INTERFERENCE EFFECTS IN THE INFRARED SPECTRUM OF HD
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Date
1984
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Publisher
Ohio State University
Abstract
Interference between the small permanent dipole moment of HD and the dipoles induced during collisions with other molecules causes strange effects in the spectrum. The dipole P- and R- branch lines show asymmetric (Fano) line shapes, as well as anomalous intensities which vary with $pressure.^{1-6}$ We have performed a new series of experiments on the fundamental $(\approx 3700 cm)$ and pure rotational (far-infrared) bands for both pure HD and HD-rare gas mixtures. The results reconcile the apparently contradictory earlier observations of $destructive^{1, 3, 6}$ and $constructive^{2}$ interference: in all the cases we have analyzed so far, there is initial destructive interference proportional to the density squared (and due to intracollisional effects), and, at higher pressures, eventual constructive interference proportional to the density cubed (and due to intercollisional effects). The theoretical formulation of Herman al.$^{4,5}$ is strikingly confirmed, but no predictions are yet available for the actual values of the (``phase shift'') parameters which we derive experimentally, and particularly for their variation with perturbing gas and with HD transition.
Description
$^{1}$ A.R.W. McKellar, Can. J. Phys. 51, 389 (1973). $^{2}$ J.D. Poll, R.H. Tipping, R.D.G. Prasad, and S.P. Reddy, Phys. Rev. Lett. 36, 248 (1976). $^{3}$ R.H. Tipping, J.D. Poll, and A.R.W. McKellar, Can. J. Phys. 56, 75 (1978). $^{4}$ R.M. Herman, Phys. Rev. Lett. 42, 1206 (1979). $^{5}$ R.M. Herman, R.H. Tipping, and J.D. Poll, Phys. Rev. A 20, 2006 (1979). $^{6}$ J.B. Nelson and G.C. Tabisz, Phys. Rev. A 28, 2157 (1983).
Author Institution: Herzberg Institute of Astrophysics, National Research Council of Canada; Department of Physics, Memorial University of Newfoundland, St. John's
Author Institution: Herzberg Institute of Astrophysics, National Research Council of Canada; Department of Physics, Memorial University of Newfoundland, St. John's