Absorption spectra of the BeH and BeD molecules have been studied in the vacuum ultraviolet using beryllium metal heated in a King furnace filled with 1 atm of hydrogen or deuterium gas. The B2Π–X2Σ+ band system at 1960 Å has been extended and in the region of 1900 to 1700 Å a number of new band systems have been found and analyzed rotationally: B′2Π–X2Σ+, G2Π–X2Σ+, E2Σ+–X2Σ+, and F2Σ+–X2Σ+. A strong band at 1850 Å has been identified as resulting from a transition to a 3d complex (D state) but could not be analyzed. The B, E, F, and D states are Rydberg states yielding an ionization potential of 66 200 ± 500 cm−1 (8.21 ± 0.05 eV). The B state, which has a double minimum potential energy curve, and the G state form a pair of states which result from an avoided crossing. From the analysis of the B′2Π–X2Σ+ system observed in the BeH spectrum a precise value of the ground state dissociation energy is derived: De(X2Σ+) = 17 426 ± 100 cm−1 (2.16 ± 0.01 eV).A weak absorption present at 1980 Å in the BeD spectrum has been tentatively attributed to another 2Σ+–X2Σ+ transition. All the observed excited states exhibit strong perturbations and a C2Σ+ state, probably repulsive, causes strong predissociation. A valueof De(X1Σ+) = 26 328 ± 500 cm−1 (3.26 ± 0.06 eV) is derived for the dissociation energy of the ground state of BeH+.

Colin, R., & Greef, D. D. (1975). The Absorption Spectrum of the BeH and BeD Molecules in the Vacuum Ultraviolet. Canadian Journal of Physics, 53(19), 2142–2169.