Analysis of the [formula omitted] dyad of 12CH 4 and 13CH 4

Abstract

The reanalysis of the ν 2 ν 4 dyad of 12CH 4 and the first detailed analysis of the same dyad of 13CH 4 have been carried out using new infrared measurements combined with previously published microwave data. The line positions of the ν 2 ν 4 dyad near 7 μm have been measured with a precision of 0.00006 cm −1 using 0.0055 and 0.011 cm −1 resolution spectra recorded with the Fourier Transform spectrometer at Kitt Peak National Observatory/National Solar Observatory. Using a sixth order reduced Hamiltonian, the ground state and the ν 2 ν 4 upper state parameters have been adjusted simultaneously. Standard deviations of 0.065 10 −3 cm −1 involving data through J = 23 for 12CH 4 and 0.062 10 −3 cm −1 involving data through J = 19 for 13CH 4 have been obtained. Over 7100 infrared transitions of methane (with strengths greater than 10 −6 cm −2 atm −1 at 296 K in natural isotopic abundance) have been calculated. The majority of the predicted line positions have individual standard deviations of 10 −4 cm −1 or better.