On the role of the imaginary part of the relaxation matrix in vibration-rotation bandshape calculations

To study the role of the off-diagonal imagery part of the relaxation matrix in the bandshape formation, the phase factor exp(-ialpha) has been introduced into empirical ECS expressions for the basic cross-section calculations. Analyzing the high-density 3nu(3) CO2 bandshapes in CO2 - Ar gas mixtures, which are extremely sensitive to details of the line mixing effect, we have found that the off-diagonal imagery part of the matrix causes the sufficient shift of the band. Moreover, it causes decreasing the maximum of the branch R and increasing the maximum of the branch P. These effects correspond to the deviations between the measured and ECS calculated band profiles obtained in Ref. 1. This analysis leads to conclusion that the neglect of the off-diagonal imagery part of the relaxation matrix can provide systematic deviations of calculated spectral bandshape from observed one.