ArI 2 (X)→Ar+I 2 (B) photodissociation: Comparison between linear and T-shaped isomers dynamics

Abstract

Quantum dynamical calculations on ArI 2 photodissociation have been performed using ab initio and semi-empirical potential energy surfaces, which support both linear and T-shaped isomers in the ground electronic state. Whereas the photon absorption spectra for the T-shaped isomer consist of narrow and intense bands, those for the linear isomer result from the superposition of a continuous background and peaks due to linear quasi-bound states. Vibrational distributions for the linear isomer are broader than those originating from the T-shaped one. Rotational distributions for the linear isomer are smooth and characteristic of a fast dissociation dynamics, whereas those for the T-shaped isomer are highly oscillatory. Implications of these results on the interpretation of experimental data are discussed.

Ar ··· I 2 : A model system for complex dynamics

“…This can be understood as an indirect indication of the IVR mediated fragmentation mechanism. These features were qualitatively reproduced by recent quantum calculations (Roncero et al, 2001b) performed with only the B electronic state, thus neglecting the EP dissociation channel.…”

“…The contour plots of the calculated vibrational wave functions for zero total angular momentum (Roncero et al, 2001b) are presented in Fig. 8 for the lowest Van der Waals levels of the X state (r fixed at its equilibrium value), and of the (B, v = 21) states (Buchachenko et al, 2000b;Roncero et al, 2001b). The ground n X = 0 Van der Waals level of the X state has a dissociation energy of 208.9 cm −1 and corresponds to the Tshaped isomer, as well as the next four levels.…”

“…Fig. 9 shows the B ← (X, v = 0) absorption spectra for the 0 ++ ← 1 −− rotational transition obtained with the DIM PT1 X and B PES for the T-shaped and linear isomers (upper and lower panels, respectively) (Roncero et al, 2001b). The spectrum of the T-shaped isomer exhibits a sequence of bands assigned to definite vibrational states v of I 2 (B).…”

“…Note the difference in scale for the absorption cross sections from the T-shaped and linear isomers. (Reprinted from (Roncero et al, 2001b) Levy (1981) has been multiplied by a factor of 10 to match the other results. Curve labelled relative quantum yield : LIF intensity divided by absorbance from Goldstein et al (1986).…”

“…Ratio of absorption cross sections of the linear and T-shaped isomers for the DIM PT1 PES. (Reprinted from ref (Roncero et al, 2001b)…”