Methyl Isocyanide Hot Bands in the Region 1300–1560 cm−1

The hot bands accompanying the fundamentals ν6and ν3of CH3NC in the region 1300–1560 cm−1observed in high-resolution Fourier transform recordings complemented by diode laser spectra have been analyzed. The observed transitions comprise 16 subbands of the pair of perpendicularE–Ebands ν6±+ ν8±− ν8±and ν7∓+ 2ν80− ν8±whose upper states form a Fermi dyad, 18 subbands of theA1,2–Eperpendicular bands ν6∓+ ν8±− ν8±/ν7±+ 2ν8±2− ν8±with upper states forming another Fermi dyad, and 8 subbands of the bi-parallelE–Eband ν3+ ν8±− ν8±. The anharmonic, Coriolis, andl-type interactions which couple these upper states with each other and with the states ν7∓+ 2ν8±2, ν4+ 3ν8±1, and ν4+ 3ν8±3have been included in an 18 × 18 Hamiltonian matrix whose eigenvalues model the upper levels of the observed transitions. The values of 46 upper state spectroscopic constants and interaction constants have been adjusted by least squares to 950 observed lines. The results provide a reliable quantitative picture of the interacting states and yield accurate values for the spectroscopic constants of the various states and for the anharmonic constantsx68,x68(g68), andx38.