| 1. |
- Michiels, R., et al.
(författare)
-
Enhancement of above Threshold Ionization in Resonantly Excited Helium Nanodroplets
- 2021
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 127
-
Tidskriftsartikel (refereegranskat)abstract
- Clusters and nanodroplets hold the promise of enhancing high-order nonlinear optical effects due to their high local density. However, only moderate enhancement has been demonstrated to date. Here, we report the observation of energetic electrons generated by above-threshold ionization (ATI) of helium (He) nanodroplets which are resonantly excited by ultrashort extreme ultraviolet (XUV) free-electron laser pulses and subsequently ionized by near-infrared (NIR) or near-ultraviolet (UV) pulses. The electron emission due to high-order ATI is enhanced by several orders of magnitude compared with He atoms. The crucial dependence of the ATI intensities with the number of excitations in the droplets suggests a local collective enhancement effect.
|
|
| 2. |
|
|
| 3. |
- Abu-samha, M, et al.
(författare)
-
The local structure of small water clusters : imprints on the core-level photoelectron spectrum
- 2009
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 42:5, s. 055201-
-
Tidskriftsartikel (refereegranskat)abstract
- We report on an O 1s photoelectron-spectroscopy study of small neutral water clusters produced by adiabatic expansion. The photoelectron spectra were acquired under two different experimental conditions. At intermediate resolution, the cluster signal was characterized by a very broad O 1s peak with a flat top. In the second set of measurements, resolution was significantly increased at the cost of lower count rates. The cluster signal was now partly resolved into a bimodal structure. Extensive theoretical calculations were undertaken to facilitate an interpretation of the spectrum. These results suggest that the bimodal feature may be ascribed to ionization of water molecules in different hydrogen-bonding configurations, more specifically, molecules characterized by donation of either one or both hydrogen atoms in H-bonding.
|
|
| 4. |
|
|
| 5. |
- Harnes, J., et al.
(författare)
-
The structure of mixed methanol/chloroform clusters from core-level photoelectron spectroscopy and modeling
- 2011
-
Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1144-0546 .- 1369-9261. ; 35:11, s. 2564-2572
-
Tidskriftsartikel (refereegranskat)abstract
- Mixed neutral molecular clusters have been produced by co-expansion of chloroform and methanol and characterized by carbon 1s photoelectron spectroscopy and theoretical modeling. The produced clusters are in the range 50-150 molecules and the clusters are not homogeneously mixed: chloroform is enriched in the bulk and methanol is found on or close to the surface. This is based on evidence from photoelectron depth profiling and molecular dynamics simulations of mixed clusters. The simulations suggest that methanol forms cyclic or linear oligomers in the surface layers of the mixed clusters. From thermodynamic models, the enrichment of methanol on the cluster surface can be rationalized from the difference in surface tension between the two pure components, which is connected to the qualitative differences in the respective bonding patterns.
|
|
| 6. |
- Abu-samha, M, et al.
(författare)
-
Lineshapes in carbon 1s photoelectron spectra of methanol clusters
- 2006
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 8:21, s. 2473-2482
-
Tidskriftsartikel (refereegranskat)abstract
- A general protocol for theoretical modeling of inner-shell photoelectron spectra of molecular clusters is presented and applied to C1s spectra of oligomers and medium-sized clusters of methanol. The protocol employs molecular dynamics for obtaining cluster geometries and a polarizable force field for computing site-specific chemical shifts in ionization energy and linewidth. Comparisons to spectra computed from first-principle theories are used to establish the accuracy of the proposed force field approach. The model is used to analyze the C1s photoelectron spectrum of medium-sized clusters in terms of surface and bulk contributions. By treating the surface-to-bulk ratio as an adjustable parameter, satisfactory fits are obtained to experimental C1s spectra of a beam of methanol clusters.
|
|
| 7. |
- Abu-samha, M., et al.
(författare)
-
What Can C1s Photoelectron Spectroscopy Tell about Structure and Bonding in Clusters of Methanol and Methyl Chloride?
- 2007
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 111:37, s. 8903-8909
-
Tidskriftsartikel (refereegranskat)abstract
- Single-component clusters of methanol and methyl chloride have been produced by adiabatic expansion, and their carbon Is photoelectron spectra were recorded using synchrotron radiation and a high-resolution electron analyzer. The experimental spectra are interpreted by means of theoretical models based on molecular dynamics simulations. The data are used to explore to what extent core-level photoelectron spectra may provide information on the bonding mechanism and the geometric structure of clusters of polar molecules. The results indicate that the cluster-to-monomer shift in ionization energy and also the width of the cluster peak may be used to distinguish between hydrogen bonding and weaker electrostatic interactions. Moreover, the larger width of the cluster peak in methanol clusters as compared to methyl chloride clusters is partly due to the structured surface of methanol clusters. Theoretical modeling greatly facilitates the analysis of core-level photoelectron spectra of molecular clusters.
|
|
| 8. |
- Bergersen, Henrik, et al.
(författare)
-
First observation of vibrations in core-level photoelectron spectra of free neutral molecular clusters
- 2006
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 429:1-3, s. 109-113
-
Tidskriftsartikel (refereegranskat)abstract
- Core-level photoelectron spectra of free neutral methane clusters have been recorded. These spectra exhibit well-resolved surface and bulk features as well as vibrational fine structure. The vibrational structure in the cluster signal is well reproduced by a theoretical model that assumes independent contributions from inter- and intramolecular modes. The intramolecular contribution to the vibrational line-shape is taken to be equal to that of the monomer in the gas phase, while the intermolecular part is simplified to line broadening. An estimate of the cluster size has been made on the basis of the observed surface-to-bulk intensity ratio.
|
|
| 9. |
|
|
| 10. |
- Bergersen, Henrik, et al.
(författare)
-
Two size regimes of methanol clusters produced by adiabatic expansion
- 2006
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:18, s. 184303-
-
Tidskriftsartikel (refereegranskat)abstract
- Free neutral methanol clusters produced by adiabatic expansion have been studied by photoelectron spectroscopy and line shape modeling. The results show that clusters belonging to two distinct size regimes can be produced by changing the expansion conditions. While the larger size regime can be well described by line shapes calculated for clusters consisting of hundreds of molecules, the smaller size regime corresponds to methanol oligomers, predominantly of cyclic structure. There is little contribution from dimers to the spectra.
|
|
