Visible absorption and resonance Raman spectra of alkaline earth metal ozonides in argon and nitrogen matrices at 10 K

Optical and resonance Raman spectra of the reaction products of Mg, Ca, Sr, and Ba with ozone were observed in argon and nitrogen matrices. The visible spectra were characterized by strong, vibronically structured absorptions between 540 and 350 nm, and are assigned to the alkaline earth metal ozonides, $\text{A}{}^{\mathrm{+}}\text{O}{}_3{}^{\mathrm{?}}$. Vibrational analysis yielded ω₁′ and ω₁x₁ values of about 900 and 6 cm^?1, respectively, with only slight variation from metal to metal. Resonance Raman spectra consisted of a strong fundamental near 1020 cm^?1 and two overtones with decreasing intensity. Oxygen-18 substitution confirmed the vibrational assignments, which agree very well with the alkali metal ozonide spectra. These results suggest that the +1 oxidation state plays an important role in the chemistry of the alkaline earth metals under conditions where aggregation does not occur to favor the +2 state. A thorough search was made for absorptions due to the alkaline earth oxide species, but no bands were observed.     

Nucleation in superheated argon,krypton and xenon liquids

The superheating of condensed noble gases (argon, krypton, xenon) was investigated by the techniques of continuous heating of liquid specimen in a glass capillary. Experiments covered the pressure range 1–35 bar at the nucleation rates ≈10⁵ cm^-3 s^-1. The superheating data obtained here were compared with the results of calculations based on the Volmer-Becker-Döring-Zeldovich-Frenkel homogeneous nucleation theory. A good agreement between theory and experiment as well as the thermodynamic similarity of the studied substances with respect to the fluctuation nucleation was found.     

Equilibrium properties of crystalline argon,krypton and xenon

By assuming an interaction energy for krypton and xenon of the same shape as that established for argon in an earlier paper and without introducing any adjustable parameters, values of the equilibrium properties of the crystals have been calculated which agree with the measured values to within the experimental accuracy or to within one per cent.     

Continuous emission of argon,krypton and xenon plasmas

Emission coefficients of shock-tube plasmas have been measured as functions of the plasma parameters in the visible spectrum. The plasma state was determined by dual-wavelength interferometry and high accuracy of the ξ-factors was achieved. The results are compared with theoretical and other experimental data. In particular, the dependence of ξ on the plasma state is discussed.     

Resonance fluorescence spectrum of nitrogen dioxide

We report an investigation of the resonance fluorescence spectrum of NO₂ excited by several laser lines. Sixty transitions, mostly in ν₂ progressions of the ground state, have been assigned. Analysis of the spectra extend the knowledge of the ground state constants, especially of the anharmonic coefficients. It is possible to establish that transitions are occurring to a ²B₁ state and to a ²B₂ state in the same energy region.     

On the dimerization of carbon dioxide in nitrogen and argon matrices

The ir spectrum of carbon dioxide in solid nitrogen and solid argon has been studied. In nitrogen, the NN stretching vibration becomes ir-active in the presence of carbon dioxide. Concentration dependency and diffusion studies allow the identification of a carbon dioxide dimer in solid argon. In solid nitrogen no clear evidence for a dimer was obtained.     

Photoionization of argon, krypton and xenon clusters in the inner valence shell region

Photoionization of rare gas clusters in the innervalence shell region has been investigated using threshold photoelectron and photoion spectrometers and synchrotron radiation. Two classes of states are found to play an important role: (A) valence states, correlated to dissociation limits involving an ion with a hole in its innervalence ns shell, (B) Rydberg states correlated to dissociation limits involving an ion with a hole in its outervalence np shell plus an excited neutral atom. In dimers, class A states are “bright”, that is, accessible by photoionization, and serve as an entrance step to form the class B “dark” states; this character fades as the size of the cluster increases. In the dimer, the “Mulliken” valence state is found to present a shallow potential well housing a few vibrational levels; it is predissociated by the class B Rydberg states. During the predissociation a remarkable energy transfer process is observed from the excited ion that loses its innershell electron to its neutral partner. Received: 10 February 1998 / Revised: 17 July 1998 / Accepted: 31 July 1998     

Derivation of three-body collision-induced light-scattering spectrum moments for argon,krypton, xenon

The expressions for the zeroth and second moments of the three-body component of the collision-induced light-scattering spectrum are derived within the pair-potential and pair-polarizability approximations.

