Effects of zero point vibration on the reaction dynamics of water dimer cations following ionization

2020

J. Phys. Chem. A

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Ammonia cluster cations are a chemical species that has recently attracted considerable research attention as an ion−molecule reaction species in the planetary atmosphere, surface reaction species in materials chemistry, and super-alkali species. Reactions of the radical cation of an ammonia cluster, [(NH 3 ) n ] + (n = 2−6), following the ionization of the parent neutral cluster, were investigated using direct ab initio molecular dynamics to elucidate the reactions of the ammonia cluster cation under astrochemical conditions. The calculations showed that two competing reaction channelsproton transfer (PT) channel and complex formation channeloperate after the ionization of neutral clusters. In the PT channel, a proton of NH 3 + was transferred to a neighboring ammonia molecule. The PT channel was found in all clusters (n = 2−6). Reaction via the PT channel became faster with increasing cluster size and saturated around n = 5− 6. In the complex formation channel, a face-to-face complex having a H 3 N−NH 3 + structure (with a N−N bond) was formed. This channel was found only in larger clusters (n = 5−6). Time scales of PT and complex formation channels were calculated to be 20− 30 and 40−50 fs, respectively. The reaction mechanism was discussed based on the results of theoretical calculations.

Section: Computational Detailsmentioning

confidence: 99%

Intramolecular Reactions in Ionized Ammonia Clusters: A Direct Ab Initio Molecular Dynamics Study

2020

J. Phys. Chem. A

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“…To examine the effects of the initial structure on the reaction dynamics, geometries were generated near the equilibrium point using zero-point vibration (ZPV) 39 or direct AIMD calculations under a constant temperature condition (10 K), 40 which is expressed as 10 K simulation. From the ZPV calculation (MP2/6-311++G(d,p) level), a total of ten geometrical configurations were selected and direct AIMD calculations were performed for the cluster cations.…”

Section: Calculation Methodsmentioning

confidence: 99%

Activation of CO₂ in Photoirradiated CO₂–H₂O Clusters: Direct Ab Initio Molecular Dynamics (MD) Study

2019

J. Phys. Chem. A

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Carbon dioxide (CO2) is one of the stable and inactive molecules that contribute to greenhouse gases. The development of new reactions of CO2 activation, chemical fixation, and conversion is a very important issue. In this report, the reactions of CO2–H2O binary clusters were investigated using a direct ab initio molecular dynamics (AIMD) method to find a new reaction of CO2 activation. Clusters composed of carbon dioxide and water molecules, CO2(H2O) n (n = 2–5), were utilized as a model of the binary cluster. The reaction dynamics of [CO2(H2O) n ]+ following the ionization of parent neutral clusters were also investigated. Two electronic states of [CO2(H2O) n ]+ were examined for direct AIMD surfaces: CO2[(H2O) n ]+ (ground state) and (CO2)+(H2O) n (excited charge transfer (CT) state). After the ionization of the clusters, a proton-transfer (PT) reaction occurred within the (H2O) n + moiety at the ground state, whereas the reactive HCO3 radical was formed at the CT state for OH addition to CO2 +: CO2 +(H2O) n → HCO3 + H+(H2O) n−1. The mechanisms of the PT process and the HCO3 radical formation were discussed based on the theoretical results.

“…To investigate the effect of the initial structures on the reaction mechanism and time-scale of stacking formation in (Bz) 2 + and (Bz) 2 + -H 2 O, the initial geometries were generated by direct AIMD calculations under a constant temperature condition 28,29 . The temperature was chosen as 10 K. First, direct AIMD calculations of the neutral systems, (Bz) 2 and (Bz) 2 -H 2 O, were carried out at the CAM-B3LYP/6-311++G(d,p) level at 10 K. Second, the geometries and velocities of the atoms were selected from the simulations.…”

Section: Computational Detailsmentioning

confidence: 99%

Water-accelerated π-Stacking Reaction in Benzene Cluster Cation

Iura

Kawabata

2019

Sci Rep

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Single molecule electron devices (SMEDs) have been widely studied through both experiments and theoretical calculations because they exhibit certain specific properties that general macromolecules do not possess. In actual SMED systems, a residual water molecule strongly affects the electronic properties of the SMED, even if only one water molecule is present. However, information about the effect of H2O molecules on the electronic properties of SMEDs is quite limited. In the present study, the effect of H2O on the ON-OFF switching property of benzene-based molecular devices was investigated by means of a direct ab initio molecular dynamics (AIMD) method. T- and H-shaped benzene dimers and trimers were examined as molecular devices. The present calculations showed that a H2O molecule accelerates the π-stacking formation in benzene molecular electronic systems. The times of stacking formation in a benzene dimer cation (n = 2) were calculated to be 460 fs (H2O) and 947 fs (no-H2O), while those in a trimer cation (n = 3) were 551 fs (H2O) and 1019 fs (no-H2O) as an average of the reaction time. This tendency was not dependent on the levels of theory used. Thus, H2O produced positive effects in benzene-based molecular electronics. The mechanism of π-stacking was discussed based on the theoretical results.