SIMS,AES, work function and flash desorption measurements of the CO adsorption on NiCu alloy surfaces

The chemisorption of CO on Cu, Ni and CuNi alloy surfaces was examined by SIMS, work function measurements and desorption spectroscopy. Using a dynamic SIMS technique the M⁺, M⁺₂, MCO⁺ and M₂CO⁺ emission at different temperatures (100–400 K) was measured as a function of CO exposure. In agreement with the work function and desorption experiments an increase of M⁺ and MCO⁺ emission due to the CO adsorption on Cu was found only at low temperatures (100–190 K). On the Ni surface an increase of Ni⁺, NiCO⁺ and Ni₂CO⁺ was measured up to 400 K. The adsorption of CO on CuNi alloy surfaces — as derived from the work function measurements — can be described by the assumption of two different states of adsorbed carbon monoxide. They can be characterized by different binding energies and from sign and magnitude different work function changes. These states were interpreted as adsorption at Ni or Cu sites of the alloy surfaces, respectively. To a certain extent the SIMS results from the alloy surfaces are incompatible with the work function measurements and desorption spectroscopy and the SIMS studies on the pure metals. A Cu⁺ emission with comparable intensity to the Ni⁺ emission was found for alloys with bulk concentrations of 60 and 40 at% Cu at 300 K. The ratio $\text{Ni}{}^{\mathrm{+}}\text{Cu}{}^{\mathrm{+}}$ was nearly independent of CO pressure and temperature. The measured ratios of $\text{Cu}{}^{\mathrm{+}}{}_2\text{(}\text{Cu}{}^{\mathrm{+}}\text{+}\text{Ni}{}^{\mathrm{+}}\text{)}$, $\text{Ni}{}^{\mathrm{+}}{}_2\text{(}\text{Cu}{}^{\mathrm{+}}\text{+}\text{Ni}{}^{\mathrm{+}}\text{)}$ and $\text{CuNi}{}^{\mathrm{+}}\text{(}\text{Cu}{}^{\mathrm{+}}\text{+}\text{Ni}{}^{\mathrm{+}}\text{)}$ with values about 10^?2 can be explained the basis of a statistical arrangement of Cu and Ni atoms in the alloy surface. The intensities of the MCO⁺ emissions are 10² times smaller than the corresponding values of the pure metals. No emission of M₂CO⁺ was found on CuNi during CO adsorption.     

Dielectronic satellite spectra from dense laser-produced plasmas

The Lyman-α and adjacent dielectronic satellite lines have been observed in the spectra from laser-irradiated solid targets. In a carbon plasma from a planar target, the relative intensity of the $\text{2p}{}^2{}^3\text{P?1s2p}{}^3\text{P}$ satellite line of C(V) increases as a function of electron density in the range 8 × 10¹⁹ to 2 × 10²⁰ cm^?3. As analysis of a series of imploded microballoon experiments indicates that the $\text{2p}{}^2{}^3\text{P?1s2p}{}^3\text{P}$ and $\text{2s2p}{}^3\text{P?1s2s}{}^3\text{S}$ satellite radiation of Si(XIII) increases for electron densities 1 × 10²²?2 × 10²³ cm^?3. The satellite intensity distributions have been numerically simulated using a rate equation model. It is shown that the carbon and silicon satellite data may be interpreted in a consistent manner, and the extension to higher atomic numbers Z and higher electron densities is considered.     

Two-electron,one-photon transitions in nickel

The two emission lines, Kα₁α₃^h and Kα₂α₃^h resulting from the two-electron transitions $\text{1s}{}^{\mathrm{?2}}\text{→ 2s}{}^{\mathrm{?1}}\text{2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$ and $\text{1s}{}^{\mathrm{?2}}\text{→ 2s}{}^{\mathrm{?1}}\text{2p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$ were resolved for elemental nickel. Their measured energies agree well with calculations. Their relative intensity $\text{I(Kα}{}_1\text{α}{}_3{}^{\mathrm{h}}\text{)/I(Kα}{}_2\text{α}{}_3{}^{\mathrm{h}}\text{) ≈}\text{3}\text{4}$ and their intensity relative to that of the Kα diagram lines is about 10^?4. This is some 10⁴ times larger than both theoretical results and the results of ion-atom collision experiments.     

