Phase- and intensity-dependence of ultrafast dynamics in hydrocarbon molecules in few-cycle laser fields

M Kübel,C Burger,R Siemering,Nora G Kling,B Bergues,A S Alnaser,I Ben-Itzhak,R Moshammer,R De Vivie-Riedle,M F Kling

doi:10.1080/00268976.2017.1288935

Abstract

ABSTRACTIn strong laser fields, sub-femtosecond control of chemical reactions with the carrier-envelope phase (CEP) becomes feasible. We have studied the control of reaction dynamics of acetylene and allene in intense few-cycle laser pulses at 750 nm, where ionic fragments are recorded with a reaction microscope. We find that by varying the CEP and intensity of the laser pulses, it is possible to steer the motion of protons in the molecular dications, enabling control over deprotonation and isomerisation reactions. The experimental results are compared to predictions from a quantum dynamical model, where the control is based on the manipulation of the phases of a vibrational wave packet by the laser waveform. The measured intensity-dependence in the CEP-controlled deprotonation of acetylene is well captured by the model. In the case of the isomerisation of acetylene, however, we find differences in the intensity-dependence between experiment and theory. For the isomerisation of allene, an inversion of the CEP-dependent asymmetry is observed when the intensity is varied, which we discuss in light of the quantum dynamical model. The inversion of the asymmetry is found to be consistent with a transition from non-sequential to sequential double ionisation.

Highlights

In the past few decades, strong-field lasers have proven to be valuable tools for the manipulation of chemical bonds
Experimental results are discussed within the framework of a quantum dynamical model, where the CEPdependence of photochemical reactions arises from the preparation and manipulation of a multimode vibrational wavepacket
We have studied the combined carrier-envelope phase (CEP)- and intensitydependence of ionisation and fragmentation processes in the small hydrocarbons acetylene and allene

Summary

Introduction

In the past few decades, strong-field lasers have proven to be valuable tools for the manipulation of chemical bonds. In order to achieve and observe such phenomena, experimental and theoretical efforts, in particular on small molecules, have been extensive Understanding dynamic systems on a small scale is a prerequisite for moving towards more complex molecules and reactions, and their control. Molecular processes and chemical reactions are governed by nuclear motion and the motion of the valence electrons. Control of the reaction to give desired products is achieved through the manipulation of both nuclear and electronic motions, on their respective time scales. It depends on the molecular system, whether it is the nuclear or electron dynamics, or both, that offer the most

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Conclusion