The desorption of excited rubidium (Rb) atoms off the surface of helium (He) nanodroplets is studied in detail using femtosecond time-resolved photoion and photoelectron imaging spectroscopy in combination with quantum wave packet simulations. The good agreement of the measured time-dependent velocity distributions with the simulation when exciting the Rb dopant atoms into the 6p-state supports the pseudo-diatomic model (PDM) for the Rb-He droplet interaction, even on the level of quantum wave packet dynamics. Time-resolved photoelectron spectra reveal the partitioning of excitation energy into the dopant and the droplet degrees of freedom.
We present the first measurements of photoelectron spectra of atomic clusters embedded in superfluid helium (He) nanodroplets. Owing to the large absorption cross section of xenon (Xe) around 100 eV photon energy (4d inner-shell ionization), direct dopant photoionization exceeds charge transfer ionization via the ionized He droplets. Despite the predominant creation of Xe^2+ and Xe^3+ by subsequent Auger decay of free Xe atoms, for Xe embedded in He droplets only singly charged Xe_k^+, k=1,2,3 fragments are observed. Broad Xe^+ ion kinetic-energy distributions indicate Coulomb explosion of the…
We present an experimental study of the dynamics following the photo-excitation and subsequent photo-ionization of single Cs atoms on the surface of helium nanodroplets. The dynamics of excited-Cs-atom desorption and re-adsorption as well as CsHe exciplex formation are measured using femtosecond pump-probe velocity-map-imaging spectroscopy and ion-time-of-flight spectrometry. The timescales for the desorption of excited Cs atoms off helium nanodroplets as well as the timescales for CsHe exciplex formation are experimentally determined for the 6p states of Cs. For the 6p $^2Π_ {1/2}$ state, our…
Magnesium atoms fully embedded in helium nanodroplets are exposed to two-color laser pulses, which trigger multiphoton above-threshold ionization (ATI). This allows to exemplarily study the contribution of a dense, neutral and finite medium on single electron propagation. The angular-resolved photoelectron spectra show striking differences with respect to results obtained on free atoms. Scattering of the individual Mg photoelectrons, when traversing the neutral helium environment, causes the angular distribution to become almost isotropic. Furthermore, the appearance of higher energy electrons…
Besides the use as cold matrix for spectroscopic studies, superfluid helium droplets have served as a cold environment for the synthesis of molecules and clusters. Since vibrational frequencies of molecules in helium droplets exhibit almost no shift compared to the free molecule values, one could assume the solvated particles move frictionless and undergo a reaction as soon as their paths cross. There have been a few unexplained observations that seemed to indicate cases of two species on one droplet not forming bonds but remaining isolated. In this work, we performed a systematic study of hel…
Multiple photoelectron inelastic scattering in large He nanodroplets
Aarhus University（奥胡斯大学）；University of Kassel（卡塞尔大学）；Mahindra University Hyderabad（海德拉巴马欣德拉大学）；Sorbonne Université（索邦大学）；Indian Institute of Technology Madras（马德拉斯印度理工学院）；Synchrotron SOLEIL（SOLEIL同步辐射中心）
The relaxation dynamics of superexcited superfluid He nanodroplets is thoroughly investigated by means of extreme-ultraviolet (XUV) femtosecond electron and ion spectroscopy complemented by time-dependent density functional theory (TDDFT). Three main paths leading to the emission of electrons and ions are identified: Droplet autoionization, pump-probe photoionization, and autoionization induced by re-excitation of droplets relaxing into levels below the droplet ionization threshold. The most abundant product of both droplet autoionization and photoionization is He$_2^+$, whereas the delayed ap…
X-ray photoelectron spectroscopy of Ar and Kr clusters formed in He nanodroplets
University of Kassel（卡塞尔大学）；Aarhus University（奥胡斯大学）；Mahindra University Hyderabad（海德拉巴马欣德拉大学）；Sorbonne Université（索邦大学）；Indian Institute of Technology Madras（金奈印度理工学院）；Synchrotron SOLEIL（SOLEIL同步辐射中心）；Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel（卡塞尔大学跨学科纳米结构科学与技术中心）
Complexes of gold and imidazole formed in helium nanodroplets
我们研究了金原子和咪唑（C $_3$ N $_2$ H $_4$，缩写为Im）在氦纳米液滴中生成的配合物。在掺杂液滴的电离之后，我们检测到宽范围的不同Au $_m$ Im $_n^+$络合物，然而，我们发现对于特定值的$m$，某些$n$是“神奇的”，因此特别丰富。我们的密度泛函理论计算表明，这些丰富的簇大小的结果，部分特别稳定的配合物，如AuIm $_2^+$，部分是由于在碎片模式的过渡，从中性咪唑分子的损失为大系统的中性金原子的损失为较小的系统。
When weakly-bound complexes are multiply excited by intense electromagnetic radiation, energy can be exchanged between neighboring atoms through a type of resonant interatomic Coulombic decay (ICD). This decay mechanism due to multiple excitations has been predicted to be relatively slow, typically lasting tens to hundreds of picoseconds. Here, we directly measure the ICD timescale in resonantly excited helium droplets using a high resolution, tunable, extreme ultraviolet free electron laser. Over an extensive range of droplet sizes and laser intensities, we discover the decay to be surprising…
Rubidium dimers residing on the surface of He nanodroplets are doubly ionized by an intense fs laser pulse leading to fragmentation into a pair of $\mathrm{Rb^+}$ ions. We show that the kinetic energy of the $\mathrm{Rb^+}$ fragment ions can be used to identify dimers formed in either the X $^1Σ_{\mathrm{g}}^+$ ground state or in the lowest-lying triplet state, a $^3Σ_{\mathrm{u}}^+$. From the experiment, we estimate the abundance ratio of dimers in the a and X states as a function of the mean droplet size and find values between 4:1 and 5:1. Our technique applies generally to dimers and trime…
We have explored the light induced dynamics in superfluid helium nanodroplets with wide-angle scattering in a pump-probe measurement scheme. The droplets are doped with xenon atoms to facilitate the ignition of a nanoplasma through irradiation with near-infrared laser pulses. After a variable time delay of up to 800 ps, we image the subsequent dynamics using intense extreme ultraviolet pulses from the FERMI free-electron laser. The recorded scattering images exhibit complex intensity fluctuations that are categorized based on their characteristic features. Systematic simulations of wide-angle …
