Attosecond spectroscopy of size-resolved water clusters

Abstract

Electron dynamics in water are of fundamental importance for a broad range of phenomena [1-3], but their real-time study faces numerous conceptual and methodological challenges [4][5][6]. Here, we introduce attosecond size-resolved cluster spectroscopy and build up a molecular-level understanding of the attosecond electron dynamics in water. We measure the effect that the addition of single water molecules has on the photoionization time delays [7][8][9][10][11] of water clusters. We find a continuous increase of the delay for clusters containing up to 4-5 molecules and little change towards larger clusters. We show that these delays are proportional to the spatial extension of the created electron hole, which first increases with cluster size and then partially localizes through the onset of structural disorder that is characteristic of large clusters and bulk liquid water. These results establish a previously unknown sensitivity of photoionization delays to electron-hole delocalization and reveal a direct link between electronic structure and attosecond photoemission dynamics. Our results offer novel perspectives for studying electron/hole delocalization and its attosecond dynamics.Electronic dynamics in water play a central role in a broad range of scientific and technological research areas ranging from radiation chemistry to photocatalysis. The dynamics induced by ionization of water are of particular relevance since they initiate the processes underlying radiation damage [2,3,12]. The ionization of water is predicted to lead to the formation of a delocalized electron hole, followed by its localization on one water molecule and proton transfer to a neighboring molecule, forming H 3 O + and OH [13]. The latter step has been time-resolved only very recently using one-photon extreme-ultraviolet (XUV) photoionization of water clusters [4] 1

Symmetry resolved atomic photoionization phase shift by attosecond coincidence metrology

“…Attosecond coincidence interferometer The attosecond photoelectron spectra are measured via an attosecond coincidence interferometer 19,22 . A multipass amplified Titanium-Sapphire laser system which produces a near-infrared (NIR) femtosecond laser pulse with a central wavelength of 790 nm, 1.4 mJ at 10 kHz repetition rate and a pulse duration of 28 fs (full-width at half-maximum in intensity), is used to construct our attosecond optical interferometer through a nonlinear Mach-Zehnder interferometer.…”

“…The XUV-APT and NIR laser fields are phase-locked in the time domain and their relative time delay is manipulated via a delay stage with an attosecond time resolution. To achieve an attosecond stability, the nonlinear interferometer is actively stabilized 17,19,22,42 with a time-jitter around 30 as.…”

“…Both techniques have been applied to a wide range of attosecond time-resolved photoelectron emission dynamics in atoms [6][7][8] , molecules [9][10][11] and even condensed matters [12][13][14][15] . Studies have demonstrated the photoelectron emission time delays arising from different ionization shells [16][17][18] , shape resonances 9,10,19 , electron correlation 20 , orbital asymmetry 21 , spatial asymmetry (chirality) 11 , and electron delocalization 22 . These time delays are attributed to the energy dependence of the scattering phase shift during electron transitions in a short-range potential and the laser field coupling effect in the continuum 23,24 .…”

A multiple scattering theoretical approach to time delay in high energy core-level photoemission of heteronuclear diatomic molecules

“…Recent developments of attosecond light sources using high-harmonic generation (HHG) combined with the advanced attosecond metrology such as attosecond streaking [1,2,3] and reconstruction of attosecond beating by interference of two-photon transitions [4,5] have enabled us to measure attosecond photoemission time delay in atoms [2,6,7], molecules [8,9,10,11,12,13,14], clusters [15], solids [1,16,17,18], and liquid [19], in the range of extreme ultraviolet wavelengths. The wavelengths of the attosecond HHG light sources have been becoming shorter and shorter and reached the water window region [20,21,22].…”