The second 132+ state in 19F

A cryogenically pumped gas target has been used to study resonances in the ¹⁵N(α, γ)¹⁹F reaction for E_α = 5.1 to 8.6 Mev. Gamma-ray intensity and angular distribution measurements for a resonance at E_α = 8.105 Mev, corresponding to a state at 10.411 MeV in ¹⁹F, restrict the spin and parity of the state to $\text{11}\text{2}{}^{\mathrm{+}}$ or $\text{13}\text{2}{}^{\mathrm{+}}$. Comparison with shell model calculations indicate that the state is a strong candidate for the second $\text{13}\text{2}{}^{\mathrm{+}}$ (2s, 1d)³ level in ¹⁹F.     

Characteristics of target interaction with high power UV laser radiation

Thermal conduction, mass ablation rate, pressure and preheat were investigated in the interaction of a frequency tripled Nd: glass laser of power 0.-0.2 TW with flat targets. In the range $\text{10}{}^{13}\text{?10}{}^{15}\text{W}\text{cm}{}^2$ for 400 ps pulses we find: (a) thermal conduction may be described by a flux limiter f = 0.04 ± 0.01; (b) the mass abaltion rate depends on the incident laser irradiance as $\text{m}\text{?}\text{= 4.4 × 10}{}^5\text{(I/10}{}^{14}\text{)}{}^{0.53}\text{g cm}{}^{-2}\text{s}{}^{-1}$; (c) the pressure near the ablation surface increases approximately linearly with irradiance and is about 70 Mbar at 10¹⁵ W/cm², and (d) preheat as evidenced by K_α X-ray line emission is significantly lower than in λ = 1.05 μm irradiation.     

The ground state of methane 12CH4 through the forbidden lines of the ν3 band

High resolution spectra of the ν₃ band of methane, ¹²CH₄, were recorded by using a “third generation vacuum Fourier interferometer”; a large pressure range (from 0.009 to 10 Torr) with a sample path fixed at eight meters was used, enabling observation of transitions with intensity ratios as low as $\text{1}\text{10 000}$. More than 350 forbidden transitions of the ν₃ band, including about 125 transitions of the Q⁺ branch, were unambiguously identified. Of the 277 transitions retained for computations, one-hundred have 11 ≤ J ≤ 16. From combination difference relations using pairs of transitions having the same upper state energy level (forbidden-allowed and forbidden-forbidden pairs were used), 276 independent differences between ground state energy levels could be determined with uncertainties of about 0.001 cm^?1.These data yielded the following values for the ground state structure constants of ¹²CH₄ along with their standard deviations (in cm^?1): $\text{β}{}^{\mathrm{o}}\text{hc}\text{=5.2410356±0.0000096}$, $\text{γ}{}^{\mathrm{o}}\text{hc}\text{=(?1±0.00074) 10}{}^{\mathrm{?4}}$, $\text{π}{}^{\mathrm{o}}\text{hc}\text{=(5.78±0.18) 10}{}^{\mathrm{?9}}$, $\text{?}{}^{\mathrm{o}}\text{hc}\text{=(?1.4485±0.0023) 10}{}^{\mathrm{?6}}$, $\text{?}{}^{\mathrm{o}}\text{hc}\text{=(1.768±0.126) 10}{}^{\mathrm{?10}}$, $\text{ξ}{}^{\mathrm{o}}\text{hc}\text{=(?1.602±0.067) 10}{}^{\mathrm{?11}}$, Thus, for the first time, the scalar constant π⁰ has been evaluated and ir values have been obtained for the two tetrahedral constants ?⁰ and ξ⁰; furthermore, these values are in very good agreement with the ones recently determined from radiofrequency data, i.e., in cm^?1: $\text{?}{}^{\mathrm{o}}\text{hc}\text{=(?1.45061±0.00014) 10}{}^{\mathrm{?6}}$, $\text{?}{}^{\mathrm{o}}\text{hc}\text{=(1.7634±0.0068) 10}{}^{\mathrm{?10}}$, $\text{ξ}{}^{\mathrm{o}}\text{hc}\text{=(?1.5432±0.0040) 10}{}^{\mathrm{?11}}$ From these values, the 276 differences can be reproduced with an overall rms deviation equal to 0.0009 cm^?1.Finally, the ground state energies of ¹²CH₄ have been calculated for J ≤ 16.     

