USING PROGRAM ERHAM TO ANALYZE HIGH-RESOLUTION INFRARED SPECTRA OF MOLECULES WITH INTERNAL ROTORS

Abstract

The effective rotational Hamiltonian for molecules with one or two periodic large-amplitude motions 107, 4483 (1997).} implemented in program ERHAM has been adapted to enable prediction and least-squares fits of rotationally resolved lines in vibration-rotation spectra in the infrared region. The modified program is currently applied to assign the band of methyl formate at 925 cm$^{-1}$ that has been measured at ETH in Zurich on the IFS125 Bruker prototype ZP 2001 FTIR spectrometer 8, 1271 (2007)} at a resolution of 0.001 cm$^{-1}$. An external glass cell with an optical path length of 3 m contained the sample, and 150 interferograms were co-added. Right now it looks as if the splitting into $A$ and $E$ components were a little too small to be resolved sufficiently for positive identification.