Ultraviolet vacuum

Other atoms and molecules also show similar series of lines, often in the vacuum ultraviolet region, which fit approximately a similar fonuula ... 

Three-photon absorption has also been observed by multiphoton ionization, giving Rydberg states of atoms or molecules [36]. Such states usually require vacuum ultraviolet teclmiques for one-photon spectra, but can be done with a visible or near-ultraviolet laser by tluee-photon absorption. 

Herzberg G, Lagerquist A and Malmberg C 1969 New electronic transitions of the C2 molecule absorption in the vacuum ultraviolet region Can. J. Phys. 47 2735-43... 

This teclnhque can be used both to pennit the spectroscopic detection of molecules, such as H2 and HCl, whose first electronic transition lies in the vacuum ultraviolet spectral region, for which laser excitation is possible but inconvenient [ ], or molecules such as CH that do not fluoresce. With 2-photon excitation, the required wavelengdis are in the ultraviolet, conveniently generated by frequency-doubled dye lasers, rather than 1-photon excitation in the vacuum ultraviolet. Figure B2.3.17 displays 2 + 1 REMPI spectra of the HCl and DCl products, both in their v = 0 vibrational levels, from the Cl + (CHg) CD reaction [ ]. For some electronic states of HCl/DCl, both parent and fragment ions are produced, and the spectrum in figure B2.3.17 for the DCl product was recorded by monitoring mass 2 (D ions. In this case, both isotopomers (D Cl and D Cl) are detected. 

Hepburn J W 1995 Generation of coherent vacuum ultraviolet radiation applications to high-resolution photoionization and photoelectron spectroscopy Laser Techniques in Chemistry vol 23, ed A B Myers and T R Rizzo (New York Wley) pp 149-83... 

The homonuclear rare gas pairs are of special interest as models for intennolecular forces, but they are quite difficult to study spectroscopically. They have no microwave or infrared spectmm. However, their vibration-rotation energy levels can be detennined from their electronic absorjDtion spectra, which he in the vacuum ultraviolet (VUV) region of the spectmm. In the most recent work, Hennan et al [24] have measured vibrational and rotational frequencies to great precision. In the case of Ar-Ar, the results have been incoriDorated into a multiproperty analysis by Aziz [25] to develop a highly accurate pair potential. 

As for the far-infrared, absorption by air in the vacuum-ultraviolet (VUV) necessitates evacuation of the optical path from source to detector. In this region it is oxygen which absorbs, being opaque below 185 nm. 

Instead of using a laser operating in the vacuum-ultraviolet region a laser operating at half the energy may be used. Then the ionization process in Figure 9.50(b) involves the... 

Optical windows of highly purified magnesium fluoride which transmit light from the vacuum ultraviolet (140 nm) into the infrared (7) are recommended for use as ultraviolet optical components for use in space exploration. 

J. A. R. Sampson, Techniques of Vacuum Ultraviolet Spectroscopy,JohnWHey 8c Sons, Inc., New York, 1967. 

A. N. Zaidef and E. Ya. Shreider, Vacuum Ultraviolet Spectroscopy, Humphrey Science PubHshers, Ann Arbor, Mich., 1970. 

MPI is especially valuable for elemental analyses with typical useful yield of 10 . Because SALI is laser-based, expected improvements over the next few years, in particular for vacuum-ultraviolet laser technology, should have a significant impact. High repetition rate Nd—YAG systems with sufficient pulse energy are already available to 50 Hz, and probably can be extended to a few hundred Hz. 

Ever brighter vacuum-ultraviolet sources are being developed that would further boost SPI sensitivity, which already is typically 10 useful yield general, sensitive elemental analysis would then also be available using SPI, making possible a single laser arrangement for both elemental and molecular SALE... 

Usually, the ultraviolet and visible regions of the spectrum are recorded. Many of the most intense emission lines lie between 200 nm and 400 nm. Some elements (the halogens, B, C, P, S, Se, As, Sn, N, and O) emit strong lines in the vacuum ultraviolet region (170-200 nm), requiring vacuum or purged spectrometers for optimum detection. 

X rays I Vacuum ultraviolet Visible Near infrared Infrared i ) V / 1... 

When the wavelengths exceed the values for which crystals are available, it is necessary to go to gratings, preferably in vacuum. The problems then begin to resemble those encountered in the vacuum ultraviolet region. 

Vacuum ultraviolet photoelectron spectroscopy of inorganic molecules. R. L. De Kock and D. R. Lloyd, Adv. Inorg. Chem. Radiochem., 1974,16, 66-107 (187). 

Enhancement of the total butene yield is observed when various additives whose ionization potential falls below about 9.4 e.v. are present during ethylene radiolysis (35). This is consistent with the above interpretation (Figure 2). In the vacuum ultraviolet photolysis of cyclobutane the yield of butenes varies with the ionization potential of the additives in the same way as observed here (12). The maximum enhancement corresponds closely to the yield of C4H8+, as expected from our mechanism. 

On the other hand, the formation of ethylene was ascribed mainly to the unimolecular decomposition of a neutral excited propane molecule. These interpretations were later confirmed (4) by examining the effect of an applied electrical field on the neutral products in the radiolysis of propane. The yields of those products which were originally ascribed to ion-molecule reactions remained unchanged when the field strength was increased in the saturation current region while the yields of hydrocarbon products, which were ascribed to the decomposition of neutral excited propane molecules, increased several fold because of increased excitation by electron impact. In various recent radiolysis 14,17,18,34) and photoionization studies 26) of hydrocarbons, the origins of products from ion-molecule reactions or neutral excited molecule decompositions have been determined using the applied field technique. However, because of recent advances in vacuum ultraviolet photolysis and ion-molecule reaction kinetics, the technique used in the above studies has become somewhat superfluous. 

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