Internal rotation in propyl mercaptan by microwave spectroscopy

Abstract

The microwave spectra of propyl mercaptan and its six deuterated species were assigned for two rotational isomers, the trans-gauche and trans-trans forms, where the first refers to the isomerism around the central CC bond, and the second, to the one around CS bond. The double minimum splittings of the gauche isomers were directly observed for the species having the symmetry plane in the frame. The rotational constants and the torsional splitting of the gauche isomers of the normal species were determined to be A = 23 907.47 ± 0.09, B = 2345.597 ± 0.006, C = 2250.338 ± 0.009, and Δ ν = 1613.01 ± 0.04 MHz. From the torsional splittings of the normal and SD species and the energy difference of two isomers, the Fourier coefficients of the thiol internal rotation potential function were determined to be V 2 = −353 ± 6, and V 3 = 1310 ± 9 cal/mol on the assumption that V 1 was the same as that of ethyl mercaptan. The dipole moments and their components were also obtained from the Stark effect measurements of the two isomers of the normal and SD species. The directions of the dipole moments were discussed.