Pendular alignment and strong chemical binding are induced in helium dimer molecules by intense laser fields

Abstract

Intense pulsed-laser fields have provided means to both induce spatial alignment of molecules and enhance strength of chemical bonds. The duration of the laser field typically ranges from hundreds of picoseconds to a few femtoseconds. Accordingly, the induced "laser-dressed" properties can be adiabatic, existing only during the pulse, or nonadiabatic, persisting into the subsequent field-free domain. We exemplify these aspects by treating the helium dimer, in its ground [Formula: see text] and first excited [Formula: see text] electronic states. The ground-state dimer when field-free is barely bound, so very responsive to electric fields. We examine two laser realms, designated (I) "intrusive" and (II) "impelling." I employs intense nonresonant laser fields, not strong enough to dislodge electrons, yet interact with the dimer polarizability to induce binding and pendular states in which the dimer axis librates about the electric field direction. II employs superintense high-frequency fields that impel the electrons to undergo quiver oscillations, which interact with the intrinsic Coulomb forces to form an effective binding potential. The dimer bond then becomes much stronger. For I, we map laser-induced pendular alignment within the X state, which is absent for the field-free dimer. For II, we evaluate vibronic transitions from the X to A states, governed by the amplitude of the quiver oscillations.

Electric-field-induced helium-helium resonances

“…[9] for the 3 He- 4 He and 3 He- 3 He systems and for the 4 He- 4 He system in Ref. [13], can be observed experimentally in time-dependent set-ups. To interpret the dynamic wave packet studies, the static field case is revisited and some quantitative discrepancies with the literature [9], which we have no explanation for, are pointed out.…”

“…and larger than about 0,S = 0.0976a.u.. No evidence for the existence of these states is reported in Ref. [13]. For field strengths larger than about 0,S = 0.10962a.u., a new bound state with appreciable d-wave admixture is being supported [also notice the related avoided crossing between the s-wave dominated and d-wave dominated states at ( 0,S , E bind ) ≈ (0.11a.u., 5 × 10 −7 a.u.)].…”

“…The tunability of the 4 He- 4 He system by a static electric field and by laser pulses strong enough to involve electronically excited potential curves was very recently pointed out in Ref. [13].…”

“…Owing to the orbital angular momentum barrier, this bound state acquires an appreciable binding energy over a fairly small variation of the field strength 0,S . Reference [13] refers to this d-wave dominated state as a "pendular state". The 3 He- 4 He system [see Fig.…”

Hovering States of Ammonia in a High-Intensity, High-Frequency Oscillating Field: Trapped into Planarity by Laser-Induced Hybridization

“…Metastable, slowly ionizing, quasi-bound states in the presence of strong high-frequency electromagnetic radiation have been theoretically predicted and experimentally realized since the advent of strong field chemistry and physics . Among these, in the high-frequency regime, there have been stable states of atoms and anions, where the electron overcomes the binding potential and follows the oscillating field in a to and fro motion between the classical turning points of the laser. − This results in dichotomous states of the electron in an atom, where the electron density of the atom now resembles that of a diatomic molecule. − The initial predictions came out of a theoretical construct in which the intensity and frequency of the laser were asymptotically high. , Later, this counterintuitive concept turned into a reality, with an experimental realization of these exotic states in the case of noble gas atoms such as neon, helium, and argon. − Such states have been proposed to be responsible for strong binding effects in the case of diatomic molecules. − …”