needs a computer which can run a Web-client program (e.g. see Fig. 1).

Some of the current and potential uses of the WWW are considered from the perspective of chemistry, e.g. electronic conferencing [1] and publishing [2].

[1] First Electronic Computational Chemistry Conference CD-ROM, ARInternet (in preparation, 1995).

[2] H. S. Rzepa, B. J. Whitaker, and M. J. Winter, Chemical Applications of the World-Wide-Web,
J. Chem. Soc., Chem. Commun. (1994) 1907.

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