Pressure broadening,lineshapes, and intensity measurements in the 2 ← 0 band of NO

Lineshape and intensity measurements were made on the overtone band (v = 2 ← 0) of nitric oxide (NO) using a tunable difference-frequency laser system. Self- and N₂-pressure broadening coefficients were obtained at 296 K, and a small amount of collisional, or Dicke, narrowing (which reduces the Doppler width by ～9% at 50 Torr) was also evident. The pressure broadening observed for the ${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ transitions was larger than that of the ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for corresponding J by about 7%, so an empirical scaling law model was fit to the broadening coefficients to determine the role of interstate (spin-flipping) collisions. A small collision-induced asymmetry in the Λ-doublet transitions of the ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ level was also observed. The measured line intensities yield an integrated band intensity of 1.878(_?40⁺⁹⁰) cm^?2 atm^?1 at 296 K and a Herman-Wallis F factor which determines the relative signs of terms in the dipole moment expansion.     

Excitation intensity dependence of shallow donor bound exciton luminescence in n-GaAs

Luminescence measurements were performed on high purity epitaxial n-GaAs $\text{(}\text{1 × 10}{}^{14}\text{cm}{}^3\text{< n <}\text{3 × 10}{}^{15}\text{cm}{}^3\text{)}$ for various excitation intensities I₀ in the range $\text{8 mW}\text{cm}{}^2\text{< I}{}_0\text{<}\text{4 W}\text{cm}{}^2$. The luminescence line corresponding to the radiative decay of the shallow donor bound exciton, (D⁰, X), broadens with increasing I₀ and appears as a doublet for $\text{I}{}_0\text{? 1}\text{W}\text{cm}{}^2$, while the two-electron replica of the (D⁰, X) remains a single narrow line. The doublet structure of the (D⁰, X) at elevated excitation levels is due to missing luminescence intensity in the center of the line as a consequence of low (D⁰, X) concentration in a layer extending 1–2 μm from the sample surface into the bulk. The low concentration of (D⁰, X) is attributed to capture of (D⁰, X) quanta into surface states, extending to lower energies from the Fermi level fixed by the shallow donors. Comparison of the present results with luminescence spectra obtained by various authors reveals, that unexplained spectral features in the (D⁰, X) region of n-GaAs reported in the literature are a consequence of high excitation intensity and correspond to the effect reported here. In partly compensated p-GaAs with donor concentrations as given above, the (D⁰, X) did not transform into a doublet structure even at $\text{W}\text{cm}{}^2$ excitation intensity.     

Predissociated rotational structure in the 2490-Å band of 15NO2

The rotational structure of the 000-000 band of the 2490-Å system of ¹⁵NO₂ ($\text{2}{}^2\text{B}{}_2\text{-}\text{X}\text{?}{}^2\text{A}{}_1$) has been analyzed from high dispersion grating spectrograph plates. The band is found to be slightly predissociated, exactly as in the ¹⁴NO₂ isotope, which suggests that it might be usable for laser separation of the isotopes of nitrogen; tables of the wavenumbers of the lines are given. The upper-state molecular constants are close to the values calculated by the isotope relations from those of ¹⁴NO₂.     

Multiphonon relaxation rate from pumped level to upper laser level in YAG:Nd

The rise time of the near-infrared fluorescence intensity has been measured in YAG:Nd³⁺ at room temperature under the excitation by 10 ns duration pulses at 514.5 nm using a time-correlated single photon counting method. The result reveals that the relaxation rate from the pumped level (${}^2\text{K}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ + ${}^2\text{G}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ + ${}^4\text{G}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}$ to the upper level laser level $\text{(}{}^4\text{F}{}_{\mathrm{<mtext>sol3</mtext><mtext>2</mtext>}}\text{)}$ is larger than 10⁸s^?1, which is in contrast with the previously reported values of (1.6 ～ 2) × 10⁶s^?1. An experiment to search for the visible emission in YAG:Nd³⁺ gives support to the present value.     

