FTIR and dispersive gas phase absolute infrared intensities of hydrocarbon fundamental bands.

New experimental intensity results obtained by band integration from the PNNL (Pacific Northwest National Laboratory) spectral library are reported for 26 CH vibrations of methane, acetylene, ethylene, ethane, allene, propyne and cyclopropane. The PNNL intensity values range from 3.1 to 185.4 km mol-1 and are in excellent agreement, rms difference of 3.1 km mol-1, with earlier low resolution intensity results. QCISD/6-311++G(3d,3p) and QCISD/cc-pVTZ theoretical results are in good agreement with the PNNL intensity values with rms differences of 4.4 and 4.9 km mol-1, respectively. Charge-charge transfer-dipolar polarization model parameters at both quantum levels indicate that the charge transfer-dipolar polarization contributions to the intensities are much larger than those owing to the movements of static equilibrium charges on hydrogen for these vibrations except for the CH vibrations of acetylene that is known to contain very acidic hydrogen atoms. The main effect of the static charge movement comes from its interaction with charge transfer-dipolar polarization owing to the relatively large parameter values of this dynamic electronic contribution. The sum of the charge transfer-dipolar polarization parameters with their interaction with the charge accurately describes the variations in the intensity values of these hydrocarbon vibrations.