Velocity modulation laser spectroscopy of negative ions: The infrared spectrum of hydroxide (OH−)

Abstract

We report the measurement and analysis of the fundamental vibration–rotation bands of ¹⁶OH⁻ and ¹⁸OH⁻ near 3550 cm⁻¹ by velocity modulation spectroscopy with a color center laser. These bands were analyzed with a least squares fit yielding vibration–rotation constants through sextic distortion terms. From the band origins of the two isotopes, harmonic frequencies and anharmonicities were calculated and a dissociation energy was estimated assuming a Morse potential. Comparisons with high level ab initio calculations are presented. The OH⁻ concentration is found to be dramatically dependent on the presence of metal sputtered on the discharge cell wall.