Structure of positive parity states in 29P and two-step processes in (p,t) reactions

From a study of (p,t) reactions on ³¹P and ³⁰Si it is suggested that in ²⁹P the states with $\text{J}{}^{\mathrm{\pi }}\text{=}\text{1}\text{2}{}_1{}^{\mathrm{+}}$ and $\text{1}\text{2}{}_2{}^{\mathrm{+}}$, the pair $\text{3}\text{2}{}_2{}^{\mathrm{+}}$, $\text{5}\text{2}{}_1{}^{\mathrm{+}}$, and the pair $\text{7}\text{2}{}_3{}^{\mathrm{+}}$, $\text{9}\text{2}{}_1{}^{\mathrm{+}}$ are related by weak coupling of a s${}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ proton with the states 0₁⁺, 0₂⁺, 2₁⁺ and 4₁⁺ respectively of ²⁸Si. Completely atypical L = 2 angular distributions have been obtained for the $\text{3}\text{2}{}_1{}^{\mathrm{+}}$ and $\text{5}\text{2}{}_2{}^{\mathrm{+}}$ states in ²⁹P and it is suggested that this is due to contribution by two-step processes.     

Ω− produced in K−p reactions at 4.2 GeV/c

Forty $\text{Ω}{}^{\mathrm{?}}$ events have been observed in a large (133 events/βb) experiment at 4.2 GeV/c incident K^? momentum. Thirty nine of the events come from the three-body reaction $\text{K}{}^{\mathrm{?}}\text{p}\text{→Ω}{}^{\mathrm{?}}\text{K}{}^{\mathrm{+}}\text{K}{}^0$. The $\text{Ω}{}^{\mathrm{?}}$ is mainly produced in the forward hemisphere (direction of the incident K^?). The lifetime is measured to be τ = (0.75 _+0.14?0.11 × 10^?10 sec substantially less than the Particle Data Group value of (1.3 _?0.3^+0.2) × 10^?10 sec. The mass is determined to be 1671.7 ± 0.6 MeV, in good agreement with other determinations. The decay asymmetry parameter α (for the decay mode $\text{Ω}{}^{\mathrm{?}}\text{→ Λ}\text{K}{}^{\mathrm{?}}$) is found to be ?0.2 ± 0.4.     

Spectral properties of a HgBr2 photodissociation laser

A small-size HgBr₂ photodissociation laser is operated without buffer gas. It is shown, that in the laser emission as well as in the flourescence spectrum, excited with the wavelength of an ArF laser at 193 nm, approximately the 10 lowest-lying vibrational levels of the $\text{B}{}^2\text{Σ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{+}}$ state contribute to the emission.     

The visible absorption spectrum of NO2: A three-mode nuclear dynamics investigation

The vibronic band origins of the visible absorption spectrum of NO₂ are calculated theoretically with the aid of a simple model Hamiltonian for the coupled electronic and vibrational motions. Including all three vibrational modes in the calculation and using ab initio values of the relevant parameters, we obtain satisfactory qualitative agreement with experiment. In particular, the observed high density and irregular intensity distribution of the band origins is reproduced correctly by the calculation. The present results confirm unambiguosly that the anomalous vibronic structure of the ${}^2\text{B}{}_2\text{←}{}^2\text{A}{}_1$ transition is caused by strong nonadiabatic interactions between the ²B₂ and ²A₁ electronic states of NO₂. They also show that simple deconvolution procedures, which are often used to deperturb irregular spectra, are not applicable to the ${}^2\text{B}{}_2\text{←}{}^2\text{A}{}_1$ transition of NO₂. To further explore the strength of the nonadiabatic effects in NO₂, we calculate the mixing of the different electronic species in the vibronic eigenstates and compare it to several relevant experimental quantities.     

The isothermal kinetics of hydrogen adsorption onto iron films observed with the chemisorption-induced resistance change

A study has been made of the isothermal kinetics for hydrogen chemisorption onto evaporated thin iron films. The measurements were made over a temperature range from about 293 to 460 K and for hydrogen pressures up to about $\text{10}{}^{\mathrm{?2}}\text{N}\text{m}{}^2\text{(8 × 10}{}^{\mathrm{?5}}\text{Torr}\text{)}$. The chemisorption kinetics were measured using the chemisorption-induced resistance change to monitor the coverage of the chemisorbed hydrogen as it responded to changes in the gas phase pressure. Data from the measurements (adsorption kinetics, desorption kinetics, pressure-jump relaxation kinetics, and equilibrium isotherms) were analyzed in terms of a simple chemical reaction kinetic model which assumes that dissociative chemisorption occurs via an adsorbed molecular state. The absolute rate constants of the model obtained in this analysis were found to be independent of coverage for estimated coverages less than 0.8 monolayers. Based on the model, the desorption process in this temperature range is rate limited by desorption from the adsorbed molecular state to the gas phase.     

