JPL Molecular Spectroscopy

Molecular spectroscopy is the study of absorption of light by molecules. In the gas phase at low pressures, molecules exhibit absorption in narrow lines which are very characteristic of the molecule as well as the temperature and pressure of its environment. In the microwave and long-wavelength infrared regions of the spectrum, these lines are due to quantized rotational motion of the molecule. At shorter wavelengths similar lines are due to quantized vibration and electronic motion as well as rotational motion. The precise frequencies of these lines can be fit to quantum mechanical models which can be used both to determine the structure of the molecule and to predict the frequencies and intensities of other lines. Because this absorption is so characteristic, it is very valuable for detecting molecules in the Earth's stratosphere, planetary atmospheres, and even the interstellar medium. This web site contains very specialized technical information. While the general user is welcome to browse its contents, the descriptions assume a knowledge of spectroscopy and quantum mechanics.

The JPL Molecular Spectroscopy Team supports NASA programs in Astrophysics, Atmospheric Science, and Planetary Science. Its activities include measurement of rotational lines, fitting the lines, and preparing a catalog of line positions and intensities. The members of the team include Pin Chen, Timothy J. Crawford, Brian J. Drouin, John C. Pearson, Shanshan Yu, and Keeyoon Sung, and Deacon Nemchick.

Quick Links

Guide to anonymous ftp file system for spec.jpl.nasa.gov

The sub-directory calpgm contains programs for fitting spectra. These programs are copyrighted, but made freely available as a service to the spectroscopic community. Some of the details of the program are described in H. M. Pickett, "The Fitting and Prediction of Vibration-Rotation Spectra with Spin Interactions," J. Molec. Spectroscopy 148, 371-377 (1991). Check out the on-line documentation. There is also a manuscript detailing some of the uses of the software; B. J. Drouin, "Practical Uses of SPFIT," J. Molec. Spectroscopy 340, 1-15, 2017.
The sub-directory catalog contains files related to the JPL spectral line catalog. The file catdir.cat contains the current catalog directory in a format described in the written catalog description. Line files are designated as ctttttt.cat, where tttttt is the zero-filled catalog tag number (the first entry in each line of the catdir.cat file). For example, the H atom line list is in file c001001.cat. The line files and the directory file are text files readable with usual TExt file system utilities. It is recommended that they be transferred under ftp using the ASCII option, although binary should work with UNIX hosts. The file README contains a short description of the format of catdir.cat and the catalog files. A html catalog directory is available which provides links to the catalog entries and the associated documentation (in either pdf or Tex format). The current literature reference for the catalog is H. M. Pickett, R. L. Poynter, E. A. Cohen, M. L. Delitsky, J. C. Pearson, and H. S. P. Muller, "Submillimeter, Millimeter, and Microwave Spectral Line Catalog," J. Quant. Spectrosc. & Rad. Transfer 60, 883-890 (1998).
Documentation for the fitting and predicting software, SPFIT and SPCAT can be found in spinv.pdf.
The sub-directory catalog/doc contains the documentation for the line files. Documentation for a particular species follows the line file naming convention except that the first character is 'd' rather than 'c'. These files are text files in LATeX format. The files catdoc.tex, catintro.tex, catdir.tex, and moldoc.tex are the files used to generate the catalog descriptive report. The file pretex.tex can be used to prepare a single document page. Processing the full documentation will generate a document of over 300 pages! If you have the free Adobe Acrobat reader, you can read the document catdoc.pdf . A pdf version of the introductory information about formats, etc., is available as catintro.pdf
The sub-directory catalog/pgm contains utility programs for catalog access. The subroutine set catread.f contains code for reading files into a FORTRAN program. These routines use random access, and assume that the files have a fixed line length within the file. Some modification of path names and file open options will be required for operating systems other than UNIX. The program catlist.f uses catread.f to provide listing of lines for selected molecules over a selected frequency range.
The sub-directory catalog/archive contains the some of the input files for calculating the catalog files. The page provides a directory listing with links to the archive files.

WARNING: this file system is the living repository of the JPL catalog. Recently added files may still be in a preliminary state. Caution should be used for species which have a catdir.cat line ending with '*', which have been modified since the last published edition of the catalog.