Time Resolved Properties of Small Astrophysical Molecules

Abstract

Periodic excitations of molecular levels makes possible not only the determination of resulting emission lines but also their individual lifetimes. Today most measurements of this kind are performed either using high power electron excitation, such as applied in the High Frequency Deflection (HFD) technique developed at our laboratory, or pulsed laser excitation. Completed by for instance supersonic jet targets, time resolved spectroscopy should now be considered as an important branch of molecular physics with a number of astrophysical applications.

While most astrophysical observations of molecules have recently been carried out at radio wavelengths, the most accurate abundance estimates are generally performed from optical absorption spectra provided that the associated f-values are known. Thanks to the development of time resolved spectroscopy, f-values are now available for transitions in most of the important diatomic molecules, which combined with equivalent widths may yield abundances with uncertainties as small as 15 %.

Other important applications of molecular lifetime investigations are found in studies of various kinds of radiationless transitions, for which purpose it is much more sensitive than classical spectroscopic tools. Thus the inverse of our recently discovered new kind of predissociations through direct interaction between bound-continuum levels of two attractive states in the carbon group of hydrides could be important at molecular formation at low temperatures. Other applications are found in determinations of, for instance thermal collision cross sections and various kinds of rate coefficients.