Mechanisms and time-resolved dynamics for trihydrogen cation (H3 +) formation from organic molecules in strong laser fields

Abstract

Strong-field laser-matter interactions often lead to exotic chemical reactions. Trihydrogen cation formation from organic molecules is one such case that requires multiple bonds to break and form. We present evidence for the existence of two different reaction pathways for H3 + formation from organic molecules irradiated by a strong-field laser. Assignment of the two pathways was accomplished through analysis of femtosecond time-resolved strong-field ionization and photoion-photoion coincidence measurements carried out on methanol isotopomers, ethylene glycol, and acetone. Ab initio molecular dynamics simulations suggest the formation occurs via two steps: the initial formation of a neutral hydrogen molecule, followed by the abstraction of a proton from the remaining CHOH2+ fragment by the roaming H2 molecule. This reaction has similarities to the H2 + H2 + mechanism leading to formation of H3 + in the universe. These exotic chemical reaction mechanisms, involving roaming H2 molecules, are found to occur in the ~100 fs timescale. Roaming molecule reactions may help to explain unlikely chemical processes, involving dissociation and formation of multiple chemical bonds, occurring under strong laser fields.

Time-resolving the ultrafast H2 roaming chemistry and H3+ formation using extreme-ultraviolet pulses

“…excitation of the methanol dication. Over 1/3 of the ground-state trajectories produce H þ 3 , this compared with~4% obtained in previous ground-state simulations that did not include the second order perturbation theory corrections 26 . The high H þ 3 formation probability on the ground state, drops for the higher lying states and is completely quenched once the CO bond cleavage becomes possible above the third excited state.…”

“…However, to understand the ultrafast lifetime of the roaming H 2 it is important to consider also its other decay channels. Earlier AIMD simulations using CISD and CASSCF electronic potentials reported unbalanced charge dissociation of the methanol dication ground state to form H 2 þ CHOH 2þ , with over 11% and 18% branching ratio respectively 18,26 . In contrast, the non-adiabatic AIMD simulations using CASPT2 potentials indicate that the neutral H 2 cannot escape, it is polarized and bound by the CHOH 2þ dication.…”

Quantum coherent control of H3+ formation in strong fields

“…The formation of H 3 + requires double ionization, formation of neutral H 2 , and the abstraction of a proton following roaming. 17 The first and second ionization energies for methanol require the absorption of 7 and 20 (∼1.55 eV) photons, respectively, based on our calculations, under the experimental conditions (Fig. 2).…”

“…[14][15][16] The production of H 3 + proceeds via a mechanism that stems from the formation of a neutral H 2 molecule, which subsequently roams and extracts a proton. 17 The complex mechanism for this reaction requiring the dissociation of three bonds and the creation of three new ones represents an interesting challenge for QCC. Details about the mechanism together with ab initio molecular dynamics simulations for the production of H 3 + from methanol, longer-chain alcohols, and thiols are discussed elsewhere.…”

“…Details about the mechanism together with ab initio molecular dynamics simulations for the production of H 3 + from methanol, longer-chain alcohols, and thiols are discussed elsewhere. [17][18][19]…”