Gas‐phase ion–molecule reactions in dilute mixtures of dimethyl ether in krypton. Bimolecular and clustering reactions

The results of high‐pressure variable‐temperature and variable ionizing electron energy studies of gas‐phase ion‐molecule reactions of dimethyl ether in krypton are presented. Near the ionization threshold a series of peaks corresponding to (CH 3 OCH 3 ) n H + ( n = 1‐4) clusters are observed. At higher ionizing electron energies, two new series of peaks appear, corresponding to [CH 3 OCH 2 ] + (CH 3 OCH 3 ) n and [(CH 3 ) 3 O] + (CH 3 OCH 3 ) n clusters. The onium ion, [(CH 3 ) 3 O] + , has been previously reported at elevated temperatures under methane chemical ionization conditions. It was suggested that the onium ion is formed by reaction of (CH 3 ) 2 OH + with CH 3 OCH 3 with subsequent elimination of methanel, i.e. by fragmentation of an adduct ion. The present results strongly suggest that, under our conditions, [CH 3 OCH 2 ] + rather than thermal (CH 3 ) 3 OH + , is the precursor to [(CH 3 ) 3 O] + .