Measurements of dissociative recombination coefficients of H+3, HCO+, N2H+, and CH+5at 95 and 300 K using the FALP apparatus

摘要

Meaurements are presented of the dissociative recombination coefficients agr;tfor reactions of electrons with H+3, D+3, HCO+, DCO+, N2H+, N2D+, and CH+5ions at 95 and 300 K. The measurements were made under truly thermalized conditions using a flowing afterglow (FALP) apparatus. Contrary to previous stationary afterglow (SA) studies, agr;t(H+3) was found to be immeasurably small lsqb;lsim;2 (minus;8) cm3thinsp;sminus;1rsqb; at both temperatures which is consistent with recent theoretical predictions. However some evidence was obtained indicating that vibrationally excited H+3recombined efficiently, which is also in accordance with the recent theory. At 300 K, agr;t(HCO+)=1.1 (minus;7) cm3thinsp;sminus;1and agr;t(N2H+)=1.7 (minus;7) cm3thinsp;sminus;1and both were larger by a factor of three at 95 K. agr;t(CH+5) =1.1 (minus;6) cm3thinsp;sminus;1at 300 K and 1.5 (minus;6) cm3thinsp;sminus;1at 95 K. The agr;t(HCO+) data are compared with previous SA data and the agr;t(N2H+) and agr;t(CH+5) data are discussed in relation to the recombination coefficients agr;e(N2H+) and agr;e(CH+5) derived from merged beam (MB) cross section data. Stressed throughout the paper is the need to appreciate the chemical and physical processes which can occur in the afterglow and which may distort agr;tdeterminations. Tentative explanations are given for the differing values of agr;tand agr;eobtained from FALP, SA, and MB experiments.