Continuous Emission Spectra of Rare Gases in the Vacuum Ultraviolet Region

Optimizing the performance of bandpass photon detectors for inverse photoemission: Transmission of alkaline earth fluoride window crystals

Bandpass photon detectors are widely used in inverse photoemission in the isochromat mode at energies in the vacuum-ultraviolet spectral range. The energy bandpass of gas-filled counters is usually formed by the ionization threshold of the counting gas as high-pass filter and the transmission cutoff of an alkaline earth fluoride window as low-pass filter. The transmission characteristics of the window have, therefore, a crucial impact on the detector performance. We present transmission measurements in the vacuum-ultraviolet spectral range for alkaline earth fluoride window crystals in the vicinity of the transmission cutoff as a function of crystal purity, surface finish, surface contamination, temperature, and thickness. Our findings reveal that the transmission characteristics of the window crystal and, thus, the detector performance depend critically on these window parameters.

Pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy of metastable He2: Ionization potential and rovibrational structure of He2+

A supersonic beam of metastable He(*) atoms and He(2) (*) a (3)Sigma(u) (+) molecules has been generated using a pulsed discharge at the exit of a pulsed valve prior to the gas expansion into vacuum. Pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the He(2) (+) X(+) (2)Sigma(u) (+) (v(+)=0-2)<--He(2) (*) a (3)Sigma(u) (+) (v(")=0-2) transitions and photoionization spectra of He(2) (*) in the vicinity of the lowest ionization thresholds have been recorded. The energy level structures of (4)He(2) (+) X(+) (2)Sigma(u) (+) (v(+)< or =2,N(+)< or =23) and (3)He(2) (+) X(+) (2)Sigma(u) (+) (v(+)=0,N(+)< or =11) have been determined, and an accurate set of molecular constants for all isotopomers of He(2) (+) has been derived in a global analysis of all spectroscopic data reported to date on the low vibrational levels of He(2) (+). The analysis of the photoionization spectrum by multichannel quantum defect theory has provided a set of parameters describing the threshold photoionization dynamics.

Rydberg states of the rare gas dimers

This work is dedicated to Gerhard Herzberg and his prodigious contributions to molecular spectroscopy. Of particular relevance here is Herzberg's seminal 1987 article (Annu. Rev. Phys. Chem. 38, 27 (1987)) in which he discussed the electronic structures of several groups of molecules he termed "Rydberg molecules". Among these are the rare gas dimers (Rg2), a group whose study has benefited significantly from recent advances in laser excitation and synchrotron-based spectroscopies, as well as in theory. Following the spirit of Herzberg's 1987 article, this paper reviews some of the more prominent features of Rydberg states in the Rg2 family as viewed from the current perspective.Key words: rare gas dimers, rare gas dimer excited states, Rg2 electronic structures, Rydberg states of He2, Ne2, Ar2, Kr2, and Xe2, electronic states of He2, Ne2, Ar2, Kr2, and Xe2.

Light emission of sonoluminescent bubbles containing a rare gas and water vapor

We present numerical simulations of sonoluminescent rare-gas bubbles in water, which account for (i) time variations of the water vapor content, (ii) chemical reactions, and (iii) the ionization of the rare gas and the H2O dissociation products. Peak temperatures exceed 10 000 K at densities of a few hundred amagat ( approximately 10(28) particles per m(3)). The gas mixture in the bubble is weakly ionized. Our model accounts for the light emission by electron-atom, electron-ion, and ion-atom bremsstrahlung, recombination radiation, and radiative attachment of electrons to hydrogen and oxygen atoms, which are all more or less important for single bubble sonoluminescence. Spectral shapes, spectral intensities, and durations of the light pulses are computed for helium, argon, and xenon bubbles. We generally obtain good agreement with the observations for photon numbers and pulse durations. Some calculated spectral profiles agree, however, less well with observations, especially in the case of the low water temperature and for helium bubbles. We try to identify the reasons why computed and observed spectral profiles might discernibly differ when all other computed features considered here seem to be quite consistent with observations. We show that by allowing the bubble to heat somewhat nonisotropically, agreement between observed and computed spectral profiles may be obtained, even in the case of helium bubbles at freezing water temperatures. In this case, charge exchange radiation and related processes involving helium atoms and ions become important.

Vacuum ultraviolet Mach-Zehnder interferometer with CaF(2) optics

A VUV Mach-Zehnder interferometer has been equipped with CaF(2) optics. To test these, the hook method was used to measure the oscillator strength of the 146.9610-nm (1)S(0)-(3)P(0)(1) line of atomic xenon. The result, f = 0.244 +/- 0.015, is in agreement with data obtained by other techniques. We conclude, as a result of this work, that application of our Mach-Zehnder interferometer to hook method measurements of oscillator strengths of lines with wavelengths longer than ~150 nm will be routine, but that such measurements below that wavelength limit must await development of more intense VUV continuum sources.

Light Sources in the 0.15-20-micro Spectral Range

The different kinds of light sources available for the 0.15-20-micro spectral range are surveyed. Information was obtained from the published literature, unpublished reports, light source manufacturers, and also from individual persons. The aim has been to present sufficient information, where available, to show the relative advantages of different sources-intensity, stability, and output uniformity were of prime interest. Continuum and line sources are included but lasers and pulsed sources are omitted. The sources are described under the main headings: Arc Discharge Sources, Glow Discharge Sources, and Incandescent Sources, with another section, Miscellaneous Sources, to cover some which could not be included under the first three headings.