A detailed analysis of the nu(2)/nu(5)/nu(3)+nu(6) band system of (CH3I)-C-13 and (CH3I)-C-12

The infrared spectra of (CH3I)-C-13 and (CH3I)-C-12 in the region of the bands nu(2), nu(5), and nu(3) + nu(6), 1200-1600 cm(-1), have been studied at an effective resolution better than 0.0025 cm(-1). The excited states of these bands form a complicated level system with a number of resonances coupling the levels. Accordingly, the bands have been analyzed by diagonalizing the complete energy matrices with all the interactions simultaneously taken into account. The computational procedure is discussed in detail. In the case of (CH3I)-C-13, 6302 observations including 145 perturbation-allowed transitions have been least-squares fitted by using a model with 44 free parameters. The standard deviation of the fit was 0.00014 cm(-1). For (CH3I)-C-12, 7161 transitions including 351 forbidden lines have been fitted using practically the same model as above. The standard deviation in this case was 0.00015 cm(-1). (C) 1996 Academic Press, Inc.