High-resolution infrared identification of HOCS⁺ with difference frequency laser spectroscopy

Abstract

The v ₁ fundamental band of HOCS⁺ has been observed in absorption in a hollow cathode discharge with a difference frequency laser system. The precise spectroscopic parameters have been determined through a least squares fit of more than 550 lines to an effective vibration-rotation hamiltonian. It has been concluded that the species is HOCS⁺, since the vibrational frequency (v ₀ = 3435·1636 cm^-1) is very likely to be the O-H stretch, and not an S-H or C-H stretch. Rotational transition frequencies for K_a ⩽ 2 are calculated to assist the search for the species in interstellar space and in the laboratory. An isomer, HSCO⁺, has been searched for in the range of 2450–2600 cm^-1 (expected S-H stretch frequency region) without success.