The band system of ethane around 7 micron: Frequency analysis of the ν6 band

Abstract

High quality line parameters of the band systems of ethane are required for accurate characterization of spectral features observed in the atmospheres of Jovian planets and their satellites. To date, experimental characterization of the excited vibrational states lying below 1300cm−1 has been made. This includes the torsional bands around 35µm, ν9 (820cm−1), ν3 (990cm−1), ν12−ν9 (380cm−1) and ν9+ν4−ν4 (830cm−1) bands. These earlier high resolution ro-vibrational analyses were made to experimental accuracy. Here, we report a detailed analysis of the weak ν6 band in the 1340–1410cm−1 region using a spectrum recorded at a resolution of 0.003cm−1 and temperature of 200K. The Hamiltonian model included couplings between ν6 and ν9 (in particular with ν9+2ν4 with which it is resonantly coupled) as well as couplings between ν6 and ν8. An excellent fit to within experimental accuracy was obtained. Taking the results of this 5-state fit, together with earlier results on lower lying vibrations, we now have experimental characterization for torsion–vibration states of ethane lying below 1400cm−1.