Unified treatment of recoil and Doppler broadening in molecular high-energy photoemission

Abstract

Doppler and recoil effects are an integral part of the photoemission process at the high kinetic energies reached in hard x-ray photo-electron spectroscopy (HAXPES) and have a major effect on the observed lineshape, resulting in broadening, energy losses and discrete excitations. These effects can be modeled with a high degree of detail for small systems like diatomic molecules, for larger systems such treatment is often superfluous as the fine spectral features are not observable. We present a united description of the Doppler and recoil effects for arbitrary polyatomic systems and offer an approximate description of the recoil- and Doppler-modified photoemission spectral lineshape as a practical tool in the analysis of HAXPES spectra of core-level photoemission. The approach is tested on the examples of carbon dioxide and pentane molecules. The C and O 1s photoelectron spectra of CO2 in gas phase were also measured at 2.3 and 7.0 keV photon energy at Synchrotron SOLEIL and the spectra were analyzed using the model description. The limitations and applicability of the approach to adsorbates, interfaces and solids is briefly discussed.

Recoil lineshapes in hard X-ray photoelectron spectra of large molecules – free and anchored-on-surface 10-aminodecane-1-thiol

“…Development of synchrotron-based high-resolution electron spectroscopy, especially in the HAXPES regime, has allowed to directly investigate the recoil-induced effects in the molecular core-level photoemission of single gas-phase molecules and to model them at various levels of precision. 14,25,29,30 These and other experimental studies have uniformly confirmed the validity of the fundamental assumptions in the recoil models, which can be summarized as follows:…”

“…Knowing the coefficients f n , the Poisson distributions of recoil-induced vibrational excitations in each vibrational oscillator n at T = 0 K can be obtained. 25 They have the mean (average recoil energy), variance and skewness as…”

“…However, the photoelectron lineshape in the HAXPES regime should receive special scrutiny due to the new contributing factors that could safely be neglected in the near-threshold spectra. Here, we concentrate on two effects that gain prominence in the HAXPES regimethe recoil [12][13][14][15][16][17][18][19][20][21][22][23][24][25] and Doppler 22,23,[25][26][27][28] effects in electron emission, either by direct photoemission or as Auger electrons. energy of the outgoing electron.…”

Simulation of Auger decay dynamics in the hard X-ray regime: HCl as a showcase

“…In near future, we also expect 2D-maps with significantly higher experimental resolution to provide more detailed information, since new high-resolution monochromators in the HAXPES regime are now available, providing a photon energy resolutions of E /Δ E of almost 50.000 at 7 keV. 46 2D-Maps measured with such high experimental resolution will reveal in particular in the resonant Auger region much finer details and will provide a benchmark for theoretical descriptions.…”

Ultrafast dissociation of ammonia: Auger Doppler effect and redistribution of the internal energy

“…5,9 However, in the case of molecular fragments possessing several vibrational degrees of freedom, there are more ways to dissipate the internal energy as well as to excite recoil-induced vibrations and rotations. 20 Dispersion of the E KER with the electron energy, extracted from the experimental data for the NH 2 + –H dissociation channel, shows that about 43% of the internal energy remaining in the system after emission of the resonant Auger electron is transferred to vibrations, while recoil-induced rovibronic excitations are weak owing to the relatively high mass ratio of the co-fragments ( m NH 2 / m H = 16 : 1).…”