New flowing afterglow technique for determining products of dissociative recombination: CH5+ and N2H+

There are discrepancies in the literature for the product distributions of electron-ion (e-i) recombination when determined using different techniques. Because of this, a new technique has been developed. This is based on the flowing afterglow, with the product neutrals detected by electron impact ionization followed by mass spectrometric detection. However, in addition to the products of recombination, there are neutrals present from ion-molecule reactions and from the gases introduced into the flow tube to create the ion of interest, which often have much greater concentrations than the products. To distinguish these products, an electron attaching gas is pulsed into the flow to transiently attach the electrons, thus quenching e-i recombination. Then the difference between the attaching gas in and out yields the product distribution. Recombination products have been detected even when their signal is as much as similar to 10(4) less than background. Here the details of the technique are described and the possible sources of error discussed. The viability of the technique is illustrated for the recombinations of CH5+ and N2H+. The latter establishes the major product as N-2 + H (95 to 100%) correcting an error in the literature. In the former case, the major channel detected is CH4 + H (95%) which is in disagreement with a storage ring (SR) result which gave CH3 as the major channel (68%). Possible reasons for this are discussed.