Nuclear spin statistical weights for the trimers and tetramers of C2H2, C2HD, and CO2

Abstract

Nuclear spin statistical weights have been calculated for the rotational levels of C2H2 trimers and tetramers for various geometries having D3h,C3h,D4h,C4h, and D2d symmetries as well as for the several possible planar trimer and tetramer forms of C2HD to assist in the interpretation of high resolution rotation–vibration spectra of these complexes. Results are also given for the trimers and tetramers of CO2. The weights obtained for the 12C2H2 trimer with C3h symmetry as well as the weights for the trimers of 12C2HD are directly applicable to the trimers of HF and H12CN, respectively. Reference is made to earlier calculations of the nuclear spin statistical weights for monomer molecules, the results of which may sometimes be transferred to van der Waals and hydrogen-bonded complexes. A discussion is presented on the role of the separable degeneracies occuring in the classification of energy levels of molecules belonging to one of the Cnh or other point groups with complex characters.