Knowledge Bank

A study of the microwave spectrum of isopropyl mercaptan in the region 8--26.5 GHz has demonstrated the existence of both trans and gauche isomers. Transitions due to the gauche species are split into doublets by the internal rotation of the SH-group. The energy difference between the two isomers is of the order of 150 cal/mole with the trans isomer the more stable. Measurements have been extended to the deuterated species, ($CH3)2CHSD$, and transitions have been assigned to both the trans and gauche isomers. A set of lines for each isomer of both the H -- and the D -- species has been assigned to an excited vibrational state. The rotational constants of the trans isomer are A = 7892.90 MHz, B = 4414.39 MHz, C = 3158.06 MHz for the H-species and A = 7680.70 MHz, B = 4300.03 MHz, C = 3132.67 MHz for the D-species. Stark effect measurements on the trans isomer show that $\mu a=1.59$ D and $\mu e=0.24$ D are the dipole moment components.