Methane line parameters in the HITRAN2012 database

Abstract

The compilation of methane molecular line parameters was updated to include new global analyses and measurements for 12CH4, 13CH4 and 12CH3D. Over 70% of the methane parameters in HITRAN2008 were replaced; existing parameters retained were the microwave lines and the Dyad of 13CH4 near 7μm and ν6 of 13CH3D near 8.7μm, 12CH3D (7–4076cm−1), hot bands of 12CH4 (1887–3370cm−1) and normal sample CH4 (4800–5550cm−1 and 8000–9200cm−1). With a minimum intensity at 296K in units of cm−1/(moleculecm−2) set to 10–37 for the far-IR and 10–29 for the mid- and near-IR, the methane database increased from 290,091 lines in HITRAN2008 to 468,013 lines, and three-fourths of these involved the main isotopologue. For 12CH4 and 13CH4, bands from the ground state were revised up to 4800cm−1. For the first time, 13CH4 and 12CH3D line parameters near 2.3μm were included. Above 5550cm−1, the new compilation was based on empirical measurements. Prior laboratory results were replaced with extensive new measurements using FTIR (5550–5852cm−1), differential absorption spectroscopy (DAS) and Cavity Ring Down Spectroscopy (CRDS) (5852–7912cm−1). Ground state J values for nearly half of the measured lines in this range were obtained, either by confirming quantum assignments of analyses or by using spectra at 80 and 296K. Finally, over 11,000 measured positions, intensities and empirical lower state energies (obtained using cold CH4) were also added for the first time between 10,923 and 11,502cm−1. Available pressure broadening measurements from HITRAN2008 were transferred into the new compilation, but 99% of the lines were given crudely-estimated coefficients. New measured intensities and broadening coefficients were included for far-IR transitions, and high accuracy line positions were inserted for the stronger P, Q and R branch transitions of ν3 at 3.3μm and 2ν3 at 1.66µm.