How To Work Up Ultraviolet Photoelectron Data

Ultraviolet photoelectron spectroscopy (UPS) refers to the measurement of kinetic free energy spectra of photoelectrons emitted past molecules which have captivated ultraviolet photons, in lodge to determine molecular orbital energies in the valence region.

Basic theory [edit]

If Albert Einstein's photoelectric law is applied to a free molecule, the kinetic energy ( $E_{1000}$ ) of an emitted photoelectron is given past

E_{G}=h\nu -I\,

where h is Planck'southward constant, ν is the frequency of the ionizing calorie-free, and I is an ionization free energy for the germination of a singly charged ion in either the ground state or an excited land. According to Koopmans' theorem, each such ionization free energy may exist identified with the energy of an occupied molecular orbital. The basis-state ion is formed by removal of an electron from the highest occupied molecular orbital, while excited ions are formed by removal of an electron from a lower occupied orbital.

History [edit]

Prior to 1960, nigh all measurements of photoelectron kinetic energies were for electrons emitted from metals and other solid surfaces. In virtually 1956, Kai Siegbahn adult X-ray photoelectron spectroscopy (XPS) for surface chemical analysis. This method uses x-ray sources to report energy levels of atomic core electrons, and at the time had an energy resolution of nigh ane eV (electronvolt).^[one]

UPS in the gas stage, IPREM, Pau, France, Dr. JM Sotiropoulos, CNRS

The ultraviolet photoelectron spectroscopy (UPS) was pioneered by Feodor I. Vilesov, a physicist at St. petersburg (Leningrad) State University in Russian federation (USSR) in 1961 to study the photoelectron spectra of free molecules in the gas phase.^[2] ^[3] The early experiments used monochromatized radiation from a hydrogen discharge and a retarding potential analyzer to measure the photoelectron energies. The Human foot was further developed past David W. Turner, a concrete chemist at Imperial College in London then at Oxford University, in a series of publications from 1962 to 1967.^[4] ^[5] As a photon source, he used a helium discharge lamp which emits a wavelength of 58.4 nm (corresponding to an free energy of 21.2 eV) in the vacuum ultraviolet region. With this source, Turner's group obtained an energy resolution of 0.02 eV. Turner referred to the method as "molecular photoelectron spectroscopy", now usually "ultraviolet photoelectron spectroscopy" or UPS. As compared to XPS, UPS is express to energy levels of valence electrons, but measures them more accurately. After 1967, commercial UPS spectrometers became available.^[6] One of the latest commercial devices was the Perkin Elmer PS18. For the final 20 years, the systems take been bootleg. One of the latest in progress - Phoenix Two - is that of the laboratory of Pau, IPREM adult by Dr. Jean-Marc Sotiropoulos.^[seven]

Awarding [edit]

The UPS measures experimental molecular orbital energies for comparison with theoretical values from quantum chemistry, which was also extensively developed in the 1960s. The photoelectron spectrum of a molecule contains a serial of peaks each corresponding to i valence-region molecular orbital energy level. Also, the high resolution immune the observation of fine structure due to vibrational levels of the molecular ion, which facilitates the assignment of peaks to bonding, nonbonding or antibonding molecular orbitals.

The method was subsequently extended to the study of solid surfaces where it is usually described as photoemission spectroscopy (Human foot). Information technology is specially sensitive to the surface region (to 10 nm depth), due to the short range of the emitted photoelectrons (compared to 10-rays). It is therefore used to study adsorbed species and their bounden to the surface, too as their orientation on the surface.^[viii]

A useful result from characterization of solids by UPS is the decision of the work function of the material. An example of this determination is given by Park et al.^[9] Briefly, the total width of the photoelectron spectrum (from the highest kinetic energy/everyman binding energy point to the low kinetic energy cutoff) is measured and subtracted from the photon free energy of the exciting radiation, and the difference is the work office. Often, the sample is electrically biased negative to dissever the low free energy cutoff from the spectrometer response.

Gas discharge lines [edit]

Gas	Emission Line	Energy (eV)	Wavelength (nm)	Relative Intensity (%)
H	Lyman α	x.20	121.57	100
	Lyman β	12.09	102.57	10
He	1 α	21.22	58.43	100
	ane β	23.09	53.70	approx 1.v
	one γ	23.74	52.22	0.five
	2 α	twoscore.81	30.38	100
	ii β	48.37	25.63	<10
	2 γ	51.02	24.30	negligible
Ne	i α	xvi.67	74.37	15
	1 α	sixteen.85	73.62	100
	ane β	nineteen.69	62.97	< 1
	i β	19.78	62.68	< ane
	two α	26.81	46.24	100
	two α	26.91	46.07	100
	2 β	27.69	44.79	twenty
	2 β	27.76	44.66	20
	two β	27.78	44.63	20
	2 β	27.86	44.51	xx
	2 γ	30.45	twoscore.71	twenty
	two γ	30.55	forty.58	20
Ar	1	eleven.62	106.70	100
	1	11.83	104.fourscore	50
	2	thirteen.30	93.22	30
	2	13.48	91.84	fifteen

Outlook [edit]

UPS has seen a considerable revival with the increasing availability of synchrotron calorie-free sources which provide a wide range of monochromatic photon energies.

See too [edit]

Angle resolved photoemission spectroscopy ARPES
Photoelectron photoion coincidence spectroscopy PEPICO
Time-resolved ii-photon photoelectron spectroscopy

References [edit]

^ Carlson T.A., "Photoelectron and Auger Spectroscopy" (Plenum Press, 1975) ISBN 0-306-33901-3
^ Vilesov, F. I.; Kurbatov, B. Fifty.; Terenin, A. North. (1961). "Electron Distribution Over Energies In Photoionization Of Effluvious Amines in Gaseous Phase". Soviet Physics Doklady. half dozen: 490. Bibcode:1961SPhD....6..490V.
^ Price, West. C. (1974). "Photoelectron Spectroscopy". Advances in Atomic and Molecular Physics. 10: 131. Bibcode:1974AdAMP..10..131P. doi:10.1016/S0065-2199(08)60348-vi. ISBN9780120038107.
^ Rabalais J.Due west. "Principles of Ultraviolet Photoelectron Spectroscopy" (Wiley 1977) ISBN 0-471-70285-4
^ Turner, David W. (1970). Molecular photoelectron spectroscopy. London: Wiley Interscience. ISBN0-471-89320-10. OCLC 108745.
^ Baker, Arthur D.; Betteridge, David (1972). Photoelectron Spectroscopy. Chemical and Analytical Aspects (Showtime ed.). Oxford: Pergamon Press. ISBN0-08-016910-4. OCLC 539873.
^ mdomingo#utilisateurs (2020-09-x). "Jean-Marc Sotiropoulos". iprem.univ-pau.fr (in French). Retrieved 2021-05-17 .
^ Peter Due west. Atkins and Julio de Paula "Physical Chemistry" (Seventh edition, W.H.Freeman, 2002), p.980 ISBN 0-7167-3539-3
^ Park, Y.; Choong, V.; Gao, Y.; Hsieh, B. R.; Tang, C. W. (1996-05-06). "Work office of indium tin can oxide transparent conductor measured past photoelectron spectroscopy". Applied Physics Letters. 68 (xix): 2699–2701. Bibcode:1996ApPhL..68.2699P. doi:x.1063/1.116313. ISSN 0003-6951.