Computer calculation of the three-dimensional integrals which appear in the moment expressions is performed for Lennard-Jones and Barker potentials of argon, krypton and xenon within the dipole-induced-dipole approximation for the pair-polarizability.

The comparison of the results which are obtained with the two different potentials shows the very important role which is played by the choice of the potential in the determination of the values of the moments. An example of the applicability of the moment analysis of the three-body spectrum is also given for argon and the results compared with those of two-body.     

Environmental perturbations on foreign atoms and molecules in solid argon,krypton and xenon

Perturbations which are responsible for the shifts of electronic and vibrational spectra of species trapped in a solid are considered in terms of the intermolecular potential which describes interactions between these species and neighbouring atoms. It is shown that in certain instances London's theory can give an adequate approximation to the dispersion energy between an electronically excited species and a rare gas atom. The experimental shifts in the electronic absorption spectra of Hg, NH and C₂ at lattice sites in rare gas crystals at 4·2°k are explained quantitatively on the basis of a Lennard-Jones (6-12) or (6-8-12) potential between the trapped species and the rare gas atoms. The theory does not adequately explain the shifts in those cases where strong angular dependent forces differing appreciably in the two electronic states are present, data on trapped NH₂ free radicals being presented as a case in point. The interaction of sodium atoms with argon at 4·2°k is very complex, the data being consistent with multiple trapping sites for the atoms, a large repulsive interaction between the excited state of sodium and the rare gas, and apparent removal of the three-fold orbital degeneracy in the excited state by the environmental perturbation. The three-fold orbital degeneracy in the ³P₁ state of mercury was found also to be removed. The blue shift of 1281 cm^-1 for the ³P₁ ← ¹S₀ transition of mercury in solid argon at 4·2°k corresponds almost exactly with the position of one of the two prominent features in the spectrum of mercury in argon gas at comparable densities and illustrates the similarity of structure in the two physical states. The interesting perturbations on the vibrational states of NH and C₂ suggest a close similarity to the effect which causes environmental variations of coupling constants for hyperfine interactions in trapped hydrogen atoms.     

Optical absorption spectra of K41-atoms isolated in argon matrices

High purity argon polycrystals were doped with 0.2 ppm of K⁴¹ through the nuclear reaction Ar⁴⁰(n, ^–)K⁴¹. Optical transmission was measured as a function of the annealing temperature between 300 nm and 800 nm. Absorption bands corresponding to the transitions 4² p _{1/2, 3/2}4² s _1/2 and 5² p _{1/2, 3/2}4² s _1/2 of free potassium atoms could be observed. Annealing dependence of these absorption bands was studied and may be understood by a simple model.Research supported by Bundesministerium für Forschung und Technologie under FV. 4MT/1L     

Resonance absorption and fluorescence in argon

Absorption cross sections of argon for argon resonance radiation have been measured by several techniques. The apparent cross sections are small (0·1 to 1·6 × 10^-18 cm²) for resonance absorption and the values depend on the technique used for measurement. These observations are interpreted in terms of extensive reversal and broadening in the source. The excitation and quenching of resonance fluorescence was studied to provide information about the rates of the processes

The rate constants were estimated relative to k _r, the rate constant for radiation. Radiation imprisonment leads to a reduction of k _r from its natural value and observations of the decay of resonance fluorescence suggest that k _r ～ 1·5 × 10⁵ s^-1 in our system at [Ar] = 2 × 10¹⁷ atom cm^-3. Combining this value with the relative values for the quenching rate constants gives k ₁ < 1·5 × 10^-13, k ₁′(M = N₂) ～ 6 × 10^-12, k ₁′(M = NO) ～ 4 × 10^-10, in units of cm³ s^-1 molecule^-1.     

Resonance fluorescence of gaseous chlorine excited with a single longitudinal mode argon ion laser

Resonance fluorescence spectra of gaseous chlorine, excited with a high power single longitudinal mode argon ion laser which was tuned through the lasing profiles of the 4880-, 4965-, 5017-, and 5145-Å lines, were studied. Five progressions of fluorescence lines were found and assigned as the fluorescence of ³⁵Cl³⁵Cl and ³⁷Cl³⁷Cl isotopic molecules resonantly excited from v = 0 and 1 levels of the X¹Σ state to the B³Π state. The fluorescence line positions agreed with those of the theoretical calculation within 0.2 cm^?1. The fluorescence intensities were very weak due to the extremely small transition probability between the B³Π and the X¹Σ states.     

