Infrared spectrum of 13CH3I in the 2770-3200cm-1 region:: Rotational analysis of the fundamentals ν1 and ν4 together with 2ν5 and ν3+ν5+ν6

The high resolution infrared spectrum of (CH3I)-C-13 in the region of the fundamental bands nu(1)(A(1)) and nu(4)(+/-1)(E) near 3000 cm(-1) have been studied in detail with an effective resolution better than 0.0040 cm(-1). In addition to these fundamentals, an overtone band 2 nu(5)(0) and a PAPE band nu(3) + nu(5)(-/+1) + nu(6)(+/-1) have been identified in the region. The excited states of these four bands, together with 2 nu(2) + nu(3), nu(2) + 2 nu(6)(-/+2), nu(2) + nu(5)(+/-1), nu(2) + nu(3) + nu(6)(+/-), 2 nu(5)(-/+2), nu(3) + nu(5)(-/+1) + nu(6)(-/+1), 2 nu(3) + 2 nu(6)(0,-/+2) and 3 nu(3) + nu(5)(+/-1), 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. Special care has been paid to eliminate the effects of the near-lying vibrational levels on the constants of the fundamentals. Especially the influence of the strong Fermi resonance nu(1)/2 nu(5)(0) has been studied. The model with 60 free parameters could reproduce the 4610 experimental transitions with only fairly modest standard deviation of 4.3 X 10(-3) cm(-1). The physically reasonable values for the parameters were considered more important than just the final standard deviation of the least squares fit. (C) 1998 Academic Press.