DISSOCIATIVE RECOMBINATION OF VIBRATIONALLY EXCITED H-2(- HIGH-RYDBERG-STATE FORMATION() IONS )

The dissociative recombination (DR) of vibrationally excited H-2(+) io ns to form products in high Rydberg states has been investigated exper imentally and theoretically for small (0.01 - 0.1 eV) center-of-mass e nergies of the projectile electron. The merged beam method was used in the experiment and very large cross sections were found for DR from h ighly vibrationally excited states. The Rydberg states population was analyzed by the application of an electric field ionizer with an axial electric field in excess of 70 kV/cm, which is sufficient to ionize R ydberg states with n greater than or equal to 10. Experiments with and without the ionizer were performed acid cross sections sigma(0 < n le ss than or equal to 21), sigma(n < 10), and sigma(10 less than or equa l to n less than or equal to 21) were measured. The dipole approximati on was used for the interpretation of the experimental results. Molecu lar rovibrational transitions were considered quantum mechanically. At low collision energy (0.01 eV), DR cross sections with high n = 10-21 Rydberg products arise from initial vibrational states v greater than or equal to 15. Absolute values of these cross sections are found to be of the order of magnitude of 10(-12)-10(-13) cm(2). Comparison of t heoretical and experimental results has shown that the modified back a utoionization (involving transitions to the continuum and to very high n; that is the ''indirect'' mechanism of DR) plays a significant role for all cross sections.