Vibrational spectra of trimethyl gallium species in relation to the force field and methyl group internal rotation

Abstract

Infrared and Raman spectra are reported for Ga(CH 3) 3, Ga(CD 3) 3 and Ga(CHD 2) 3 in the gas phase. These were also examined in the i.r. spectrum in the solid phase at 78 K. The new Raman spectra of the CHD 2 species strongly support earlier i.r. evidence for CH force constant variation during free internal rotation of the methyl groups, from the presence of two bands at 2940 (vs) and 2922 cm −1 (w) identified as due to ν av is and ν † is respectively. The observed a′ and e′ frequencies of the d 0 and d 9 species are used to obtain a force field in which three interaction constants are well defined. The best value of the Ga-C stretching force constant is 2.356(28) mdyn Å −1. In the crystal phase at 78 K, the e′ modes due to δ s Me and ν as GaC 3 are split, indicating a site group symmetry lower than C 3. Gallium and carbon isotope frequency shifts are predicted.