Vacuum ultraviolet photodissociation dynamics of OCS via the F Rydberg state: The S(3PJ = 2, 1, 0) product channels

Abstract

Vacuum ultraviolet (VUV) photodissociation dynamics of carbonyl sulfide was investigated experimentally by using a tunable photolysis light source and the time-sliced velocity map ion imaging technique. Ion images of S(3P J =2, 1, 0) dissociation products were measured at five photolysis wavelengths from 133.26 nm to 139.96 nm, corresponding to the F Rydberg state of OCS. Two dissociation channels: S(3P J)+CO( X1Σ+) and S(3P J)+CO( A3Π) were observed with the former being dominant. The vibrational states of CO co-products were partially resolved in the ion images. The product total kinetic energy releases, anisotropy parameters ( β), and the branching ratios of high-lying CO vibrational states were determined for the S(3P J )+CO( X1Σ+) channel. We found that the anisotropy parameters suddenly changed from negative to positive when OCS was excited to the higher vibrational levels of the F state. Furthermore, the anisotropy parameters for S(3P J) products of J = 2, 1, 0 were even different. These anomalous phenomena may result from the simultaneous existence of both parallel and perpendicular dissociation mechanisms, suggesting the involvement of other electronic states with different symmetry in the initially-excited energy region. This work provides a further understanding of the nonadiabatic couplings in the VUV photodissociation process of OCS.

Unraveling the Rich Fragmentation Dynamics Associated with S–H Bond Fission Following Photoexcitation of H2S at Wavelengths ∼129.1 nm

“…The product total translational energy, P ( E T ), distributions were obtained using tunable VUV pump and probe sources along with HRTOF detection . The experimental apparatus and methods have been detailed previously. ,− The H 2 S sample (typically 30% seeded in Ar) was introduced into the interaction volume in the form of a pulsed jet. The photolysis photons at λ ∼ 129.1 nm were generated by difference four-wave mixing (DFWM) involving two λ = 212.556 nm photons, and one λ ∼ 600 nm photon overlapped in a stainless-steel cell filled with a 3:1 ratio Ar/Kr gas mixture.…”

Exploring the vacuum ultraviolet photochemistry of astrochemically important triatomic molecules

“…The photodissociation of OCS at near UV wavelengths λ >200 nm is dominated by the spin-allowed channel yielding S( 1 D) + CO(X) products; the latter are formed vibrationally ‘cold’ but rotationally ‘hot’, in at least qualitative accord with that expected given the forces introduced by a bent ← linear excitation process [ 84 ]. The same product channel has been investigated using TSVMI methods following excitation in the range 142.98 ≤ λ ≤ 154.37 nm [ 75 ] and other single-bond fission channels yielding S( 1 S) + CO(X) [ 85 ] and S( 3 P) + CO(A) [ 86 ] products have also been reported when exciting at similar VUV wavelengths.…”