Quantum Deconstruction of the Infrared Spectrum of CH5+
Xinchuan Huang,1
Anne B. McCoy,2*
Joel M. Bowman,1*
Lindsay M. Johnson,2
Chandra Savage,3
Feng Dong,3
David J. Nesbitt3*
We present two quantum calculations of the infrared spectrum
of protonated methane (CH
5+) using full-dimensional, ab initio–based
potential energy and dipole moment surfaces. The calculated
spectra compare well with a low-resolution experimental spectrum
except below 1000 cm
–1, where the experimental spectrum
shows no absorption. The present calculations find substantial
absorption features below 1000 cm
–1, in qualitative agreement
with earlier classical calculations of the spectrum. The major
spectral bands are analyzed in terms of the molecular motions.
Of particular interest is an intense feature at 200 cm
–1,
which is due to an isomerization mode that connects two equivalent
minima. Very recent high-resolution jet-cooled spectra in the
CH stretch region (2825 to 3050 cm
–1) are also reported,
and assignments of the band origins are made, based on the present
quantum calculations.
2 Department of Chemistry, The Ohio State University, Columbus, OH 43210, USA.
3 JILA, National Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309–0040, USA.
* To whom correspondence should be addressed. E-mail: mccoy{at}chemistry.ohio-state.edu (A.B.M.); jmbowma{at}emory.edu (J.M.B.); djn{at}jila.colorado.edu (D.J.N.)
