Direct inner-shell photoionization of Xe atoms embedded in helium nanodroplets

Abstract

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 ions due to electron transfer to the primary Auger ions from surrounding neutral atoms. The electron spectra correlated with Xe ions emitted from the He nanodroplets contain a low-energy feature and nearly unshifted Xe photolines. These results pave the way to extreme ultraviolet (XUV) and x-ray photoelectron spectroscopy of clusters and molecular complexes embedded in He nanodroplets.

Electron and ion spectroscopy of camphor doped helium nanodroplets in the extreme UV and soft x-ray regime

“…Similar observations are recently reported for nucleobases in He nanodroplets [53]. As ICD predominantly produces unfragmented parent ions, the latter could be used as a messenger for measuring the excitation spectrum of helium nanodroplets, as in previous studies used atomic [46,72] and molecular dopants [48]. Additionally, ion mass spectrum contains peaks corresponding to the camphor dimer (m/q = 304) and trimer (m/q = 456) cations, with smaller abundance than camphor monomer ion.…”

Secondary ionization of pyrimidine nucleobases and their microhydrated derivatives in helium nanodroplets

“…In fact, previous attempts to detect dopants’ photoelectrons and ions by directly photoionizing dopants in HNDs have remained unsuccessful except for a few particularly favorable cases. 32,33…”

“…In fact, previous attempts to detect dopants' photoelectrons and ions by directly photoionizing dopants in HNDs have remained unsuccessful except for a few particularly favorable cases. 32,33 The various fragmentation channels of Cyt [34][35][36] and Thy 37-39 have been identified by means of high-resolution mass spectrometry and quantum chemical calculations. From photoionization of effusive Cyt and Thy, we identify two main fragments in agreement with mass spectra reported in the literature.…”

Doubly charged dimers and trimers of heavy noble gases

“…However, photoelectron experiments of HNDs doped with noble gas atoms (which are heliophilic) have shown that Penning ionization does occur in small HNDs if the incident radiation leads to excitation of the 1s2p or higher bands. [55][56][57] A better understanding of the ionization mechanism could be obtained if the ion yield were to be measured versus the energy of the incident electrons, but this kind of experiment would require higher ion yields than attainable right now.…”