Isomerization of Acetonitrile N -Methylide [CH 3 CNCH 2 ] •+ and N -Methylketenimine [CH 3 NCCH 2 ] •+ Radical Cations in the Gas Phase:  Theoretical Study of the [C 3 ,H 5 ,N] •+ Potential Energy Surface (original) (raw)

1999, The Journal of Physical Chemistry A

A theoretical study of the [C 3 ,H 5 ,N] •+ potential energy surface is presented. Ab initio molecular orbital calculations at the QCISD(T)/UMP2 level with the 6-31G(d,p) basis set show that acetonitrile N-methylide [CH 3 CNCH 2 ] •+ , a •+ , and N-methylketenimine [CH 3 NCCH 2 ] •+ , b •+ , are the most stable species among the 15 isomers considered, and a heat of formation of ∆ f H°2 98 ) 970 kJ/mol is proposed for both species. Detailed examination of the [C 3 ,H 5 ,N] •+ potential energy surface indicates that a •+ , b •+ , and related isomers are stable and distinct species in the gas phase, isolated by energy barriers as high as 300 kJ/mol. Their neutral equivalent, a and b, have also been studied, thus allowing their adiabatic ionization energies to be estimated: IE a (a) ) 7.1 eV and IE a (b) ) 8.0 eV. Finally, the theoretical study of a •+ and b •+ fragmentations provides an explanation for the similarity in their high-energy CID spectra by showing a possible isomerization of these species prior to dissociation.