Neutron-proton radius differences and isovector deformations from π+ and π− inelastic scattering from 18O

π⁺ and π^? elastic and inelastic scattering from ¹⁸O have been measured at T(π)=164 MeV. Consistent with the results at 230 MeV, it is found that the ratio $\text{σ(π}{}^{\mathrm{?}}\text{)}\text{σ(π}{}^{\mathrm{+}}\text{)}$ for the 2₁⁺ state is 1.86(16), while for the 3₁^? state it is 0.89(6). These results are interpreted as indicating differences in neutron and proton deformations characterizing the 2₁⁺ transition and partial neutron blocking for the 3₁^? transition. Optical model analysis of elastic scattering leads to the conclusion that $\text{〈r}{}_{\mathrm{<mtext>n</mtext>}}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{?〈r}{}_{\mathrm{<mtext>p</mtext>}}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{=0.03(3)}\text{fm}$.     

Evidence for double dissociation in K-p interactions at 14.3 GeV/c

We have studied the reaction K^-p → K^-π⁺π^-π⁺π^-p at 14.3 GeV/c to search for evidence of the double dissociation process $\text{K}{}^{\mathrm{-}}\text{p}\text{→}\text{QN}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^1$. In the channel $\text{K}{}^{\mathrm{-}}\text{p}\text{→}\text{K}{}^{10}\text{(890)}$π₁^-π₂^-Δ⁺⁺ (1236) there is evidence for simultaneous production of low-mass enhancements in the $\text{K}{}^{10}\text{π}{}_1{}^{\mathrm{-}}$ and Δ⁺⁺(1236)π₂^- subsystems which correspond to the $\text{Q}\text{→}\text{K}{}^1\text{(890)π}$ and $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^1\text{→ Δπ}$ decay modes. In this particular final state the double fragmentation system is produced with a cross section of the order of a few microbarns. Our data are consistent with the factorizable pomeron exchange model of double diffractive dissociation.     

Formation of Xe12 by collision pair absorption at 158 nm

Pair absorption from colliding Xe atoms of the molecular fluorine laser radiation is reported. The absorption coefficient for this process at 300 K was found to be α = (4.32 ± 0.1) × 10^-9Torr^-2cm^-1. Fluorescence at 172 nm originating predominantly from the ${}^1\text{Σ}{}^{\mathrm{+}}{}_{\mathrm{u}}$ state of Xe¹₂ indicates that by this mechanism the Xe dimer laser can be pumped optically.     

Dye laser site selection spectroscopy on U6+ luminescent molecular centers in LiF-U3O8 crystals

The polarized excitation and emission spectra of the U⁶⁺ molecular centers giving the most intense emission lines at 18 940 cm^?1 and 19 285 cm^?1 are presented and analyzed in detáil. From the polarization experiments, it is shown that the symmetry of the centers is C_4v and that the symmetries of the observed electronic states are Γ₂, Γ₁ and Γ₅. Finally, an electronic model is proposed which associates the emission and excitation lines of the U⁶⁺ centers in the visible region to transitions between the fundamental state $\text{Γ}{}_1\text{(6p}{}^6\text{,}{}^1\text{S)}$ and the states of the excited configuration $\text{6p}{}^5\text{(}{}^2\text{P}\text{3}\text{2}\text{) 7s}$.     

Spectral and temperature characteristics of Cs2Na(Er,Yb, Y)Cl6 upconverters

Spectral luminescence characteristics of the Cs₂Na(Er, Yb, Y)Cl₆ type upconverter have been measured in the range 300–650 K. A nearly sixfold decrease of the emission intensity of an upconverter was observed in the green area. This emission corresponds to two luminescence transition of Er³⁺ ions: ${}^2\text{H}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$ and ${}^4\text{S}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$. A mechanism of the luminescence intensity decrease has been proposed, in which deexcitation of the ${}^4\text{S}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ level to the ${}^4\text{I}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ level is caused by a neighbouring Er³⁺ ion being excited to the ${}^4\text{I}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ level.