Analysis of the n7Cn9 and 2n7Kn9 band complexes of dicyanoacetylene (NC–CC–CN)

The very weak n7Cn9 band complex near 368 cmK1 and the 2n07 Kn9 system near 404 cmK1 in the infrared gas spectrum of dicyanoacetylene (NC–CC–CN) have been analysed. In the n7Cn9 band system, we have assigned 68 subbands, reaching upper vibrational states with n7 up to 3 and n9 up to 8. The 11 subbands of the 2n07 Kn9 system with n9 up to 7 could be observed because of intensity transfer from the n3Kn9 band, a result of the strong anharmonic interaction between the n3 and 2n07 states. The combined data from the previously studied n9 band together with the n7Cn9 and 2n7Kn9 bands were used for a global rovibrational analysis from which a full set of molecular parameters for the n7 and n9 modes has been deduced. A recently developed theory of intensities in such band systems has been applied to the n7Cn9 band. Examples of intensity calculations illustrate some spectacular effects of the rotational and vibrational [-type resonances on intensities. The observed intensities are in good agreement with the predicted values within the expected J-ranges. q 2005 Elsevier B.V. All rights reserved.