Analysis of the v9 band complex of dicyanoacetylene and application of a theory of relative intensities to all subbands

The band complex near 107cm(-1) consisting of the fundamental nu(9) of dicyanoacetylene (NC-CC-CN) and its associated hot bands has been analysed from the high resolution infrared spectrum. It turned out that two sets of bands from levels (nu(9) = 0-8) and (nu(7) =1; nu(9) = 0-5) were observable. Including cases where separate e- and f-transitions have been observed, the total number of identified series exceeds 90. The calculations were made with a global rovibrational analysis program adapted for linear sixatomic molecules. We have developed general procedures for calculation of the relative intensities of all allowed transitions between two vibrational polyads in the electronic ground state of a linear molecule, taking into account the wavefunction mixing due to essential or accidental resonances. This supports the assignment procedure in the present case and allows us to understand the dramatic effects on the intensities of different subbands. A good agreement between calculated and observed intensities is obtained with one single intensity parameter for the whole set of subbands. (C) 2004 Elsevier Inc. All rights reserved.