Ground state spectroscopic constants of isothiocyanic acid, HNCS, from its microwave and millimeter wave spectra combined with far infrared data

Abstract

Abstract The microwave and millimeter wave spectra of isothiocyanic acid, HNCS, in the ground vibrational state have been investigated in the frequency region 8–300 GHz. The a-type R-branch transitions have been assigned up to J = 25 and Ka = 4, and the a-type qQ1 branch transitions up to J = 45. No b-type transitions could be identified in the frequency region covered. The far infrared data reported by Krakow, Lord, and Neely [J. Mol. Spectrosc., 27, 148 (1968)] were combined with our millimeter wave data in order to determine reliable spectroscopic constants. The rotational Hamiltonian, Watson's formalism with S reduction, has been extended empirically to higher order to facilitate the fitting of the large centrifugal distortion effects. The obtained constants are: A = 1357.3 GHz; B = 5883.4627 MHz; C = 5845.6113 MHz; D J = 1.19393 kHz; D JK = −1025.37 kHz; D K = 51.57 GHz; d 1 = −13.781 Hz; d 2 = −4.59 Hz. The 14N quadrupole coupling constant has also been determined: χaa = 1.114 MHz.