Laser-induced fluorescence spectroscopy of the Ga–N2 cluster

Abstract

The first spectroscopic observation of the Ga–N₂ van der Waals cluster is reported. This was formed by laser ablation of a GaAs or GaP target followed by pulsed supersonic expansion in pure nitrogen. Laser-induced fluorescence spectra have revealed two strong band systems above 30000 cm^-1. The first, which has an onset at 33468 cm^-1, is composed of eight observable members of a progression in the van der Waals stretching vibration. This has been assigned to the ²Δ–²Π_3/2 transition correlating with the Ga 442Dâ†�442P_3/2 transition. A Birge–Sponer extrapolation gives a lower limit of 1270 cm^-1 for the van der Waals binding energy in the excited state. At higher wavenumbers another prominent vibrational progression is observed which is attributed to a spin-forbidden transition correlating with the 444Pâ†�442P atomic asymptote, the cluster excited state most likely having ⁴Σ^- symmetry. The excited state undergoes relatively slow spin–orbit-induced predissociation onto the repulsive ²Σ⁺ potential surface followed by rapid emission from the Ga 452S dissociation product.