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WORKING GROUP 5: MOLECULAR STRUCTURE AND TRANSITION DATA

E.F. van Dishoeck, Chair
Leiden Observatory
P. O. Box 9513
2300 RA Leiden
The Netherlands

The most significant development in the last three years has been the enormous expansion and availability of atomic and molecular databases in electronic form (CD-ROM, ftp, $World-Wide-Web).$ 1-5$Millions\; of\; molecular\; lines\; ranging\; from\; the\; millimeter\; to\; the\; extreme\; ultraviolet\; part\; of\; the\; spectrum\; can\; now\; be\; accessed\; on-line,\; and\; improved\; software\; allows\; rapid\; searches\; through\; the\; data\; bases.\; At\; the\; same\; time,\; the\; astrophysical\; needs\; for\; such\; large\; data\; bases\; have\; increased\; considerably.\; Spectral\; line\; surveys\; at\; submillimeter\; wavelengths\; typically\; contain\; thousands\; of\; rotational$ lines,$ 6$high\; resolution\; infrared\; spectra\; from\; the\; ground\; and\; the$$Infrared Space Observatory require large amounts of information on the vibrational $transitions,$ 7,8$whereas\; large\; format\; CCDs\; in\; the\; optical\; and\; ultraviolet\; allow\; large\; wavelength\; ranges\; to\; be\; scanned\; for\; electronic\; transitions.\; The\; astrophysical\; modeling\; has\; improved\; to\; the\; stage\; that\; highly\; accurate\; molecular\; data\; are\; essential.\; A\; well-known\; example,\; which\; has\; been\; studied\; intensively\; by\; several\; groups\; over\; the\; last\; decade,\; is\; provided\; by\; the\; VUV\; electronic\; transitions\; of$ CO.$ 21,31$For\; models\; of\; cool\; stars\; and\; brown\; dwarfs,\; information\; on\; the\; weaker\; transitions,\; whose\; intensities\; are\; five\; orders\; of\; magnitude\; less\; than\; those\; of\; the\; strongest\; transitions,\; proves\; to\; be$ essential.$ 9$$$$

There have been significant developments in the experimental techniques and theoretical methods for determining molecular structure, both of stable species, and of radicals and ions. Of particular interest is the progress in measuring and calculating the spectra of large molecules, including PAH's, long carbon chains and $C$ $$₆₀.

The following summary is based on contributions sent to me by U.G. Jørgenson, T. Oka, J.P. Phillips, F. Rostas, P.L. Smith, and P. Thaddeus in the summer of 1996. Other topics have been added through a literature search. This report focuses on the highlights, and concerns only molecules of astrophysical interest. No attempt has been made to provide a complete overview or list of references. For further information on a specific molecule, the bi-monthly Berkeley Newsletter continues to be a good starting point. The printed Newsletter is essentially a bibliography of articles in the current journals on molecules comprising four or fewer atoms (contact jphillips@astro.berkeley.edu or spdavis@physics.berkeley.edu).

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