ULTRAVIOLET SPECTRA OF LiH AND LiD

Abstract

The absorption spectra of LiH and LiD have been observed in the near ultraviolet with high dispersion and absorbing path lengths up to 16 meters. A new band system has been found in each molecule involving the ground state and a ¹Π excited state. Rotational and vibrational analyses of this system have been carried out and rotational and vibrational constants for the upper state have been determined. The observed breaking off of the rotational structure of the bands of this B¹Π—X¹Σ⁺ system has been interpreted as due to predissociation by rotation. With this assumption very accurate dissociation limits of the B¹Π state have been obtained. From these dissociation limits the dissociation energies of the three known electronic states of LiH and LiD have been calculated. In particular the dissociation energies (D₀) of the ground states of LiH and LiD have been found to be 2.4288 ± 0.0002 ev. and 2.4509 ± 0.0010 ev., respectively.