Infrared diode laser and millimeter-wave spectroscopy of the NCl radical: Vibrational and isotopic dependences of molecular constants

Abstract

The infrared diode laser and millimeter-wave spectra of the nitrogen chloride radical in the X 3Σ − state have been observed in a DC glow discharge plasma of a N 2 and Cl 2 mixture, yielding spectroscopic information on 14N 35Cl up to v = 4 and 14N 37Cl up to v = 3. The observed infrared and millimeter-wave spectra have been simultaneously included in a least-squares analysis to determine Dunham coefficients for the vibrational and rotational energies and similar terms for the fine structure interactions. The analysis has shown that isotopic relations based on the Born-Oppenheimer approximation do not hold for the vibrational frequency, the rotational constant, and the spin-spin and spin-rotation interaction constants. It has been found that the first derivative of the spin-spin interaction constant with respect to the internuclear distance is correlated with the change in the equilibrium internuclear distance caused by the b 1Σ + ← X 3Σ − excitation.