Velocity modulation diode laser spectroscopy of negative ions: The ν1, ν1+ν2−ν2, ν1+ν3−ν3 bands of thiocyanate (NCS−)

149 transitions in the ν1 band (CN stretch) and the corresponding bending and stretching hot bands of thiocyanate (NCS−) have been measured using velocity modulation spectroscopy with a tunable diode laser. The data were fit to an effective rotation–vibration Hamiltonian, yielding spectroscopic parameters for the (000), (100), (010), (110), (001), and (101) vibrational states. The band origin is ν1=2065.9312(13) cm−1 and the equilibrium rotational constant is calculated to be 0.197 438(61) cm−1. NCS− was prepared in a NH3/CS2 discharge, and unlike the recently studied case of NCO−, vibrational excitation in excess of the rotational temperature (650±200 K) was not observed.