Molecular dynamics of methanol cation (CH 3 OH + ) in strong fields: Comparison of 800 nm and 7 μm laser fields

The Journal of Chemical Physics

2016

Self Cite

The hydrogens in protonated acetylene are very mobile and can easily migrate around the C2 core by moving between classical and non-classical structures of the cation. The lowest energy structure is the T-shaped, non-classical cation with a hydrogen bridging the two carbons. Conversion to the classical H2CCH(+) ion requires only 4 kcal/mol. The effect of circularly polarized light on the migration of hydrogens in oriented C2H3 (+) has been simulated by Born-Oppenheimer molecular dynamics. Classical trajectory calculations were carried out with the M062X/6-311+G(3df,2pd) level of theory using linearly and circularly polarized 32 cycle 7 μm cosine squared pulses with peak intensity of 5.6 × 10(13) W/cm(2) and 3.15 × 10(13) W/cm(2), respectively. These linearly and circularly polarized pulses transfer similar amounts of energy and total angular momentum to C2H3 (+). The average angular momentum vectors of the three hydrogens show opposite directions of rotation for right and left circularly polarized light, but no directional preference for linearly polarized light. This difference results in an appreciable amount of angular displacement of the three hydrogens relative to the C2 core for circularly polarized light, but only an insignificant amount for linearly polarized light. Over the course of the simulation with circularly polarized light, this corresponds to a propeller-like motion of the three hydrogens around the C2 core of protonated acetylene.

Section: Resultsmentioning

confidence: 87%

Computational simulations of hydrogen circular migration in protonated acetylene induced by circularly polarized light

Shi

The Journal of Chemical Physics

2016

Self Cite

“…The simulations of dissociation were carried out by classical trajectory calculations on the ground state Born‐Oppenheimer surface for aligned formyl chloride cations in the time varying electric field of the laser pulses. As in our previous studies, the B3LYP/6‐311G(d,p) level of theory was chosen as a suitable compromise between accuracy of the potential energy surface and efficiency in the trajectory calculations. Molecular dynamics calculations were carried out with the development version of the Gaussian series of programs and the PCvelV integrator with a step size of 0.25 fs and Hessian updating for 20 steps before recalculation of the Hessian.…”

Section: Methodsmentioning

confidence: 99%

Controlling the strong field fragmentation of ClCHO⁺ using two laser pulses –an ab initio molecular dynamics simulation

Shi

2018

J Comput Chem

Self Cite

For a single, intense 7 μm linearly polarized laser pulse, we found that the branching ratio for the fragmentation of ClCHO+ → Cl + HCO+, H + ClCO+, HCl++CO depended strongly on the orientation of the molecule (J. Phys. Chem. Lett. 2012, 3 2541). The present study explores the possibility of controlling the branching ratio for fragmentation by using two independent pulses with different frequencies, alignment and delay. Born‐Oppenheimer molecular dynamics simulations in the laser field were carried out with the B3LYP/6‐311G(d,p) level of theory using combinations of 3.5, 7 and 10.5 μm sine squared pulses with field strengths of 0.03 au (peak intensity of 3.15×1013 W/cm2) and lengths of 560 fs. A 3.5 μm pulse aligned with the C‐H bond and a 10.5 μm pulse perpendicular to the C‐H bond produced a larger branching ratio for HCl++CO than a comparable single 7 μm pulse. When the 10.5 μm pulse was delayed by one quarter of the pulse envelope, the branching ratio for the high energy product, (HCl++CO 73%) was a factor of three larger than the low energy product (Cl + HCO+, 25%). By contrast, when the 3.5 μm pulse was delayed by one quarter of the pulse envelope, the branching ratio was reversed (HCl++CO 38%; Cl + HCO+, 60%). Continuous wavelet analysis was used to follow the interaction of the laser with the various vibrational modes as a function of time. © 2018 Wiley Periodicals, Inc.

“…By contrast, mid-IR laser fields interacted directly with the molecular vibrations of CH 3 OH + , depositing enough energy to cause significant amounts of isomerization and dissociation on the ground-state surface. 12 Our simulations of ClCHO + , CF 3 Br + , and C 6 H 5 I 2+ showed that intense mid-IR pulses were able to selectively enhance specific reaction channels for aligned molecules. 1,2 Therefore, in the present paper, we focus on mid-IR laser pulses and consider both randomly oriented and aligned molecules.…”

Section: ■ Introductionmentioning

confidence: 94%

“…In prior work, we used ab initio classical trajectory calculations to investigate the dynamics of the methanol monocation on the ground-state potential energy surface in the presence of a strong laser field. , Classical dynamics simulations showed that ground-state methanol cation gained only a few kcal/mol from an 800 nm laser field, suggesting that excited states and coupled nuclear–electron dynamics may be important for interactions with 800 nm laser pulses. By contrast, mid-IR laser fields interacted directly with the molecular vibrations of CH 3 OH + , depositing enough energy to cause significant amounts of isomerization and dissociation on the ground-state surface . Our simulations of ClCHO + , CF 3 Br + , and C 6 H 5 I 2+ showed that intense mid-IR pulses were able to selectively enhance specific reaction channels for aligned molecules. , Therefore, in the present paper, we focus on mid-IR laser pulses and consider both randomly oriented and aligned molecules.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics of Methylamine, Methanol, and Methyl Fluoride Cations in Intense 7 Micron Laser Fields

Thapa

2014

J. Phys. Chem. A

Self Cite

Fragmentation and isomerization of methylamine (CH3NH2(+)), methanol (CH3OH(+)), and methyl fluoride (CH3F(+)) cations by short, intense laser pulses have been studied by ab initio classical trajectory calculations. Born-Oppenheimer molecular dynamics (BOMD) on the ground-state potential energy surface were calculated with the CAM-B3LYP/6-31G(d,p) level of theory for the cations in a four-cycle laser pulse with a wavelengths of 7 μm and intensities of 0.88 × 10(14) and 1.7 × 10(14) W/cm(2). The most abundant reaction path was CH2X(+) + H (63-100%), with the second most favorable path being HCX(+) + H2 (0-33%), followed by isomerization to CH2XH(+) (0-8%). C-X cleavage after isomerization was observed only in methyl fluoride. Compared to random orientation, CH3X(+) with the C-X aligned with the laser polarization gained energy nearly twice as much from laser fields. The percentage of CH3(+) + X dissociation increased when the C-X bond was aligned with the laser field. Alignment also increased the branching ratio for H2 elimination in CH3NH2(+) and CH3OH(+) and for isomerization in CH3OH(+).