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Photodissociation of gaseous CH3COSH at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Observation of three dissociation channels
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Image of FIG. 1.
FIG. 1.

The 5 μs-resolved CO emission spectra with spectral resolution of 0.25 cm−1 acquired in the range of 1900–2200 cm−1 after photolysis in the presence of Ar at 3000 mTorr.

Image of FIG. 2.
FIG. 2.

Boltzmann plot of ln[N v, J /(2J + 1)] versus E v, J for CO in the v = 1, 2, and 3 levels at zero delay time in the presence of Ar, yielding the corresponding rotational temperature of 1429 ± 42, 1290 ± 53, and 1126 ± 71 K, respectively. N v, J is the relative population of CO in the (v, J) level and E v, J is the corresponding rotational energy.

Image of FIG. 3.
FIG. 3.

Time evolution of CO vibrational population in the v = 1, 2, and 3 level. The population in each level reaches the maximum at 0 μs delay after signal correction with a scaling factor.

Image of FIG. 4.
FIG. 4.

Population decay of OCS(v3) and CH2CO(v2) in the 1950–2080 and 2100–2200 cm−1 region, respectively, after 10 μs delay. OCS starts from v = 6 at 1957 cm−1, relaxes toward low v, and finally vanishes after 280 μs delay. CH2CO(v2) at 2150 cm−1 having partial overlap with OCS seems to decay downward.

Image of FIG. 5.
FIG. 5.

Identification of CH3SH, CH4, and H2S in the 2400–3300 cm−1 region. The spectral region contains three profiles at about 2590, 2920, and 3000 cm−1. CH3SH(v3) and H2S(v1,v3) contribute to the first region, CH3SH(v2) dominates the second one, while CH4(v3) dominates the third one.

Image of FIG. 6.
FIG. 6.

Time-resolved CO2 spectra within the 2300–2400 cm−1 region with a 12 cm−1 resolution resulting from the reaction of CH2 with O2 at 3000 mTorr.

Image of FIG. 7.
FIG. 7.

(a) Area integrated over a low-resolution spectral band of CO2 as a function of delay time with respect to the laser pulse. (b) A plot of ℓn ([CO2]max–[CO2]) versus delay time, yielding a production rate constant of CO2. [CO2]max denotes the maximum concentration in (a).

Image of FIG. 8.
FIG. 8.

Comparison of CO spectra produced between Ar and O2 addition at the same 3000 mTorr. The O2 addition leads to a slight enhancement of CO especially in the 1800–2050 cm−1 region.

Image of FIG. 9.
FIG. 9.

Comparison of the spectra in the 2500-3300 cm−1 region following photolysis of CH3C(O)SH at 248 nm in the presence of Ar or O2 at the same pressure of 2800 mTorr. H2CO (v1) appears in the 2600–2900 cm−1 region after 5 μs and remains at 10 μs delay caused by the reaction of CH2 with O2.

Image of FIG. 10.
FIG. 10.

Three dissociation pathways of CH3C(O)SH on the ground state surface were computed previously (Ref. 25 ) using hybrid density functional theory B3LYP with cc-pVTZ and other basis sets. Dissociation energy of CH2CO denoted with dashed line is adopted from Ref. 47 .

Image of FIG. 11.
FIG. 11.

Vibrational population of CO product obtained by (a) experimental observation, (b) prior distribution of CH2 + H2S + CO, and (c) prior distribution of CH3SH + CO. Population of CO(v = 1) is normalized for comparison.

Image of FIG. 12.
FIG. 12.

The Ar pressure dependence of the CO area intensity over the low resolution spectra obtained at 0 μs delay. According to Eq. (9) in the text, the experimental data are fitted to yield the optimized rate constants in units of cm3 molecule−1 s−1 for the collision-induced internal conversion.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Photodissociation of gaseous CH3COSH at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Observation of three dissociation channels