Photodissociation Dynamics of OCS near 150 nm: The S(¹S_J=0) and S(³P_J=2,1,0) Product Channels

Abstract

Vacuum ultraviolet photodissociation dynamics of carbonyl sulfide (OCS) was investigated by using the time-sliced velocity map ion imaging technique. Images of the S­(1S J=0) and S­(3P J=2,1,0) photofragments formed in the OCS photodissociation were acquired at six photolysis wavelengths from 147.24 to 156.48 nm. Vibrational states of the CO coproducts were partially resolved and identified in the images. Two main dissociation product channels, namely, the spin-allowed S­(1S J=0) + CO­(X1Σg +) and spin-forbidden S­(3P J=2,1,0) + CO­(X1Σg +), were observed. At each photolysis wavelength, the total kinetic energy releases, the relative population of different CO vibrational states, and the anisotropic parameters were derived. Variations of the relative population were noticed between different spin–orbit states of the S­(3P J ) channel. It was found that the S­(1S J=0) + CO­(X1Σg +) channel is dominated by the 1Σ+ ← 1Σ+ parallel transition of OCS. Interestingly, two types of anisotropic parameters are found at different photolysis wavelengths for the spin-forbidden S­(3P J=2,1,0) + CO­(X1Σg +) product channel. The anisotropic parameters at 147.24 and 150.70 nm are significantly smaller than at the other four photolysis wavelengths. This phenomenon indicates two different nonadiabatic pathways are responsible for the spin-forbidden channels, which is consistent with the barrier structure in the exit channel of one of the triplet states.

Photodissociation of H2S: A New Pathway for the Production of Vibrationally Excited Molecular Hydrogen in the Interstellar Medium

“…In this study, the VUV-pump and VUV-probe method combined with the time-sliced velocity-map imaging (TS-VMI) technique was adopted. This setup has been successfully applied in photodissociation of H 2 O, − CS 2 , , OCS, , etc. The TS-VMI setup was equipped with two independently tunable VUV laser sources.…”

Vacuum ultraviolet photodissociation of OCS via the 21Σ+ state: the S(1D2) elimination channel

“…Such high vibrational excitations of the CO(X 1 Σ + ) photoproducts have also been found in the channel (1) via the 2 1 Σ + state. As suggested by the previous study, 41 one non-adiabatic pathway from the 2 1 Σ + state to the low-lying 1 3 Σ − with a large barrier is responsible for channel (1). In the case of the channel (2) below 150.70 nm, the part of the high vibrationally excited CO(X 1 Σ + ) photoproducts may be formed by another non-adiabatic pathway involving a non-repulsive state.…”

“…While the large β -values also agree well with a parallel character of the 2 1 Σ + ← X 1 Σ + transition. 41 In Fig. 5 and 6, the observed photodissociation dynamics of the channel (2) at 154.37 and 152.38 nm is very similar to that of the channel (3).…”

“…Very recently, photodissociation dynamics of OCS via the six vibrational resonances (v 0 = 0-5) in the 2 1 S + ' X 1 S + band was systematically investigated by using the timeslice velocity-map ion imaging technique in combination with (2 + 1) REMPI, in which the vibrational state-specific dissociation dynamics of channel (1) and channel (3) were revealed and the possible dissociation mechanisms were also discussed. 41 In contrast to many experimental studies of channel (1) and channel (3), there are no investigations of the photodissociation dynamics of channel (2) except for the measurements of relative quantum yields in this VUV absorption band. 42 Nevertheless, photolysis of OCS releases atomic sulfur in the stratosphere that could react to form sulfate to destroy stratospheric ozone 43 and influence the Earth's radiative balance.…”

“…Very recently, photodissociation dynamics of OCS via the six vibrational resonances ( v ′ = 0–5) in the 2 1 Σ + ← X 1 Σ + band was systematically investigated by using the time-slice velocity-map ion imaging technique in combination with (2 + 1) REMPI, in which the vibrational state-specific dissociation dynamics of channel (1) and channel (3) were revealed and the possible dissociation mechanisms were also discussed. 41…”