VIBRATIONAL-EXCITATION IN THE PRODUCTS OF ELECTRON-ION RECOMBINATION - A TEST OF THEORY FOR IONS OF INTERSTELLAR SIGNIFICANCE

Vibrational population distributions have been obtained for the electr onically excited states N-2((BIIg)-I-3), v = 2-9, and CO(a(3)II(r)), v = 0-6, produced in the dissociative electron recombination of the vib rationally relaxed ions N2H+ and HCO+, two of the ions detected in int erstellar gas clouds. These distributions were obtained by observing s pectral emissions in the wavelength range 185-800 Mn from recombining flowing afterglow plasmas of each of these ionic species with electron s. The experimental data have been compared with the recent theory of Bates in which contributions to vibrational excitation in the products due to the impulse force of the dissociation and to the ''relic'' of the normal vibrational modes of the recombining ion were considered. T he theory is applicable to both ground and electronically excited prod ucts and can be used to predict vibrational populations of ground stat e species, the radiative relaxation of which should be detectable from interstellar clouds, although this may be below the detection limits of current instrumentation. The degree of agreement between theory and experiment shows that this theoretical approach is promising and sugg ests additional developments and tests that should be applied to the t heory before it is used more generally for the problem of interstellar molecular synthesis.