The band spectra of diatomic molecules P<sub>2</sub>, AS<sub>2</sub>, Sb<sub>2</sub> and Bi<sub>2</sub> were investigated in the spectral range 2100–10 000 Å with a medium-size spectrograph, using a discharge tube developed for studies of forbidden lines. A study of the excitation conditions of various bands shows, among other things, that the bands previously ascribed to As<sub>2</sub><sup>+</sup> actually are emitted from a low-lying electronic state of the As<sub>2</sub> molecule. Several new band systems were found, for some of which a vibrational analysis wvas carried out. This permits the identification of three new electronic states for the P<sub>2</sub> molecule and two new states for the As<sub>2</sub> molecule. Four of these states are located below the previously known excited states of these molecules and belong to the triplet term system. A comparison with the N<sub>2</sub> spectrum shows that for this group of diatomic molecules the <sup>3</sup>II<i><sub>g</sub></i> state, located above the <sup>3</sup>Σ<sub><i>u</i></sub><sup>+</sup> state for the N<sub>2</sub> molecule, becomes gradually depressed below the <sup>3</sup>Σ<sub><i>u</i></sub><sup>+</sup> state as the atomic number of the element increases.
S. MROZOWSKI and C. SANTARAM, "Electronic Spectra of P2, As2, and Sb2 Molecules," J. Opt. Soc. Am. 57, 522-530 (1967)