Disentangling the role of laser coupling in directional breaking of molecules

TL;DR

This paper introduces a new technique to distinguish the effects of laser-induced electronic state coupling from selective ionization in the directional dissociation of molecules, specifically CO+, using tailored laser pulses and photoelectron measurements.

Contribution

The study provides a novel experimental approach to unambiguously identify the roles of laser-induced state coupling versus selective ionization in molecular dissociation processes.

Findings

Laser-induced electronic state coupling significantly influences directional bond breaking.

The technique successfully differentiates ionization and dissociation pathways.

Quantum calculations support the experimental observations.

Abstract

The directional control of molecular dissociation with the laser electric field waveform is a paradigm and was demonstrated for a variety of molecules. In most cases, the directional control occurs via a dissociative ionization pathway. The role of laser-induced coupling of electronic states in the dissociating ion versus selective ionization of oriented neutral molecules, however, could not be distinguished for even small heteronuclear molecules such as CO. Here, we introduce a technique, using elliptically polarized pump and linearly polarized two-color probe pulses that unambiguously distinguishes the roles of laser-induced state coupling and selective ionization. The measured photoelectron momentum distributions governed by the light polarizations allow us to coincidently identify the ionization and dissociation from the pump and probe pulses. Directional dissociation of CO+ as a function of the relative phase of the linearly polarized two-color pulse is observed for both parallel and orthogonally oriented molecules. We find that the laser-induced coupling of various electronic states of CO+ plays an important role for the observed directional bond breaking, which is verified by quantum calculations.