Ultraviolet Photoemission Spectroscopy of Solid Nitrogen and Oxygen

Himpsel, F. J.; Schwentner, N.; Koch, E. E.

doi:10.1002/pssb.2220710223

Cited by 64 publications

(19 citation statements)

References 23 publications

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“…We observe a minimum around 10.5 eV that coincides with the ionization threshold of molecular oxygen in the condensed phase (Himpsel et al 1975). This would mean that ionic species are involved in the desorption mechanism.…”

Section: Oxygen Photodesorptionmentioning

confidence: 58%

Wavelength-dependent UV photodesorption of pure N₂and O₂ices

Fayolle

Bertin

Romanzin

et al. 2013

A&A

125

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Context. Ultraviolet photodesorption of molecules from icy interstellar grains can explain observations of cold gas in regions where thermal desorption is negligible. This non-thermal desorption mechanism should be especially important where UV fluxes are high. Aims. N 2 and O 2 are expected to play key roles in astrochemical reaction networks, both in the solid state and in the gas phase. Measurements of the wavelength-dependent photodesorption rates of these two infrared-inactive molecules provide astronomical and physical-chemical insights into the conditions required for their photodesorption. Methods. Tunable radiation from the DESIRS beamline at the SOLEIL synchrotron in the astrophysically relevant 7 to 13.6 eV range is used to irradiate pure N 2 and O 2 thin ice films. Photodesorption of molecules is monitored through quadrupole mass spectrometry. Absolute rates are calculated by using the well-calibrated CO photodesorption rates. Strategic N 2 and O 2 isotopolog mixtures are used to investigate the importance of dissociation upon irradiation. Results. N 2 photodesorption mainly occurs through excitation of the b 1 Π u state and subsequent desorption of surface molecules. The observed vibronic structure in the N 2 photodesorption spectrum, together with the absence of N 3 formation, supports that the photodesorption mechanism of N 2 is similar to CO, i.e., an indirect DIET (Desorption Induced by Electronic Transition) process without dissociation of the desorbing molecule. In contrast, O 2 photodesorption in the 7−13.6 eV range occurs through dissociation and presents no vibrational structure. Conclusions. Photodesorption rates of N 2 and O 2 integrated over the far-UV field from various star-forming environments are lower than for CO. Rates vary between 10 −3 and 10 −2 photodesorbed molecules per incoming photon.

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Section: Oxygen Photodesorptionmentioning

confidence: 58%

Wavelength-dependent UV photodesorption of pure N₂and O₂ices

Fayolle

Bertin

Romanzin

et al. 2013

A&A

125

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“…The gas-phase resonances lying in the 17-19-eV energy range belong to Rydberg series converging to the b 4 Z g~ state of O2 of which the adiabatic energy is 18.17 eV [8,9,[13][14][15]. The b %" adiabatic ionization energy in solid O2 is 16.5 eV [16]. The strong gas-to-solid redshift (1.7 eV) of this ionization energy leads to an interesting effect.…”

Section: Photon-stimulated Charge Transfer In Condensed 0 2 Studied Bmentioning

confidence: 99%

“…It is known indeed from photoemission spectroscopy of solid oxygen [16] that the kinetic-energy distribution of photoelectrons issued from reaction (1) is dominated by the ionization from the \Yl u orbital of O2. This gives an effective threshold energy of the kinetic-energy distribution at about hv-15 eV although there exists an ionization potential energy of solid O2 lower than 15 eV.…”

Section: Photon-stimulated Charge Transfer In Condensed 0 2 Studied Bmentioning

confidence: 99%

“…The resonant processes are of particular interest since they give evidence of highly excited states which could not be observed by other methods. Such resonant states lying between 6 and 12 eV above the lowest ionization energy of condensed O2 [16] are believed to be derived from O2 superexcited Rydberg states which are known in isolated gas-phase molecules, however, with different lifetimes and energies. The photoelectron-induced processes also reveal important features of the photon-stimulated reactions in condensed molecules.…”

