The Spectrum of Potassium Hydride

Abstract

The ${}_{}{}^1{}_{}{}^{}\Sigma \to {}_{}{}^1{}_{}{}^{}\Sigma$ molecular spectrum extending from 4100A to 6600A has been photographed with prism spectrographs with a d.c. potassium arc in hydrogen as source. In absorption spectrographs, also attempted, the bands were masked by alkali bands except in a short region, 4600A to 4800A. The spectrum is of the many-lined type. Analysis disclosed 29 bands falling into five $v^{\prime }$ progressions. Each band consists of $P$ and $R$ branches only. The rotational and vibrational constants (Table III), which fall into line with the corresponding values for LiH and NaH, are surprisingly different in the two states. ${B_v}^{\prime }$ and ${{\omega }_v}^{\prime }$ show an anomaly, rising with increasing $v^{\prime }$ for low values of $v^{\prime }$, then decreasing. Extrapolation of the vibrational levels indicates that the products of dissociation in the two states differ by the energy of the resonance lines of K(1.60 volts). Heats of dissociation of 1.25 and 2.06 volts are obtained for the excited and ground states, respectively. From potential energy curves a Franck-Condon diagram of intensity is drawn and is in good agreement with observed intensities.