Time-dependent photodissociation of methyl iodide with five active modes

Abstract

Advances in the time propagation of multidimensional wave packets are exploited to present the A-band photodissociation dynamics of methyl iodide for five active vibrational modes on the three relevant excited ab initiu potential surfaces. The five modes considered represent all of the experimentally observed dynamical activity. The only modes neglected are the asymmetric C-H stretch and the asymmetric deformation of the methyl group. The kinetic energy operator corresponding to these five degrees of freedom is derived. The fully quantum mechanical calculation was implemented upon grids using 2880 distinct time-dependent configurations, determined by the multiconfigurational time-dependent Hartree algorithm, for each electronic state. All of the currently known experimental results regarding the umbrella vibration, symmetric C-H stretching vibration, perpendicular rotation, and parallel rotation of the photodissociated methyl radical fragment are well reproduced. The full wavelength dependence of all of these quantities is determined. The wavelength dependence of the energy deposited into translational, vibrational, and rotational motion is also given. The time evolution of the modes is presented in the context of correlated motion and its effect upon the dissociative process. Many of the details of the dynamics inherent to the conically intersecting nature of the excited surfaces is delineated. In particular it is shown that the Jahn-Teller distortion of the * Q i state is irrelevant in contributing to the perpendicular character of resonance Raman depolarization ratios. Results are compared and contrasted to previous calculations employing the collinear pseudotriatomic model with optimized empirical surfaces or the bent pseudotriatomic model with the same ab initio surfaces.

Photodissociation dynamics of the methyl radical at 212.5 nm: Effect of parent internal excitation

“…This actually allows us to study the photodissociation dynamics of both cold and hot methyl radicals simply by choosing different radical products with time delays. CH 3 I photodissociation has been studied extensively and most of the present knowledge on the CH 3 I photodissociation dynamics involving the A band have been provided in several recent theoretical studies [13][14][15] and a recent review article by Kinsey et al 16 Recently, the nascent quantum state product distributions corresponding to both I( 2 P 3/2 ) and I( 2 P 1/2 ) have been fully determined by Eppink and Parker using the velocity map imaging technique. 17 There are two groups of CH 3 radicals ͑fast and slow͒ corresponding to the two I atom product states.…”

Dynamics of radiationless transitions in large molecular systems: A Franck–Condon-based method accounting for displacements and rotations of all the normal coordinates

“…15,16 Several general methods have been described in the literature for full quantum dynamical calculations, [17][18][19] they have been applied to non-radiative electronic transitions with very promising results, 19,20 but their applications to large molecular systems remain limited to a few cases. [21][22][23] In this paper we intend to give a contribution in this direction by developing a simple and reliable approach tailored for the study of electronic transitions, in which all vibrational degrees of freedom are taken into account in the calculation of the quantum evolution operator. The inclusion in the dynamics of the whole set of vibrational coordinates as active modes, i.e.…”

The photodissociation of CH3I in the red edge of the A-band: Comparison between slice imaging experiments and multisurface wave packet calculations

“…43 These potential surfaces were used in classical trajectory 42,43 and wave packet calculations. 37,39,44 Improved potential energy surfaces were produced by Xie et al 45 based on contracted SO configuration interaction calculations using a better basis set and more spin-free configurations, in order to better reproduce the absorption spectrum of CH 3 I. These improved potential surfaces were used in reduced dimensionality wave packet calculations of rotationally selected CH 3 I and CD 3 I ͑Ref.…”