Ion-Molecule Complexes in 1,2-Alkyl Shifts

2016

J. Phys. Chem. A

The ability to selectively control chemical reactions related to biology, combustion, and catalysis has recently attracted much attention. In particular, the hydrogen atom relocation may be used to manipulate bond-breaking and new bond-forming processes and may hold promise for far-reaching applications. Thus, the hydrogen atom migration preceding fragmentation of the gas-phase pyridine molecules by the H(+), H2(+), He(+), He(2+), and O(+) impact has been studied experimentally in the energy range of 5-2000 eV using collision-induced luminescence spectroscopy. Formation of the excited NH(A(3)Π) radicals was observed among the atomic and diatomic fragments. The structure of the pyridine molecule is lacking of the NH group, therefore observation of its A(3)Π → X(3)Σ(-) emission bands is an evidence of the hydrogen atom relocation prior to the cation-induced fragmentation. The NH(A(3)Π) emission yields indicate that formation of the NH radicals depends on the type of selected projectile and can be controlled by tuning its velocity. The plausible collisional mechanisms as well as fragmentation channels for NH formation in pyridine are discussed.

Section: Resultsmentioning

confidence: 57%

Section: Resultsmentioning

confidence: 99%

Observation of the Hydrogen Migration in the Cation-Induced Fragmentation of the Pyridine Molecules

2016

J. Phys. Chem. A

“…But why is it so prevalent at such low velocities? Experimentally, such an increase is an indication that transient complex formation may be taking place. , In the past decades considerable experimental and theoretical investigations have demonstrated that ion-neutral molecule complexes are ubiquitous intermediates in the gas-phase reactions. − The corresponding ion–molecule components remain bound together by ion–dipole attraction and may react with each other by hydrogen transfer . We therefore hypothesize that rapid enhancement of the fragmentation yield of the CH(A 2 Δ) may be a signature of a mechanism proceeding through intermediate [C–C 4 H 8 O] + complex formation prior to dissociation.…”

Section: Resultsmentioning

confidence: 95%

Fragmentation of Tetrahydrofuran Molecules by H⁺, C⁺, and O⁺ Collisions at the Incident Energy Range of 25–1000 eV

2015

J. Phys. Chem. A

We have studied fragmentation processes of the gas-phase tetrahydrofuran (THF) molecules in collisions with the H(+), C(+), and O(+) cations. The collision energies have been varied between 25 and 1000 eV and thus covered a velocity range from 10 to 440 km/s. The following excited neutral fragments of THF have been observed: the atomic hydrogen H(n), n = 4-9, carbon atoms in the 2p3s (1)P1, 2p4p (1)D2, and 2p4p (3)P states and vibrationally and rotationally excited diatomic CH fragments in the A(2)Δ and B(2)Σ(-) states. Fragmentation yields of these excited fragments have been measured as functions of the projectile energy (velocity). Our results show that the fragmentation mechanism depends on the projectile cations and is dominated by electron transfer from tetrahydrofuran molecules to cations. It has been additionally hypothesized that in the C(+)+THF collisions a [C-C4H8O](+) complex is formed prior to dissociation. The possible reaction channels involved in fragmentation of THF under the H(+), C(+), and O(+) cations impact are also discussed.

“…The appearance of the narrow resonances in the H( n ), CH(A 2 Δ, B 2 Σ + ) and C 2 (d 3 Π g ) cross sections seems to point at the formation of the ion-neutral molecule temporary complexes prior to dissociation [51,52]. Experimental and theoretical investigations show that such complexes are essential intermediates in many gas-phase reactions including collisions [51,52,63,64,65,66,67]. These studies showed that in collisional systems both interacting components are bound collectively by the ion-dipole electrostatic attraction.…”

Section: Resultsmentioning

confidence: 99%

Charge Transfer, Complexes Formation and Furan Fragmentation Induced by Collisions with Low-Energy Helium Cations

Łabuda

2019

IJMS

The present work focuses on unraveling the collisional processes leading to the fragmentation of the gas-phase furan molecules under the He+ and He2+ cations impact in the energy range 5–2000 eV. The presence of different mechanisms was identified by the analysis of the optical fragmentation spectra measured using the collision-induced emission spectroscopy (CIES) in conjunction with the ab initio calculations. The measurements of the fragmentation spectra of furan were performed at the different kinetic energies of both cations. In consequence, several excited products were identified by their luminescence. Among them, the emission of helium atoms excited to the 1s4d 1D2, 3D1,2,3 states was recorded. The structure of the furan molecule lacks an He atom. Therefore, observation of its emission lines is spectroscopic evidence of an impact reaction occurring via relocation of the electronic charge between interacting entities. Moreover, the recorded spectra revealed significant variations of relative band intensities of the products along with the change of the projectile charge and its velocity. In particular, at lower velocities of He+, the relative cross-sections of dissociation products have prominent resonance-like maxima. In order to elucidate the experimental results, the calculations have been performed by using a high level of quantum chemistry methods. The calculations showed that in both impact systems two collisional processes preceded fragmentation. The first one is an electron transfer from furan molecules to cations that leads to the neutralization and further excitation of the cations. The second mechanism starts from the formation of the He−C4H4O+/2+ temporary clusters before decomposition, and it is responsible for the appearance of the narrow resonances in the relative cross-section curves.