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 λ = 237 nm. OCS molecules (X¹Σ⁺) were primarily excited to the 1¹A′′ and the 2¹A′ Renner–Teller components of the ¹Σ⁻ and ¹Δ 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 ∼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(X¹Σ⁺, J ≫ 0) fragments, which has a timescale of ∼140 fs. Instead, we suggest to assign the observed oscillations to the excitation of vibrational wavepackets in the 2³A′′ or 2¹A′′ states of the molecule that predissociate to form S(³P_J) photoproducts.