Elucidating the origins of multimode vibrational coherences of polyatomic molecules induced by intense laser fields

Zhengrong Wei,Soo Teck See,Fan Shi,Yingfeng Zhang,Zhi-Heng Loh,Minghui Yang,Lin Wang,Jialin Li,Mark Hyunpong Jhon

doi:10.1038/s41467-017-00848-2

Abstract

Strong-field laser–molecule interaction forms much of the basis for initiating and probing ultrafast quantum dynamics. Previous studies aimed at elucidating the origins of vibrational coherences induced by intense laser fields have been confined to diatomic molecules. Furthermore, in all cases examined to date, vibrational wave packet motion is found to be induced by R-selective depletion; wave packet motion launched by bond softening, though theoretically predicted, remains hitherto unobserved. Here we employ the exquisite sensitivity of femtosecond extreme ultraviolet absorption spectroscopy to sub-picometer structural changes to observe both bond softening-induced vibrational wave packets, launched by the interaction of intense laser pulses with iodomethane, as well as multimode vibrational motion of the parent ion produced by strong-field ionization. In addition, we show that signatures of coherent vibrational motion in the time-dependent extreme ultraviolet absorption spectra directly furnish vibronic coupling strengths involving core-level transitions, from which geometrical parameters of transient core-excited states are extracted.

Highlights

Strong-field laser–molecule interaction forms much of the basis for initiating and probing ultrafast quantum dynamics
Femtosecond intense laser–matter interaction[1] has emerged as a powerful approach for unraveling the ultrafast quantum dynamics of molecules via processes such as high-order harmonic generation[2], above-threshold ionization[3], and laserinduced electron diffraction[4]. These phenomena have in turn been applied to, for example, the tomographic imaging of molecular orbitals[5, 6], the investigation of attosecond electronic wave packet dynamics[7,8,9], and the retrieval of transient molecular structures[10,11,12]. While many of these studies aim to elucidate electronic dynamics, it is important to realize that the intense laser–molecule interaction inevitably triggers coherent vibrational motion, whose coupling to the electronic degrees of freedom will invariably affect the outcome and interpretation of experiments and theories that nominally seek to address electron dynamics[13,14,15]
Other factors that motivate the investigation of coherent vibrational dynamics in the strong-field regime include the prospect of employing intense laser fields to manipulate molecular dynamics[16,17,18,19] and the identification of ion electronic states produced by strong-field ionization by measuring their vibrational quantum beat frequencies[20]

Summary

Introduction

Strong-field laser–molecule interaction forms much of the basis for initiating and probing ultrafast quantum dynamics. We employ the exquisite sensitivity of femtosecond extreme ultraviolet absorption spectroscopy to sub-picometer structural changes to observe both bond softening-induced vibrational wave packets, launched by the interaction of intense laser pulses with iodomethane, as well as multimode vibrational motion of the parent ion produced by strong-field ionization. Femtosecond intense laser–matter interaction[1] has emerged as a powerful approach for unraveling the ultrafast quantum dynamics of molecules via processes such as high-order harmonic generation[2], above-threshold ionization[3], and laserinduced electron diffraction[4] These phenomena have in turn been applied to, for example, the tomographic imaging of molecular orbitals[5, 6], the investigation of attosecond electronic wave packet dynamics[7,8,9], and the retrieval of transient molecular structures[10,11,12]. We show that XUV absorption probing of coherent vibrational dynamics allows the retrieval of structural parameters for transient core-excited states

Methods

Results

Conclusion