Further Resolution of Two Parallel Bands of Ammonia and the Interaction between Vibration and Rotation

Hsi-yin Sheng, E. F. Barker, and D. M. Dennison
Phys. Rev. 60, 786 – Published 1 December 1941
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Abstract

The fundamental low frequency parallel band at 10μ and its upper stage band at 16μ have been re-examined under high dispersion. It is found that most of the fine structure lines hitherto reported as single are resolved into multiplets. The positions of the lines may be accounted for accurately by assuming that the energy levels have the form, Ws,ahc=WVs,ahc+AVs,a(J2+JK2)+CVs,aK2+F(JK). The superscripts s or a indicate whether the level in question is the lower or the upper of the two levels produced by the double minimum potential. F(JK) is the small centrifugal distortion term calculated by Slawsky and Dennison. The constants A0s, A0a, A1s, A1a, A2s, C1sC0a and C1aC0s are determined from the experimental data. The following vibrational energies are also found, W1s=932.24hc, W1a=968.08hc and W2s=1597.4hc.

In the discussion of the rotational constants, it is pointed out that two quantities are involved, (a) the average constants, averaged over the two levels of the double minimum, as 12(Avs+Ava), and (b) the difference of the constants, as AvaAvs. Recently Shaffer has calculated the theoretical expressions for the averaged constants and has shown how these depend upon the anharmonic terms in the potential energy. A treatment of the difference of the constants is equivalent to a treatment of the change in the splitting of the two levels of the double minimum due to the vibration-rotation interaction. This may be computed from the expression for the splitting of the double minimum levels given by the W-K-B method of approximation. The calculated result for the change in splitting of the first vibration levels is (δΔhc)theo=0.162(J2+J)+0.222K2, which is in excellent agreement with the observed change (δΔhc)exp=0.17(J2+J)+0.23K2. The significance of the agreement is discussed.

  • Received 9 October 1941

DOI:https://doi.org/10.1103/PhysRev.60.786

©1941 American Physical Society

Authors & Affiliations

Hsi-yin Sheng, E. F. Barker, and D. M. Dennison

  • Harrison M. Randall Laboratory of Physics, University of Michigan, Ann Arbor, Michigan

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Issue

Vol. 60, Iss. 11 — December 1941

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