Computer program predicts the spectra resulting from electronic transitions of diatomic molecules and atoms in local thermodynamic equilibrium. The program produces a spectrum by accounting for the contribution of each rotational and atomic line considered

Arnold, J. O.

Lyle, G. C.

Whiting, E. E.

English

NASA Technical Reports Server

July 1969	 Brief 69-10232 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
A Computer Program for a Line-By-Line Calculation of Spectra from

Diatomic Molecules and Atoms Assuming a Voigt Line Profile 
fl
The problem: 
The task of computing a reasonably accurate spec-
trum for a mixture of atoms and diatomic molecules 
is complicated by the enormously large number of 
rotational lines forming the spectrum. In addition, 
several kinds of electronic transitions may be involved, 
eaéh with its own required set of line strength and 
wavelength equations. These considerations make it 
impractical to produce the band spectra from even a 
simple diatomic transition without the aid of an elec-
tronic computer. 
The solution: 
A computer program for predicting the spectra 
resulting from electronic transitions of diatomic mole-
cules and atoms in local thermodynamic equilibrium. 
How it's done: 
The program produces a spectrum by accounting 
for the contribution of each rotational and atomic line 
considered. The integrated intensity of each line is 
distributed in the spectrum by an approximate Voigt 
profile. The program can produce spectra for optically 
thin gases or for cases where simultaneous emission 
and absorption occur. In addition, the program can 
compute the spectrum resulting from the absorption 
of incident radiation by a column of cold gas or the 
high-temperature, self-absorbed emission spectrum 
from a nonisothermal gas. The computed spectrum 
can be output directly or combined with a slit function 
and sensitivity calibration to predict the output of a 
grating spectrograph or a fixed wavelength radiometer. 
Specifically, the program has the capability to in-
clude the following features in any computation:
I) Parallel transitions (AA = A'-A'' = 0), in which 
spin splitting and lambda doubling are ignored (ignor-
ing spin splitting and/or lambda doubling means that 
the total rnultiplet strength is assumed to reside in a 
single "effective" line). 
2) Perpendicular transitions (A= * I), in which spin 
splitting and lambda doubling are ignored. 
3) transitions, in which lambda doubling is 
ignored. 
4) Atomic lines. 
5) Option to terminate rotational-line calculations 
when the molecule dissociates due to rotation. 
6) Option to include the alternation of line inten-
sities for homonuclear molecules. 
7) Use of an approximate Voigt profile for the line 
shape.
8) Radiation energy transport in a nonisothermal 
gas. 
The output options available in the program are: 
(I) Tabulation of the spontaneous-emission spectrum 
(i.e., optically thin spectrum) for a 1.0 cm path length, 
(2) Tabulation of the "true" spectrum, which incorpo-
rates spontaneous emission, induced emission, absorp-
tion, and externally incident radiation through the 
equation of radiative transfer, (3) Tabulation of the 
curve of growth for an arbitrary number of wave-
length intervals, (4) Tabulation of the integrated 
intensity over an arbitrary number of wavelength 
intervals and (5) Tabulation of the output signal pro-
duced by a radiometer or spectrometer by specifying 
an instrument calibration. The instrument slit function 
can be approximated by up to 99 straight-line segments 
or by a Gaussian curve. The computation can be made 
at a fixed wavelength to simulate a radiometer or by 
(continued overkal) 
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https://ntrs.nasa.gov/search.jsp?R=19690000232 2020-03-16T17:46:07+00:00Z
scanning across any specified wavelength interval to 
simulate a grating instrument. In the latter case, the 
sensitivity can be varied as a function of wavelength 
to accurately simulate a grating-instrument calibration. 
Notes: 
I. This program . should be of interest to personnel in 
the field of quantitative spectroscopy. The program 
predicts, the spectra resulting from electronic transi-
tions of diatomic molecules and atoms in local ther-
modynamic equilibrium. 
2. This program is written in FORTRAN IV for use on 
the IBM 7040/7094 DCS.
3. Inquiries should be made to: 
COSMIC 
Computer Center 
University of Georgia 
Athens, Georgia 30601 
Reference: B69-10232 
Patent status: 
No patent action is contemplated by NASA. 
Source: Ellis E. Whiting, James 0. Arnold, 
and Gilbert C. Lyle 
Ames Research Center 
(ARC-l022 1)
C 
Brief 69-10232	 Category 06


A computer program for a line-by-line calculation of spectra from diatomic molecules and atoms assuming a Voight line profile

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