Infrared Spectrum of 13CH3I in the 2770-3200 cm-1 Region: Rotational Analysis of the Fundamentals nu1 and nu4 Together with 2nu5 and nu3 + nu5 + nu6.

The high resolution infrared spectrum of 13CH3I in the region of the fundamental bands nu1(A1) and nu±14(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 2nu05 and a PAPE band nu3 + nu-/+15 + nu±16 have been identified in the region. The excited states of these four bands, together with 2nu2 + nu3, nu2 + 2nu-/+26, nu2 + nu±15, nu2 + nu3 + nu±16, 2nu-/+25, nu3 + nu-/+15 + nu-/+16, 2nu3 + 2nu0,-/+26, and 3nu3 + nu±15, 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 nu1/2nu05 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. Copyright 1998 Academic Press.