Mass spectrometric studies of trimethylindium pyrolysis

Abstract

The homogeneous decomposition of trimethylindium (TMIn) in an atmospheric pressure flow tube apparatus was studied with a time-of-flight mass spectrometer in He, D 2, and H 2 carriers. Rate constants following the expressions log k gHe( s −1)= 17.9− 54.0( kcal/mol) 2.303RT , log k gD2( s −1)= 13.4−39.8( >kcal/mol) 2.303RT , and log k gH2( s −1)= 15.0−42.6( kcal/mol) 2.303RT were determined for the three carriers. The rate constant for pyrolysis in He is comparable to that found previously for pyrolysis in a radical scavenger; consequently, TMIn predominantly decomposes by homolytic fission in He, and not by radical attack by methyl groups on the TMIn. The pyrolysis of TMIn is enhanced in D 2 and H 2 carriers, where the principal products are CH 3D and C 2H 6, and CH 4 and C 2H 6, respectively. The ratio of the products (CH 3D or CH 4) C 2H 6 in the H 2 and D 2 carriers monotically decreases with increasing temperature. TMIn pyrolysis in a 1:1 D 2:H 2 carrier shows a very low production of HD due to isotopic randomization by H and D radicals. Both the enhanced pyrolysis in H 2 and D 2, and the gas phase mass balance of carbon at all temperatures, is attributed to radical attack by H or D on TMIn. With numerical modelling techniques a novel reaction mechanism involving a short-lived hypervalent DTMIn species was tested.