Intense 2-cycle laser pulses induce time-dependent bond-hardening in a polyatomic molecule

TL;DR

This study demonstrates that intense few-cycle laser pulses can induce a time-dependent bond-hardening effect in a polyatomic molecule, enabling the optical generation and control of ions typically inaccessible in mass spectrometry.

Contribution

The paper reveals a novel time-dependent bond-hardening process in a polyatomic molecule using strong, few-cycle laser pulses, allowing control over molecular ion stability.

Findings

Field-induced potential well traps molecular wavepackets.

Longer pulses allow wavepacket leakage, reversing bond-hardening.

Optical control enables generation of otherwise inaccessible ions.

Abstract

A time-dependent bond-hardening process is discovered in a polyatomic molecule (tetramethyl silane, TMS) using few-cycle pulses of intense 800 nm light. In conventional mass spectrometry, symmetrical molecules like TMS do not exhibit a prominent molecular ion (TMS$^+$) as unimolecular dissociation into [Si(CH$_3$)$_3]^+$ proceeds very fast. Under strong field and few-cycle conditions, this dissociation channel is defeated by time-dependent bond-hardening: a field-induced potential well is created in the TMS$^+$ potential energy curve that effectively traps a wavepacket. The time-dependence of this bond hardening process is verified using longer-duration ($\geq$ 100 fs) pulses; the relatively "slower" fall-off of optical field in such pulses allows the initially trapped wavepacket to leak out, thereby rendering TMS$^+$ unstable once again. Our results are significant as they demonstrate (i) optical generation of polyatomic ions that are normally inaccessible and (ii) optical control of dynamics in strong fields, with distinct advantages over weak-field control scenarios that demand a narrow bandwidth appropriate for a specified transition.