Electron resonance of SO ( 3 Ʃ ) in the gas phase

Abstract

The electron resonance spectrum of SO has been previously shown to arise from SO in two electronic states, the ground 3 Ʃ - and the excited 1 ∆ state. In this paper the portion of the spectrum assigned to the 3 Ʃ - state is analysed and shown to arise from three isotopic species, 32 S 16 O, 33 S 16 O, and 34 S 16 O. The analysis shows that besides the dominant interaction of the unpaired electronic spins with the magnetic field; other interactions must be taken into account to interpret the spectrum accurately. Interactions with electronic orbital angular momentum of π states mixed in by spin-orbit coupling and with rotationally induced magnetic moments have been observed. Values for parameters measuring such interactions have been determined from the spectrum, and these values lead to a resolution of the first- and second-order contributions to the zero-field molecular constants as well as an approximate value for the spin-orbit coupling constant. The hyperftne structure resulting from 33 S in 33 S 16 O has also been observed and is related to the usual hyperfine coupling constants. The expected line strengths and widths for SO have been calculated and these are compared with the observed quantities. Besides the expected lines from the isotopic SO species in the 3 Ʃ - state, several other lines have been detected. These lines are interpreted as arising from 32 S 16 O in the ground electronic state, but in the first excited vibrational level. The spectrum of vibrationally excited SO allows a value of the spin-spin coupling constant in the first excited vibrational state to be determined.