Time-resolving the UV-initiated photodissociation dynamics of OCS

Abstract

We present a time-resolved study of the photodissociation dynamics of OCS after UV-photoexcitation at $\lambda =237$ nm. OCS molecules ($X{}^1{\Sigma }^{+}$) were primarily excited to the $1{}^1{A}^{\prime \prime }$ and the $2{}^1{A}^{\prime }$ Renner-Teller components of the ${}^1{\Sigma }^{-}$ and ${}^1\Delta$ states. Dissociation into CO and S fragments was observed through time-delayed strong-field ionisation and imaging of the kinetic energy of the resulting CO${}^{+}$ and S${}^{+}$ fragments by intense $790$ nm laser pulses. Surprisingly, fast oscillations with a period of $\sim 100$ fs were observed in the S${}^{+}$ channel of the UV dissociation. Based on wavepacket-dynamics simulations coupled with a simple electrostatic-interaction model, these oscillations do not correspond to the known highly-excited rotational motion of the leaving CO$(X{}^1{\Sigma }^{+},J\gg 0)$ fragments, which has a timescale of $\sim 140$ fs. Instead, we suggest to assign the observed oscillations to the excitation of vibrational wavepackets in the $2{}^3{A}^{\prime \prime }$ or $2{}^1{A}^{\prime \prime }$ states of the molecule that predissociate to form S${(}^3{P}_J)$ photoproducts.

arXiv comment25 pages, 5 figures

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• A Laboratory Frame Density Matrix for Ultrafast Quantum Molecular Dynamics