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Database: Current Contents(tm) from ISI
Copyright 1992, 1995 Institute for Scientific Information, all rights reserved.
Author: WU-C-Y-R*; CHEN-F-Z
Title: VELOCITY DISTRIBUTIONS OF HYDROGEN-ATOMS AND HYDROXYL
RADICALS PRODUCED THROUGH SOLAR PHOTODISSOCIATION OF WATER
Source: JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, vol. 98, issue E4,
(APR 25, 1993) : pp. 7415-7435.
Abstract: The calculated velocity distributions of hydrogen atoms and
hydroxyl radicals produced through solar photodissociation of
gaseous water molecules are presented. Under collisionless
conditions, the calculation has been carried out using (1) the
most recently available absolute partial cross sections for the
production of H and OH through photodissociation of H2O from its
absorption onset at 1860 angstrom down to 500 angstrom, (2) the
newly available vibrational and rotational energy distributions
of both the excited and ground state OH photofragments, (3) the
calculated cross sections for the total dissociation processes,
and (4) the integrated solar flux in 10 angstrom increments from
500 to 1860 angstrom in the continuum regions and the specific
wavelength and flux at the bright solar fines, e.g., the H
Lyalpha, Lybeta, Lygamma, O VI, C III, He I. Because of the lack
of data in several dissociation processes or in certain spectral
regions, we can only obtain upper and lower bound velocity
distributions. In terms of quantum yields, the lower bound case
is set by assuming that all the undetected neutral products are
something other than H and OH fragments and an upper bound is
set by assuming the undetected neutral products am all H and OH
fragments. In terms of internal energy distributions of the OH
fragments the upper bound is set by neglecting them and a lower
bound is set by taking the available or the best estimated
values. The calculated results show that the H atoms and the OH
radicals produced exhibit multiple velocity groups. Since most
of the current cometary modeling uses a single velocity of 20
km/s associated with the photodissociation of H2O, the present
results may be uselful in interpreting the many peaks observed
in the velocity distributions of the H Lyalpha and Halpha of
comets.
Authors Abstract: N
English Abstract: Y
Language: eng
Pub. Type: REVIEW
References: 103
ISSN: 0148-0227
ISI Order #: LA444 (For ordering reprints from ISI) |
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