A comparative theoretical study of the reactivities of the Al + and Cu + ions toward methylamine and dimethylamine

A very recent laser ablation‐molecular beam experiment shows that an Al + ion can react with a single methylamine (MA, CH 3 NH 2 ) or dimethylamine (DMA, (CH 3 ) 2 NH) molecule to form a 1:1 ion–molecule complex Al + [CH 3 NH 2 ] or Al + [(CH 3 ) 2 NH)], whereas a dehydrogenated complex ion Cu + [CH 3 N] or Cu + [C 2 H 5 N] is detected, respectively, in the similar reaction for a Cu + ion. Here, we show a comparative density functional theory study for the reactivities of the Al + and Cu + ions toward MA and DMA to reveal the intrinsic mechanism. It is found that the interactions of the Al + ion with MA and DMA are mostly electrostatic, leading to the direct ion–molecule complexes, Al + NH 2 CH 3 and Al + NH( CH 3 ) 2 , in contrast to the non‐negligible covalent character in the corresponding Cu + ‐containing complexes, Cu + NH 2 CH 3 and Cu + NH( CH 3 ) 2 . The general dehydrogenation mechanism for MA and DMA promoted by the Cu + ion has been shown, and the preponderant structures contributing to the mass spectra of the product ions Cu + [CH 3 N] and Cu + [C 2 H 5 N] are rationalized as Cu + NHCH 2 and Cu + N( CH 2 )( CH 3 ). The presumed dehydrogenation reactions are also discussed for the Al + ‐containing systems. However, the involved barriers are found to be too high to be overcome at low energy conditions. These results have rationalized all the experimental observations well. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010