Reactive scattering dynamics of rotational wavepackets: A case study using the model H+H2 and F+H2 reactions with aligned and anti-aligned H2

Abstract

We propose a method to steer the outcome of reactive atom-diatom scattering, using rotational wavepackets excited by strong non-resonant laser pulses. Full close-coupled quantum mechanical scattering calculations of the D+H2 and F+H2 reactions are presented, where the H2 molecule exists as a coherent superposition of rotational states. The nuclear spin selective control over the molecular bond axis alignment afforded by the creation of rotational wavepackets is applied to reactive scattering systems, enabling a nuclear spin selective influence to be exerted over the reactive dynamics. The extension of the conventional eigenstate-to-eigenstate scattering problem to the case in which the initial state is composed of a coherent superposition of rotational states is detailed, and a selection of example calculations are discussed, along with their mechanistic implications. The feasibility of the corresponding experiments is considered, and a suitable simple two pulse laser scheme is shown to strongly differentiate the reactivities of o-H2 and p-H2.

Laser Sculpting of Atomic sp, sp2, and sp3 Hybrid Orbitals

“…[38] They also lend themselves to state-selective investigations of elementary processes in heterogeneous catalysis, such as scattering (sticking) of H atoms off (to) surfaces. Analogous revivals of vibrational [48] or rotational wavepackets [44,49] demonstrate that this is long enough for applications, for example, for state-selective sequel processes. [45,46] Relativistic extension of the present approach will allow effects of the fine structure of the excited states to be accounted for.…”

“…After laser hybridization, the orbitals can be monitored experimentally by techniques equivalent to those used for measuring the shapes of laser-sculpted atomic Rydberg wavepackets. [39,40] Moreover, H atoms and four isotopes [41] in sp n hybrid states may be used as state-selective reactants in elementary chemical reactions such as H + F 2 !HF + F. [36,37,[42][43][44] Hybrid-state selectivity may also be extended to femtosecond laser control of photoassociation reactions. For example, they may serve as targets for electron scattering to produce state-selective differential scattering cross sections.…”

“…[39,40] Moreover, H atoms and four isotopes [41] in sp n hybrid states may be used as state-selective reactants in elementary chemical reactions such as H + F 2 !HF + F. [36,37,[42][43][44] Hybrid-state selectivity may also be extended to femtosecond laser control of photoassociation reactions. [38][39][40][41][42][43][44][45][46] Periods of recurrences would decrease for heavier atoms, according to increasing differences of the quantum defects for the nondegenerate excited states, which are characterized by s and p orbitals. The Lamb shift between 2s 1/2 and 2p 1/2 is 1.06 h*GHz, [16,47] where h is the Planck constant, causing periodic dephasings and revivals of the hybrid orbitals, with period 1/1.06 ns.…”

“…[38] They also lend themselves to state-selective investigations of elementary processes in heterogeneous catalysis, such as scattering (sticking) of H atoms off (to) surfaces. [39,40] Moreover, H atoms and four isotopes [41] in sp n hybrid states may be used as state-selective reactants in elementary chemical reactions such as H + F 2 !HF + F. [36,37,[42][43][44] Hybrid-state selectivity may also be extended to femtosecond laser control of photoassociation reactions. [45,46] Relativistic extension of the present approach will allow effects of the fine structure of the excited states to be accounted for.…”

“…Analogous revivals of vibrational [48] or rotational wavepackets [44,49] demonstrate that this is long enough for applications, for example, for state-selective sequel processes. [38][39][40][41][42][43][44][45][46] Periods of recurrences would decrease for heavier atoms, according to increasing differences of the quantum defects for the nondegenerate excited states, which are characterized by s and p orbitals. Hence, H atoms are most suitable for laser sculpting of sp, sp 2 , and sp 3 orbitals, compared with other atoms.…”