Competition between agostic WCH_3~+ and HWCH~+: A joint experimental and theoretical study

摘要

We present both theoretical and experimental photodissociation results on the products of the methaI:le dehydrogenation by W+ in the gas phase. We show that the reaction may lead to two isomers: whereas only the methylidenetungsten WCH~ had been proposed, we show that the hydridomethylidynetungsten HWCH+ can also be formed. Both density functional and highly correlated ab initio quantum chemical calculations have been performed using a relativistic core potential for W+ .Spin-orbit couplings have been evaluated semiempirically. We found the HWCH+ and the WCH~ isomers to be nearly degenerate, the latter structure exhibiting a strong agostic distortion. Photodissociation of the mass selected [W,C,2H] + product of the reaction has been carried out in a Fourier transform ion cyclotron resonance mass spectrometer. The H + WCH+ channel has been observed as the major photofragmentation channel and a photodissociation threshold of 2.5 +- 0.1 eV has been derived. This low-energy value is in good agreement with the thermodynamic threshold determined theoretically. These results suggest a very large bond energy associated with the triple WC bond in WCH+ (about 158 kcal/mol).