Analysis of the v7+v9 and 2v7-v9 band complexes of dicyanoacetylene (NC-CC-CN)

The very weak v(7) + v(9) band complex near 368 cm(-1) and the 2v(7)(0) - v(9) system near 404 cm(-1) in the infrared gas spectrum of dicyanoacetylene (NC-CC-CN) have been analysed. In the v(7) + v(9) band system, we have assigned 68 subbands, reaching upper vibrational states with v(7) up to 3 and v(9) up to 8. The 11 subbands of the 2v(7)(0) - v(9) system with v(9) up to 7 could be observed because of intensity transfer from the v(3) - v(9) band, a result of the strong anharmonic interaction between the v(3) and 2v(7)(0) states. The combined data from the previously studied v(9) band together with the v(7) + v(9) and 2v(7) - v(9) bands were used for a global rovibrational analysis from which a full set of molecular parameters for the v(7) and v(9) modes has been deduced. A recently developed theory of intensities in such band systems has been applied to the v(7) + v(9) band. Examples of intensity calculations illustrate some spectacular effects of the rotational and vibrational l-type resonances on intensities. The observed intensities are in good agreement with the predicted values within the expected J-ranges. (C) 2005 Elsevier B.V. All rights reserved.