Excited state dynamics in SO2. III. An ab initio quantum study of single- and multi-photon ionization

Abstract

We present an ab initio quantum study of the photoelectron spectra of sulfur dioxide, based on wavepacket propagations on manifolds of ionic, and excited/Rydberg states. We obtain excellent agreement for two different cases. First, the one photon ionization case where we can reproduce all details of the experimental spectrum and demonstrate the influence of the conical intersection between two of the ionic states. Then the multiphoton ionization regime, in which the dynamics of the wave packet on the two lowest singlet states is directly mapped in the spectra via a pump-probe scheme, as proposed in the experimental companion paper [I. Wilkinson et al., J. Chem. Phys. 140, 204301 (2014)].

Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy

“…The periodicity of these signals are in good agreement with those expected from the experimental absorption spectrum 30 and the excited singlet state wavepacket propagation calculations of Lévêque et al 28 As the ionisation process responsible for the sharp component of band (1) 43 which reproduce the characteristic features of the oscillatory component of band (1) (band energetics and ∼150 fs oscillatory period) and support the attribution of the oscillatory component to [2 +1 ] MPI via thẽ G Rydberg state. 43 Notably, the FC window for the [2 +1 ] ionisation process appears to be displaced in coordinate space with respect to the FC window for pump photon absorption based on the ∼0.2π oscillatory phase shift extracted from the SO + 2 TRPEPICO spectra.…”

“…Through the variation of pump photon energy, relative pump and probe laser polarisations, and pump laser intensity we have assigned the dominant, resonantly enhanced ionisation pathways occurring with the implemented probe pulses following single-pump-photon excitation to the Clements bands. Our interpretation of the TRPEPICO spectra is consistent with the SO 2 literature, the surface-hopping calculations presented in Paper II 29 and the partial simulations of the parent molecule MPI spectra presented by Lévêque, Taïieb, and Köppel, 43 from here on referred to as Paper III. 43 In combination, these three papers (consecutively published in this issue of The Journal of Chemical Physics) and the previous work of Lévêque et al 28,34 form a concerted experimental and theoretical effort to elucidate the excited state molecular dynamics occurring following single-photon excitation to the Clements bands.…”

“…Our interpretation of the TRPEPICO spectra is consistent with the SO 2 literature, the surface-hopping calculations presented in Paper II 29 and the partial simulations of the parent molecule MPI spectra presented by Lévêque, Taïieb, and Köppel, 43 from here on referred to as Paper III. 43 In combination, these three papers (consecutively published in this issue of The Journal of Chemical Physics) and the previous work of Lévêque et al 28,34 form a concerted experimental and theoretical effort to elucidate the excited state molecular dynamics occurring following single-photon excitation to the Clements bands. Schematic cross-sections of some of the adiabatic surfaces associated with the initial Clements band dynamics are shown in Fig.…”

“…These results are consistent with the singlet state MPI calculations presented in Paper III. 43 Both singlet and triplet neutral electronically excited states are thought to contribute to all of the photoelectron bands observed in the SO + 2 TRPEPICO spectra. Through pump photon energy and relative laser polarisation studies of the low pump beam intensity SO + 2 and fragment SO + TRPEPICO spectra, we have assigned the dominant MPI probe mechanisms and inferred that ISC occurs from the (B) 1 B 1 /(Ã) 1 A 2 LAS on a sub-picosecond, pump photon energy dependent time scale.…”

“…VI. In synopsis, with the recent results of Lévêque et al 28,34 and those presented in Papers II 29 and III, 43 this paper presents a unified time domain description of the relaxation processes occurring in SO 2 following excitation to the Clements bands.…”