The fragmentation of negative ions of fullerene C60 trifluoromethyl derivatives

The formation and decay of gas-phase negative ions of trifluoromethylated fullerenes C₆₀(CF₃) _n (n = 2–10) were studied. The resonance electron capture mass spectra were measured to find that the main fragmentation channel of negative ions was the detachment of trifluoromethyl groups. The degree of fragmentation directly depended on the energy of electrons and reached the complete splitting off of all the CF₃ addends with the formation of C₆₀⁻ ions. The observed metastable ion signals were analyzed to determine the scheme of sequential fragmentation of negative ions.     

Slow decay of negative molecular fluorofullerene ions in the electron autodetachment process

The mean lifetimes of negative molecular ions of C₆₀ fullerene and its fluoroderivatives C₆₀F₁₈ and C₆₀F₃₆ with respect to the autodetachment of electrons have been measured as functions of the ionizing electron energy by the method of mass spectrometry of electron resonance capture. The lifetimes of negative ions in the compounds under investigation are within the one-second range, and an increase in the number of addends leads to an increase in the lifetimes of negative ions by 1.5–2.5 orders of magnitude.     

On the delay mechanism of Cl<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> diatomic anion dissociation up to the microsecond timescale

The dissociative capture of slow electrons by tetrachlorethylene (C₂Cl₄) has been investigated by resonant electron capture negative ion mass spectrometry. Metastable ions with fractional mass numbers 7.5, 17.5, and 19 corresponding to the C₂Cl₄⁻ → Cl⁻ + C₂Cl₃ and Cl₂⁻ → Cl⁻ + Cl decays occurring at the microsecond timescale have been detected. It has been revealed that Cl₂⁻ anions, which are fragment ions, can dissociate at the microsecond timescale, which is very surprising for a system with one internal degree of freedom. This process is assumingly attributed to the rotational excitation of Cl₂⁻ anions. Thus, the experimental estimate of the time of rovibronic relaxation in the Cl₂⁻ anion has been obtained.     

Enhancement of minority carrier lifetime in GaAs1? x P x ( x =0.4; 0.65) by nitrogen implantation

Minority carrier lifetimes in nitrogen implanted GaAs_1-x P _x (x=0.4; 0.65) were measured at 77K by an optical phase shift method as a function of nitrogen dose and annealing temperature in order to investigate the dependence of the lifetime on the concentration of nitrogen isoelectronic traps. A large increase in the lifetime was observed after nitrogen implantation followed by annealing at and above 800°C. The maximum lifetimes were 22ns for GaAs_0.35P_0.65 and 6.7 ns for GaAs_0.6P_0.4. They were obtained by implantation to a dose of 5×10¹³ cm⁻² in GaAs_0.35P_0.65 and 10¹³ cm⁻² in GaAs_0.6P_0.4. The lifetime after nitrogen implantation followed by annealing was longer by a factor of 6–7 than that of the unimplanted sample.     

The metal-semiconductor transition monitored by excited state lifetimes of Al4O m − clusters

The lifetimes of electronically excited states of Al₄O _m ⁻ clusters are measured for m=1,3,4,5, and 6 using time-resolved photoelectron spectroscopy. With increasing number of oxygen atoms the lifetimes increase. This can be explained qualitatively by a metal-semiconductor transition occurring between the metal-like Al₄ ⁻ cluster and the fully oxidized semiconductor-like Al₄O₆ ⁻ cluster. Long lifetimes of electron-hole excitations are characteristic for semiconductors, while in metals the strong interaction between the delocalized electrons causes short lifetimes.     

Reactions and anion desorption induced by low-energy electron exposure of condensed acetonitrile

Thermal desorption spectrometry (TDS) and electron stimulated desorption (ESD) are employed to investigate mechanisms responsible for the formation of C₂H₆ in electron irradiated multilayer films of acetonitrile (CH₃CN) at 30 K. Using a high sensitivity time-of-flight mass spectrometer, we observe the ESD of anionic fragments H⁻, CH₂ ⁻, CH₃ ⁻ and CN⁻. Desorption occurs following dissociative electron attachment (DEA) via several negative ion resonances in the 6 to 14 eV energy range and correlates well with a “resonant” structure seen in the TDS yield of C₂H₆ (i.e., at mass 30 amu). It is proposed that C₂H₆ is formed by the reactions of CH₃ radicals generated following DEA to CH₃CN which also yields CN⁻. Between 2 and 5 eV, a second resonant feature is seen in the C₂H₆ signal. While DEA is observed in the gas phase at these energies, no anion desorption occurs since anionic fragments likely have insufficient kinetic energy to desorb. Since the CH₂ ⁻ ion has not been observed in gas-phase measurements, we propose that it is formed, along with HCN (that is detected in TDS) when dissociation into CH₃ ⁻ and CN is hindered by adjacent molecules.     

Spectroscopic properties of Nd<Superscript>3+</Superscript>:CaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> crystal

The absorption spectra, fluorescence spectrum and fluorescence decay curve of Nd³⁺ ions in CaNb₂O₆ crystal were measured at room temperature. The peak absorption cross section was calculated to be 6.202×10⁻²⁰ cm² with a broad FWHM of 7 nm at 808 nm for E//a light polarization. The spectroscopic parameters of Nd³⁺ ions in CaNb₂O₆ crystal have been investigated based on Judd-Ofelt theory. The parameters of the line strengths Ω _t are Ω ₂=5.321×10⁻²⁰ cm²,Ω ₄=1.734×10⁻²⁰ cm²,Ω ₆=2.889×10⁻²⁰ cm². The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 167 μs, 152 μs and 91%, respectively. The fluorescence branch ratios are calculated to be β ₁=36.03%,β ₂=52.29%,β ₃=11.15%,β ₄=0.533%. The emission cross section at 1062 nm is 9.87×10⁻²⁰ cm².     

