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Bull.
SOC. Chim. Belg. vo1.92/n010/1983
ELECTRIC
DIPOLE MOMENT
1
N. Grevesse
,
FUNCTION OF
A.J.
OH
FROM
THE
SOLAR
SPECTRUM
Sauvall and E.F. Van Dishoeck3
'Institut d'Astrophysique, Universite de Lihge, B-4200 Cointe-OugrBe
20bservatoire Royal de Belgique, av. Circulaire, 3, 1180 Bruxelles
3Sterrewacht Leiden, Huygens Laboratorium, NL-2300 RA Leiden
Presented at the XVIth International Symposium of Free Radicals
September 12-16,1983,Lauzelle-Ottignies,Belgium
High resolution solar spectra with a large signal to noise ratio have been
recorded between 760 and 970 cm-l at the McMath Solar Telescope of the Kitt
Peak National Observatory. The Fourier-transform spectrometer can reach a 1 m
path difference and so is capable of resolution up to 0.005 cm-l (see [l}).
About 100 unblended OH absorption lines of the pure rotational spectrum
relative to the v=O, 1, 2 and 3 levels of the X 2n state have been measured on
two different spectra. The present investigation is an extension of other
works limited to lines of the V=O level I2). Most of the OH lines were not yet
observed in the laboratory; so it appeared necessary to predict line positions
from molecular constants derived by Goldman et al. I31 on the basis of available solar and laboratory data. The observed rotation lines are of: rather high
excitation potential (between 9000 and 28000 cm-l) and belong to the first four
vibrational levels : v = 0 (N=22 to 31), v = 1 (N=24 to 34), v = 2 (N=26 to 3 7 )
and v = 3 (N=27 to 32).
Theoretical profiles have been calculated for all solar OH lines adopting
a good representative photosperic model and the same abundance of oxygen. The
transition probabilities of pure rotation lines are directly proportional to
the square of a matrix element with the electric dipole moment function. Meerts
and Dymanus {4} have measured very accurately the dipole moment f o r v=O, J=9/2
2
~,~
? 0.0009 Debye).
No other experimental determinations exist
of X I I(1.6676
for higher values of v and/or N, but a large variety of theoretical results are
available { 5 } . The matrix element for each line has been calculated using different dipole moment functions and an empirical RKR potential function.
From a comparison between observed and theoretical profiles for all selected solar lines, we conclude that the dipole moment function recently calculated by Werner et a1 I 5 1 leads to the best agreement with our solar data.
Other moment functions, like that found by Chu et al. { 5 1 , would give a slight
dependence of the oxygen solar abundance with the excitation potential, which
is an unacceptable result.
The present investigation shows that the solar spectrum may bring important information about experimental or theoretical results in molecular spectroscopy. Very accurate solar data have permitted to make a trial among several proposed dipole moment functions.
Detailed results have been suhmitted for publication {61.
-
a45
-
1. J.W. Brault, Proceedings of the J . O . S . O .
Workshop "Future Solar Optical
Need and Constraints", Oss. Mem. Arcetri 106, 33 (1978).
Observations
A. Goldman, F . J . Murcray, J.R. Gillis and D.G. Murcray, Astrophys. J.
(letters) 248, L133 (1981).
A. Goldman, D.G. Murcray, D.L. Lambert and J.F. Dominy, Mon. Not. Roy.
Astr. SOC. 203, 767 (1983).
A. Goldman, J.R. Gillis and J.A. Coxon, J.Q.S.R.T. 29, 469 (1983).
W.L. Meerts and A. Dymanus, Chem. Phys. Lett. 23, 45 (1973).
W.J. Stevens, G. Das, A.C. Wahl, M. Krauss and D. Neumann, J. Chem. Phys.
61, 3686 (1974).
S.-I. Chu, M. Yoshimine and B. Liu, J. Chem. Phys. 61, 5389 (1974).
W. Meyer and P. Rosmus, J. Chem. Phys. 63, 2356 (1975).
S.R. Langhoff, E.F. Van Dishoeck, R. Wetmore and A . Dalgarno, J. Chem. Phys.
-
2.
3.
4.
5.
77,
1379 (1982).
H . 4 . Werner, P. Rosmus and E.-A. Reinsch, J. Chem. Phys. 2, 905 (1983).
6. A.J. Sauval, N. Grevesse, J.W. Brault, G.M. Stokes and R. Zander, Astrophys.
J. (submitted).
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846
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