Collision-induced absorption of gaseous silane in the far infrared

The collision-induced spectrum of SiH4 has been studied between 32 and 400 cm−1 with a Michelson interferometer. From a band shape analysis and a spectral moment calculation, it is concluded that the octopole moment Ω dominates the induction process, but that current treatments of octopolar induction cannot completely account for the data. Either these treatments are incomplete in some way, or a second induction mechanism makes a significant contribution to the absorption. If the discrepancies are attributed to the hexadecapole moment Φ, then it is found that ‖Ω‖= (2.6±0.3) ×10−34 esu cm3 and ‖Φ‖= (5.9±1.9) ×10−42 esu cm3. An algebraic error in the symmetrized calculation of Ozier and Fox (1970) is corrected and the minor changes in the spectra due to the correction are discussed.