Photoacoustic spectra of the overtones of the C-H stretches of N(CH3)3, P(CH3)3, and As(CH3)3 in the gas phase are reported. The observed spectral features are assigned on the basis of the local-mode model. Two bands are observed for each overtone which are assigned to nonequivalent methyl C-H bonds. The higher energy absorption band in each overtone region (Δν = 5, 6, and 7) is assigned to the out-of-plane methyl C-H bonds while the lower energy absorption band is assigned to the in-plane C-H bond. Deconvolution of the overtone bands for Δν(C-H) = 5, 6, and 7 provides additional information with respect to peak position, profile, and line width of the overtone absorptions. Local-mode harmonic frequencies (ωe) and anharmonicities (ωexe) are obtained from an analysis of the spectra. Data suggest that the major factor contributing to the width of P(CH3)3 and As(CH3)3 overtone absorptions is the rotational envelope of the molecule while line widths obtained for N(CH3)3 indicate there is also a major contribution to the width from homogeneous broadening.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry