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The use of discrete variable representations is now commonplace in chemical dynamics calculations. In this paper, we employ spectral difference methods to speed up these calculations. We present five new spectral difference weight functions and compare them with those that already exist in the literature for two different bound state problems. We find that one particular weight we propose, based on a Gaussian function, outperforms all other weights. [ABSTRACT FROM AUTHOR]

The potential energy surfaces (PESs) and S1-T1 spin-orbit coupling matrix element (SOCME) surfaces are investigated for the toluene–X weakly bound clusters (X=Ne, Ar, and Kr). Calculations of the vibrational wave functions using a one-dimensional stretch model are presented and used to determine vibrationally averaged values of the SOCMEs. Our ab initio theoretical results compare well with intersystem crossing rates derived from recent experimental fluorescence lifetime data [Doyle et al., J. Chem. Phys. 122, 194315 (2005)]. Vibrational averaging is shown to change the absolute magnitude of the calculated SOCMEs, but the ratio between them remains very similar to that of the single-point values calculated at the minima of the PESs. [ABSTRACT FROM AUTHOR]

New ab initio potential energy surfaces for the 2Π ground electronic state of the Ar–SH complex are presented, calculated at the RCCSD(T)/aug-cc-pV5Z level. Weakly bound rotation-vibration levels are calculated using coupled-channel methods that properly account for the coupling between the two electronic states. The resulting wave functions are analyzed and a new adiabatic approximation including spin-orbit coupling is proposed. The ground-state wave functions are combined with those obtained for the excited 2Σ+ state [D. M. Hirst, R. J. Doyle, and S. R. Mackenzie, Phys. Chem. Chem. Phys. 6, 5463 (2004)] to produce transition dipole moments. Modeling the transition intensities as a combination of these dipole moments and calculated lifetime values [A. B. McCoy, J. Chem. Phys. 109, 170 (1998)] leads to a good representation of the experimental fluorescence excitation spectrum [M.-C. Yang, A. P. Salzberg, B.-C. Chang, C. C. Carter, and T. A. Miller, J. Chem. Phys. 98, 4301 (1993)]. [ABSTRACT FROM AUTHOR]

Toluene-X van der Waals clusters (where X=Ne, Ne2, Ar, Ar2, Kr, Xe) have been investigated by fluorescence excitation spectroscopy in the region of the S1-S0 transition. With the exception of Xe, for each rare-gas studied, we have assigned cluster transitions in the region of all the strong monomer vibrational bands up to 1000 cm-1 above the origin band. We have further investigated the S1 relaxation dynamics for each vibrational level of each complex, via their fluorescence decay profiles. Clustering with neon has little appreciable effect on the vibrationless S1 lifetime. By contrast, the clusters with argon and krypton exhibit markedly shorter fluorescence lifetimes compared with the monomer. The effect is so severe in the case of toluene-Xe clusters that no fluorescence signals were observed. We interpret these results in terms of an external heavy atom effect in which the rate of intersystem crossing in toluene is influenced by the cluster partner. For clusters built upon excited S1 vibrational levels, the situation is potentially complicated by intramolecular vibrational redistribution and vibrational predissociation (VP). The majority of the fluorescence decay profiles were satisfactorily modeled using single exponential decays. The emission following pumping of the 371 level in the toluene-Kr cluster, however, is an exception. We have modeled the decay of this level with a simple kinetic scheme including VP and determined a predissociation rate of (1.04±0.54) × 107 s-1. [ABSTRACT FROM AUTHOR]

We present a combined experimental and computational study of the external heavy atom effect in van der Waals clusters of para-difluorobenzene (pDFB) with rare-gas atoms. Experimentally, clustering with rare-gas atoms is observed to shorten significantly the S1 fluorescence lifetime compared with that of the pDFB monomer, an effect we interpret in terms of an enhancement of the S1-T1 intersystem crossing rate. In order to test the validity of this widely held assumption, we have calculated the S1-T1 spin–orbit coupling matrix elements in the X-pDFB complexes (X=Ne,Ar,Kr) using a multiconfigurational linear response approach. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]