Section: Photon-stimulated Charge Transfer In Condensed 0 2 Studied Bmentioning

confidence: 99%

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Photon-stimulated charge transfer in condensedO2studied by negative-ion desorption

et al. 1991

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Photon-stimulated desorption of negatively charged ions from condensed O2 is observed in the 17-42-eV photon energy range. Two classes of photon-stimulated charge-transfer processes, i.e., resonant processes via the formation of highly excited states of the condensed molecules and nonresonant processes involving energetic photoelectrons, are considered to account for these observations. PACS numbers: 31.70. Ks, 33.80.Eh, 68.45.Da, 79.20.Ds The charge-transfer process is of fundamental importance to many areas of biology and chemistry. For adsorbed molecules, photon-induced charge transfer may occur either directly by exciting molecular chargetransfer (ion-pair) states or indirectly by attaching a photoemitted electron (issued from the substrate or neighbor adsorbed species) onto the studied molecule. Photonstimulated charge transfer (PSCT) has been suggested by several authors [1,2] to play an important role in surface photochemistry although no direct evidence of PSCT has been obtained so far.The aim of this paper is to demonstrate, by using multilayers of condensed O2 as an example, that negative-ion desorption is a powerful and direct probe of PSCT in adsorbed molecules. The only previously reported observation of negative-ion desorption following photon excitation is that of negative H ~ ions from a cesiated W(100) surface by Hurych et al. [3]. However, in this case the absence of any variation of the desorption signal with photon energy prevented these authors from identifying particular desorption mechanisms. Negative-ion desorption from a number of adsorbed molecules was studied by electron impact [4][5][6]. Attention was focused on the dissociative attachment of slow electrons on physisorbed or chemisorbed molecules [5].In this Letter, we report the first study of photonstimulated desorption of negative ions from condensed gases involving intramolecular charge-transfer (ion-pair) states and intermolecular electron transfer. During the course of this work, observed for the first time photon-stimulated desorption of negative ions from condensed molecules produced by charge transfer from the substrate.Synchrotron radiation from Super-ACO at Orsay, dispersed by a grazing-incidence monochromator, is used as a photon source of variable energy in the 17-42-eV energy range with a 0.5-A bandpass. The experiments are performed in an UHV system reaching pressures below 10 _,° mbar. The molecular films are obtained by condensing O2 on a polycrystalline platinum substrate cooled at 15 K with a liquid-helium flow cryostat. The platinum substrate is thin enough (20 pm) to be resistively heated in order to be cleaned before any gas deposition. The film thickness of about five monolayers is estimated from photoabsorption measurements. Desorbed positive and negative ions are mass selected through a Riber SQX 156 quadrupole filter and counted as a function of the photon energy. Ion yields are normalized to the photon flux monitored by the photoemission of a gold mesh.The photodesorption yield of O ~ from condensed O2, r...

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“…], several excited states can contribute to the N ÿ 1 final state and result in a multiple-peak spectrum for an initial state. A well-known example is the PES of gas molecules [15,16]. The PES of H 2 molecules [15] shows multiple peaks, consisting of a ''0-0'' peak at a kinetic energy (E k ) of E 0 and sidebands at E k E 0 ÿ n!…”

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confidence: 99%

Temperature-Dependent Localized Excitations of Doped Carriers in Superconducting Diamond

et al. 2008

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Laser-excited photoemission spectroscopy is used to show that the doped carriers in metallic or superconducting diamond couple strongly to the lattice via high-energy (approximately 150 meV) optical phonons, with direct observations of localized Franck-Condon multiphonon sidebands appearing as Fermi-edge replicas. It exhibits a temperature-dependent spectral weight transfer from higher to lower energy sidebands and zero-phonon Fermi-edge states. The quantified coupling strength shows a systematic increase on lowering temperature, implicating its relation to the normal state transport and superconductivity.

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Ultraviolet Photoemission Spectroscopy of Solid Nitrogen and Oxygen

Cited by 64 publications

References 23 publications

Wavelength-dependent UV photodesorption of pure N₂and O₂ices

Wavelength-dependent UV photodesorption of pure N₂and O₂ices

Photon-stimulated charge transfer in condensedO2studied by negative-ion desorption

Temperature-Dependent Localized Excitations of Doped Carriers in Superconducting Diamond

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Ultraviolet Photoemission Spectroscopy of Solid Nitrogen and Oxygen

Cited by 64 publications

References 23 publications

Wavelength-dependent UV photodesorption of pure N2and O2ices

Wavelength-dependent UV photodesorption of pure N2and O2ices

Photon-stimulated charge transfer in condensedO2studied by negative-ion desorption

Temperature-Dependent Localized Excitations of Doped Carriers in Superconducting Diamond

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Wavelength-dependent UV photodesorption of pure N₂and O₂ices

Wavelength-dependent UV photodesorption of pure N₂and O₂ices