Translational spectroscopy of H(D) atom fragments arising from the photodissociation of H2S(D2S): a redetermination of D00(S–H)

The technique of H/D atom photofragment translational spectroscopy has been used to further investigate the collision-free photodissociation of H2S and D2S molecules both in the near ultraviolet (at 218.2 and 221.6 nm) and in the vacuum ultraviolet (at 121.6 nm). Measurements of the H/D atom photofragment angular distributions confirms that the near UV dissociation occurs promptly, following a perpendicular photo-excitation. More than 99% of the resulting SH/SD fragments are formed in their ground vibronic level, with a ca. 3 : 2 preference in favour of the lower (2Π3/2) spin–orbit component. Product rotation accounts for ca. 1% of the available energy in the case of H2S photolysis at these near UV wavelengths (ca. 2% in the case of D2S dissociation). The groundstate SH/SD photofragments can also be photolysed at these near UV excitation wavelengths. Simulations of the kinetic energy distribution of the resulting H/D atomic fragments show that the secondary photolysis also involves a perpendicular transition, and that the partner S atoms are formed in all three 3PJ spin–orbit states. The product energy disposal following 121.6 nm photolysis of D2S closely parallels that deduced in an earlier study of H2S photodissociation at this same wavelength (Schnieder et al., J. Chem. Phys., 1990, 92, 7027). The D-atom kinetic energy spectrum shows clear evidence for the formation of rovibrationally excited SD(A 2Σ+) fragments amongst the primary products, and also suggests an important role for the three-body dissociation process leading to D + D + S(1D) atoms.Given D00(HS–H)= 31 480 ± 40 cm–1, the present results provide a refined value for the S–D bond strength in the D2S molecule; D00(DS–D)= 32 030 ± 50 cm–1; for the SH and SD radical bond dissociation energies; D00(S–H)= 29 300 ± 100 cm–1 and D00(S–D)= 29 700 ± 100 cm–1, and an improved expression for the potential-energy function for the A 2Σ+ state of the mercapto radical.