Elementary vibrations in rare-gas crystals: Frequencies of phonons in compressed argon, krypton, and xenon crystals

The lattice dynamics of rare-gas crystals is investigated in the framework of the ab initio approach with the inclusion of the nonadiabatic effects over a wide range of pressures. The frequencies of phonons in argon, krypton, and xenon crystals are calculated at pressures p ≠ 0. Analysis of the contributions from different interactions to the lattice dynamics of the crystals demonstrates that the difference between the phonon frequencies calculated within several models is most pronounced at the boundary of the Brillouin zone. Under strong compressions, the phonon spectrum along the Δ direction is distorted and the longitudinal mode is softened as a result of the electron-phonon interaction, with the relative contribution decreasing in the series Ar, Kr, and Xe. The calculated phonon frequencies are in good agreement with the experimental data available in the literature for argon crystals at a pressure p = 3.1 GPa.     

High-pressure melting curves of argon, krypton, and xenon: deviation from corresponding states theory.

The melting curves of argon, krypton, and xenon were measured in a laser heated diamond-anvil cell to pressures of nearly 80 GPa reaching melting temperatures around 3300 K. For the three gases, we observed a considerable decrease in the melting slopes (dT/dP) from the predictions based on corresponding states scaling starting near 40, 30, and 20 GPa, respectively. The melting anomaly can be understood in terms of a model in which hcp stacking faults act as solutes in a binary system.     

Ultraviolet absorption spectra of Zn2 and Cd2 in solid argon and krypton at 10 K

Zinc and cadmium atoms have been condensed with argon and krypton at 10 K. The most intense absorption is due to the ${}^1\text{P}{}_1\text{←}{}^1\text{S}{}_0$ atomic transition, and a weak band is due to the ${}^3\text{P}{}_1\text{←}{}^1\text{S}{}_0$ atomic absorption. Structured absorptions at 252 and 254 nm in solid argon and krypton with vibrational spacings of 140-120 cm^?1 are due to the ${}^1\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}\text{←}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ transition of Zn₂. Similar 273 and 277 nm absorptions with 110-90 cm^?1 vibrational spacings are due to Cd₂ in solid argon and krypton, respectively.     

Emission and excitation spectra of IF in solid argon at 12 K

The interhalogen, IF, has been synthesized by vacuum ultraviolet photolysis of CHF₂I and CHFI₂ and subsequently trapped in solid argon at 12 K. The $\text{B}{}^3\text{π}{}_0{}^{\mathrm{+}}\text{-X}{}^1\text{Σ}$ transition was observed in emission and dye laser excitation experiments with the origin near 18 688 cm^?1 and average ground- and excited-state spacings of 573 and 380 cm^?1, respectively. These data are compared to the gas phase results.     

Diffusion cooling in neon,argon, and krypton afterglow plasmas

Measurements are reported of ambipolar diffusion coefficients as determined from ion density loss rates, and of electron temperatures determined using the single Langmuir probe technique, in afterglow plasmas of spectroscopically pure neon, argon and krypton. In each gas there was a critical pressure,p _{0 c} , above which the product of the ambipolar diffusion coefficient,D _a , and the reduced gas pressure,p ₀, was pressure independent and above which the electron temperature was found to cool asymptotically to the gas temperature. For pressures belowp _{0 c} ,D _a p ₀ decreased with decreasing pressure, and the electron temperature cooled asymptotically to a steady equilibrium value,T _eq, below the gas temperature, this equilibrium value itself decreasing with decreasing gas pressure. These results clearly show that diffusion cooling of electrons was taking place at these low gas pressures. A detailed study of the krypton afterglow showed that the values ofD _a p ₀ andT _eq for a given gas pressure were related in a manner predicted by simple diffusion theory. During the course of these measurements values for the zero field mobilities of Ne⁺, Ar⁺ and Kr⁺ ions in their parent gases were obtained and are also reported.     

Energy loss spectra of xenon and krypton and their analysis by energy-dependent multichannel quantum defect theory

Oscillator strengths of xenon and krypton for transitions from the ground state to the optically allowed states forming the five resonance series were measured by means of high energy electron spectroscopy (HEEIS). The rather irregular behaviour of these oscillator strengths is analyzed with the aid of the known atomic level energies by means of the energy-dependent quantum defect theory. With the parameters obtained by the analysis of the energy loss measurement autoionized lines shapes and the asymmetry parameter for the photoionizationβ of Kr and Xe were calculated in excellent agreement with experimental data from the literature. The comparison of the parameters and their energy dependence for Kr and Xe gives indication that some properties change rather rapidly from Kr to Xe. The theory enables also to predict missing term levels of Kr.