The Fulcher Bands of HD andD2

Abstract

First an account is given of the production and photography under high dispersion of the molecular spectra of ${\mathrm{H}}_2$, HD and ${\mathrm{D}}_2$ from the ultraviolet to the infrared. Besides the HD and ${\mathrm{D}}_2$ lines many new ${\mathrm{H}}_2$ lines were found. The Fulcher bands ($1s\sigma ·3p\pi {}_{}{}^3{}_{}{}^{}\Pi \to 1s\sigma ·2s\sigma {}_{}{}^3{}_{}{}^{}\Sigma$ transitions) are given and the constants of these bands compared for the three isotopic molecules. One component of the higher vibrational levels of the initial state is predissociated. From this it follows that the heat of dissociation of the normal molecule must lie between 4.43 and 4.52 volts.