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 electronically 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 vibrationally relaxed ions N2H+ and HCO+, two of the ions detected in interstellar gas clouds. These distributions were obtained by observing spectral emissions in the wavelength range 185-800 Mn from recombining flowing afterglow plasmas of each of these ionic species with electrons. 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. The theory is applicable to both ground and electronically excited products and can be used to predict vibrational populations of ground state 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 suggests additional developments and tests that should be applied to the theory before it is used more generally for the problem of interstellar molecular synthesis.