Evidence of isomeric transient species CH2SH and CH3S produced from photodissociation of methanethiol at 157nm

Full text: Tunable VUV synchrotron radiation has been used to investigate the dissociation dynamics of methanethiol(CH3SH) by the technique of photofragment translational spectroscopy using a molecular beam apparatus. Although it is well established experimentally that, at 275-193 nm region, states of CH3SH, 1, 21A'' are excited and both states decompose to CH3S + H channel which is dominant the product branching. We investigate the photodissociation of CH3SH at 157 nm, the S-H fission is a prominent reaction channel still, in addition, a new atomic hydrogen channel is found from the analysis of translational spectroscopy. By tuning the undulator of synchrotron, we found the fragment translational spectra shown different shapes at gap 27 and 28mm, equivalent to 8.6 and 9.5 eV, respectively, absent of CH3S component from the m/e=47 translational spectra at lower photoionization energy, so that we can extract CH2SH signal from m/e=47 bundle. In addition, from the cracking of photoionization of m/e=47, TOF spectra of CH3 and CH2 products showed that the cracking comb come from CH3S and CH2SH components, respectively. On the other hand, experimental results of m/e=2 from carbon deuterated isotope, CD3SH, shown with momentum-matching to m/e=49, CD2SH fragment, confirms isomeric transient species CH2SH and CH3S both are primary products from the photodissociation of 157 nm