New assignments, line intensities, and HITRAN database for CH 3 OH at 10 lm q Li-Hong Xu, a, * R.M. Lees, a Peng Wang, a L.R. Brown, b I. Kleiner, c and J.W.C. Johns d a Department of Physical Sciences, University of New Brunswick, Saint John, NB, Canada E2L 4L5 b Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA c Laboratoire de Physique Mol eculaire et Applications, Universit e Paris Sud, Batiment 350, 91405, Orsay Cedex, France d Steacie Institute for Molecular Sciences, National Research Council of Canada, 100 Sussex Drive, Ottawa, Ont., Canada K1A 0R6 Received 24 February 2004; in revised form 24 May 2004 Available online 3 July 2004 Abstract The Fourier transform spectrum of CH 3 OH in the 10 lm region has been re-examined at higher pressure and path length than heretofore, as part of a program to provide comprehensive CH 3 OH spectral data for astrophysical and atmospheric applications. With the increase in spectral sensitivity, it has been possible to assign new torsionally excited m 12 ¼ 1 and m 12 ¼ 2 subbands plus further high-K, m 12 ¼ 0 subbands of the m 8 CO-stretching band. Upper-state term values have been determined, and have been fitted to J ðJ þ 1Þ power-series expansions in order to obtain the excited m 8 substate origins. A variety of weaker subbands from other modes has also been identified in the 10 lm spectrum including m 12 ¼ 0, m 12 ¼ 1, and m 12 ¼ 0  1 torsional subbands of the m 7 in- plane CH 3 rock, m 12 ¼ 0  1 and m 12 ¼ 0  2 torsional combination subbands of the m 6 OH bend, and m 12 ¼ 0  2 subbands of the m 5 symmetric CH 3 bend. Line intensities have been retrieved line-by-line from the spectra. A large set of ‘‘unperturbed’’ m 8 transitions has been modeled using the same type of multi-parameter effective Hamiltonian employed successfully for the ground state, with inclusion of the intensities of a subset of the stronger m 8 spectral lines in the fitting in order to obtain appropriate transition dipole terms. Together, a 10 lm methanol database in HITRAN format has been generated. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Methanol; Infrared spectra; Internal rotation; Line positions; Line intensities; Torsional modeling 1. Introduction New assignments for CH 3 OH are reported in the 10 lm infrared region, together with intensity measure- ments and exploratory modeling for the strong m 8 CO- stretching band at 1033 cm 1 . The assignments are based on the analysis of high-resolution Fourier trans- form infrared (FTIR) spectra recorded at greater optical densities in order to identify weaker transitions. The investigation is part of a program to compile a com- prehensive database of line positions and intensities for methanol infrared absorption bands, in response to advances in high-resolution infrared spectroscopy of astronomical sources [1,2] as well as observations in the terrrestrial atmosphere [3]. These applications require reliable simulation of the absorption band profiles at any prescribed conditions of temperature and density. Achieving reliable calculations in turn requires detailed understanding of the torsion–rotation structures of the bands, in terms of both the line positions and intensities. The present work was therefore undertaken to expand the dataset of assigned transition line centers for CH 3 OH in the 10-lm region, and to build a base of intensity measurements for modeling of the m 8 CO-stretch band. These results have been submitted for inclusion in the upcoming edition of the HITRAN compilation of molecular line parameters [4]. The strong m 8 fundamental of CH 3 OH dominates the 10 lm spectral region, and has been intensively studied since the original work of Borden and Barker [5]. The q Supplementary data for this article are available on ScienceDirect (www.sciencedirect.com) and as part of the Ohio State University Molecular Spectroscopy Archives (http://msa.lib.ohio-state.edu/ jmsa_hp.htm). * Corresponding author. Fax: +1-506-648-5948. E-mail address: xuli@unb.ca (L.-H. Xu). 0022-2852/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jms.2004.05.017 Journal of Molecular Spectroscopy 228 (2004) 453–470 www.elsevier.com/locate/jms