Determination of the harmonic force field directly from Raman intensity data is demonstrated for acetylene. The Raman intensity invariants α′ and γ′ for the totally symmetric bands of the isotopic species C2H2, C2D2 and C2HD, combined with the G matrix elements, provide sufficient data to determine the normal coordinate matrix elements. These may then be combined with the harmonic frequencies to determine the F matrix elements. An ambiguity exists in the force field results due to the occurrence of two equivalent solutions which cannot be resolved from the Raman intensity data; the ambiguity may be resolved by experimental mean square amplitude data and the calculated an initio force field and bond polarizability invariants. Excellent agreement is obtained with the conventionally determined force field. © 1981 Taylor & Francis Ltd.

Peer reviewed