Laser-induced fluorescence spectroscopy of the Ga-N[subscript 2] cluster

The first spectroscopic observation of the Ga–N[subscript 2] 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[superscript -1]. The first, which has an onset at 33468 cm[superscript -1], is composed of eight observable members of a progression in the van der Waals stretching vibration. This has been assigned to the 2Δ–[X with combining tilde]2Π[subscript 3/2] transition correlating with the Ga 4s[superscript 2]4D[superscript 1] [superscript 2]D ← 4s[superscript 2]4p[superscript 1] [superscript 2]P[subscript 3/2] transition. A Birge–Sponer extrapolation gives a lower limit of 1270 cm[superscript -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 4s[superscript 1]4p[superscript 2] [superscript 4]P ← 4s[superscript 2]4p[superscript 1] [superscript 2]P atomic asymptote, the cluster excited state most likely having [superscript 4]Σ[superscript -] symmetry. The excited state undergoes relatively slow spin–orbit-induced predissociation onto the repulsive [B with combining tilde][superscript 2]Σ[superscript +] potential surface followed by rapid emission from the Ga 4s[superscript 2]5s[superscript 1] [superscript 2]S dissociation product.