The Raman Spectra of Phosphorus Methyl and Arsenic Methyl and the Force Constants of the Methyl Compounds of the Fifth Group Elements

The Raman spectra of P(CH3)3 and As(CH3)3 have been photographed and studied in relation to the spectra of the methyl compounds of nitrogen, antimony and bismuth. The low lying frequencies of all of these molecules can be interpreted in terms of a pyramidal structure with the methyl groups acting as units. The existence of only two low lying lines in the spectra of Sb(CH3)3 and Bi(CH3)3 is attributed to an accidental degeneracy resulting from the relatively large mass of the central atom and a particular value of the apex angle. The frequencies computed from a two-constant valence force potential function are in good agreement with those observed. The force constants obtained are tabulated.