Electronic state dependence of the ion–molecule reaction CH3CN+ + CH3CN → CH4CN+ + CH2CN: threshold electron–secondary ion coincidence (TESICO) and direct ab initio molecular dynamics study

Abstract

The ion-molecule reaction, CH(3)CN(+) + CH(3)CN → CH(3)CNH(+) + CH(2)CN, has been investigated using the threshold electron-secondary ion coincidence (TESICO) technique. Relative reaction cross sections for two microscopic reaction mechanisms, i.e., proton transfer (PT) from the acetonitrile ion CH(3)CN(+) to neutral acetonitrile CH(3)CN and hydrogen atom abstraction (HA) by CH(3)CN(+) from CH(3)CN, have been determined for two low-lying electronic states, (2)E and (2)A(1) of the CH(3)CN(+) primary ion. The cross section for PT of the (2)A(1) state was smaller than that of the (2)E state, whereas that of HA are almost the same in the two states. Ab initio calculations showed that the dissociation of the C-H(+) bond of CH(3)CN(+) is easier in the (2)E state than that in the (2)A(1) state. The direct ab initio molecular dynamics (MD) calculations showed that two mechanisms, direct proton transfer and complex formation, contribute the reaction dynamics.

Structure, Stability, and Spectroscopic Properties of Small Acetonitrile Cation Clusters

“…Both structures are characterized by having linear backbones, with N–H distances in-between 1.23 and 1.29 Å. The (CH 3 CN)­CH 2 CNH + structure was also obtained by Tachikawa and co-workers at the MP2/6-311++G­(d,p) and QCISD/6-311++G­(d,p) levels of theory . Furthermore, the optimized (CH 3 CN) 2 H + structure has D 3 d symmetry.…”

“…The (CH 3 CN)CH 2 CNH + structure was also obtained by Tachikawa and co-workers at the MP2/6-311++G(d,p) and QCISD/ 6-311++G(d,p) levels of theory. 55 Furthermore, the optimized (CH 3 CN) 2 H + structure has D 3d symmetry. Both clusters are held together by the formation of hydrogen bonds.…”

“…For a better understanding and interpretation of experimental data, quantum chemistry methods are often applied. − In particular, for acetonitrile, previous theoretical investigations focused on high order molecular clusters stabilized by intermolecular interactions − and formation of cationic clusters and dissociation pathways, − as well as formation of anionic clusters …”

Selective Generation of the Radical Cation Isomers [CH3CN]•+ and [CH2CNH]•+ via VUV Photoionization of Different Neutral Precursors and Their Reactivity with C2H4

“…By exploiting the different reactivity of the two tautomers with ethylene (that it is known to be unreactive with [CH 2 CNH] •+ but to give exothermic charge exchange and proton transfer reactions with [CH 3 CN] •+ ) using the reaction monitoring technique in a guided ion beam tandem mass spectrometer, we have demonstrated that photoionization of CH 3 CN below 12.8 eV produces solely the [CH 3 CN] •+ isomer, and the [CH 2 CNH] •+ tautomer will start being populated at photon energies above the isomerization threshold. It has been proposed that, using the TESICO (threshold electron secondary ion coincidence spectroscopy) technique, the ground and first electronically excited states of [CH 3 CN] •+ ion are selectively generated at different photon energies. However, our study demonstrates that, at the energy required to populate the excited 2 A 1 state, the isomerization channel into [CH 2 CNH] •+ is also open, thus posing some uncertainty in the possibility to generate a pure beam of electronically excited [CH 3 CN] •+ .…”

Low-Temperature Branching Ratios for the Reaction of State-Prepared N2+with Acetonitrile

“…17,18 The dipole moment of CH 3 CN(A 1 ), CH 3 CN + ( 2 E), and CH 3 CN + ( 2 A 1 ) are 3.89, 2.58, and 0.02 D, respectively. 16 Since the interaction energy of an ionÀmolecule reaction involving a polar molecule is strongly influenced by the dipole moments, 19 the vanishing dipole moment associated with the 2 A 1 state leads to a corresponding decrease in the reaction cross section for this state as compared with the more dipolar 2 E state. In addition, ionÀmolecule reactions are relatively disadvantageous for the 2 A 1 state, since the CÀH bond of CH 3 CN + ( 2 E) is weaker than that of CH 3 CN + -( 2 A 1 ).…”