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HIGH RESOLUTION SPECTRA OF THE OH STRETCHING BAND OF METHANOL

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Title: HIGH RESOLUTION SPECTRA OF THE OH STRETCHING BAND OF METHANOL
Creators: Hunt, R. H.; Lee, R. G.; Plyler, Earle K.; Dennison, D. M.
Issue Date: 1970
Abstract: The OH stretching band of methanol at 2.7 microns has been measured with a resolution of $0.02 cm^{-1}$ and recorded in digital form for deconvolution. The spectrum is complex with the greatest intensity occurring in the region around $3681 cm^{-1}$. Since the change of the electric dipole moment associated with the OH vibration has components both $\parallel$ and $\bot$ to the methyl symmetry axis, two types of rotational transitions will occur. The a-type transitions, where $\Delta K = 0$, give rise to a $\parallel$ band with P,Q and R branches and a simple calculation shows that this band should account for about 14% of the total intensity. It is probable that the broad maximum observed near $3681 cm^{-1}$ is due to this Q branch. The superimposed $\bot$ or b-type band, where $\Delta K = \pm 1$, accounts for the remaining 86% of the intensity. Since the effective moments of inertia and barrier height are not known for the excited vibrational state, the spectrum cannot be immediately determined. However, from a knowledge of the rotational energy levels of the normal state many combination differences may be accurately predicted. A number of P and R branch series have been identified in this way and the agreement is impressively good, namely several thousandths of a $cm^{-1}$ out of about $60 cm^{-1}$. Excited state values of the moments of inertia and barrier height should result from further analysis. We are indebted to Miss Y. Y. Kwan for tables of the normal state energy levels and line intensities.
URI: http://hdl.handle.net/1811/8483
Other Identifiers: 1970-N-7
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