Chemical quenching of excited-state gallium (2S) atoms by methane in argon matrices

The ground- and excited-state reactions of matrix-isolated Ga atoms with methane have been investigated by UV-visible and infrared spectroscopies. Gallium atoms were co-condensed with methane-doped Ar (1:10 CH sub 4 /Ar) at 12K. No evidence was found for a ground-state reaction. Gallium atom photoexcitation at 354 nm ( exp 2 P- > exp 2 S) resulted in rapid disappearance of all Ga UV absorptions, and the appearance of IR absorptions, which are attributed to methylgallium hydride. IR vibrational mode assignments were made with the aid of data from isotopically substituted molecules formed in CD sub 4 - and exp 13 Ch sub 4 -doped Ar matrices. Subsequent visible broad-band photoexcitation ( > 495 nm) of matrices containing CH sub 3 GaH caused complete removal of all IR absorptions due to CH sub 3 GaH and full recovery of UV-visible absorptions due to Ga atoms, indicating that the reaction is fully photoreversible.