Simultaneous analysis of the ν₂and ν₄bands of methane

Vibration-rotation spectra of the ν2 and ν4 bands of CH4 have been analysed by a simultaneous diagonalization of the hamiltonian matrices for the v 2=1 and v 4=1 states coupled by the Bξ2,4 Coriolis interaction term. The effective hamiltonians used extend to sextic centrifugal distortion terms. The results are a significant improvement on any previous analysis; 438 assigned transitions up to J′=16 have been fitted with an overall standard deviation of 0·016 cm-1. The method used is compared with an alternative theoretical approach given by Berger.