Total rates of nuclear capture of negative muons in the isotopes 132Xe and 40Ar

The lifetimes of a negative muon in the isotopes ¹³²Xe and ⁴⁰Ar in the solid phase are measured. The lifetime of μ ⁻ in the 1s state of the isotope ¹³²Xe is τ(¹³²Xe)=101.7±1.7 ns, which corresponds to a total nuclear capture rate Λ_c(¹³²Xe)=9.4±0.2 μs⁻¹. The lifetime of μ ⁻ in the isotope ⁴⁰Ar, viz., τ (⁴⁰Ar)=568±6 ns, corresponding to a capture rate Λ_c(⁴⁰Ar)=1.31±0.01 μs⁻¹, is obtained to several times better accuracy as compared to previously published results. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 181–183 (10 February 1999)     

Optical spectra and excited state relaxation dynamics of Sm<Superscript>3+</Superscript> in Gd<Subscript>2</Subscript>SiO<Subscript>5</Subscript> single crystal

Single crystals of gadolinium orthosilicate Gd₂SiO₅ containing 0.5 at% and 5 at% of Sm³⁺ were grown by the Czochralski method. Optical absorption spectra, luminescence spectra and luminescence decay curves were recorded for these systems at 10 K and at room temperature. Comparison of optical spectra recorded in polarized light revealed that the anisotropy of this optically biaxial host affects the intensity distribution within absorption and emission bands related to transitions between multiplets rather than the overall band intensity. It has been found that among four bands of luminescence related to the ⁴G_5/2→⁶H_J (J=5/2–11/2) transitions of Sm³⁺ in the visible and near infrared region the ⁴G_5/2 →⁶H_7/2 one has the highest intensity with a peak emission cross section of 3.54×10⁻²¹ cm² at 601 nm for light polarized parallel to the crystallographic axis c of the crystal. The luminescence decay curve recorded for Gd₂SiO₅:0.5 at% Sm³⁺ follows a single exponential time dependence with a lifetime 1.74 ms, in good agreement with the ⁴G_5/2 radiative lifetime τ _rad=1.78 ms calculated in the framework of Judd-Ofelt theory. Considerably faster and non-exponential luminescence decay recorded for Gd₂SiO₅:5 at% Sm³⁺ sample was fitted to that predicted by the Inokuti-Hirayama theory yielding the microparameter of Sm³⁺–Sm³⁺ energy transfer C _da=1.264×10⁻⁵² cm⁶×s⁻¹.     

Decay rate measurements of upper laser level in He-Cd+ laser

The decay rate of² D _5/2 level of Cd II has been measured by the magnetic-field power-dip method. The decay rate at the zero-pressure limit is found to be 2.4·10⁶s⁻¹. The calculated collision cross section for excited Cd ions with He atoms equals 0.91·10⁻¹⁵ cm². This work was supported by the Institute of Quantum Electronics. WAT Warszawa, within the project 06.2.3.     

Development of a New Experimental Method for Studies of Muon Capture in Hydrogen

A new experiment is under preparation with the aim to improve considerably the present knowledge of the rate Λ _s , which should be measured on a level of 1% or better, for the basic electroweak capture reaction of a negative muon on the free proton μp _1s → n + ν_μ. The capture rate will be determined by measuring the lifetime of μ⁻ stopped in ultra pure hydrogen at 10 bar pressure and comparing it with the lifetime of the unbound μ⁺. A new experimental method was developed for this project which should allow measuring the μ⁻ lifetime with at least 10 ppm precision. The basic element of the detector is operating in the hydrogen gas time projection chamber (TPC) surrounded by multi-wire proportional chambers (MWPCs) and scintillator counters. The arrival times and trajectories of the incoming muons and the outgoing decay electrons are measured with this device providing effective suppression of background. Using the TPC as an active target, we can monitor on-line the protium contamination by impurities with a sensitivity better than 10⁻⁸. This can be done by detecting the charged products of the muon capture reaction on these impurities. It was demonstrated that the TPC and MWPCs can operate in pure hydrogen under 10 bar pressure providing gas gain up to 10 000. This revised version was published online in August 2006 with corrections to the Cover Date.     

Infrared luminescence of erbium-doped sodium lead germanate glass

The infrared optical properties of Er³⁺ ions are reported for 60GeO₂–20PbO–20Na₂O glass for two Er₂O₃ concentrations. From the optical absorption spectra, the Judd–Ofelt (J–O) parameters have been obtained and have been used to calculate radiative lifetimes and stimulated emission cross sections. A narrow emission band peaked at 1536 nm with exponential decay for both Er concentrations is observed. The measured lifetime decreases for increasing Er concentration, its value being very close, in the case of the lowest doping level, to the radiative lifetime calculated from J–O analysis. This, together with the relatively high emission cross section makes this glass suitable for laser applications.     

Tm-Ho and Tm-Tb energy transfer in tellurite glass

In Tm³⁺-Ho³⁺- and Tm³⁺-Tb³⁺-doped tellurite glasses, the IR fluorescence spectra and the lifetimes of the upper ³H₄ and lower ³F₄ lasing levels for 1.47 μm of Tm³⁺ were measured. The non-exponential decay is fitted using the Inokuti-Hirayama equation. The energy-transfer parameter C_DA, critical ion distance R₀, lifetime and non-radiative energy-transfer efficiency η between donor and acceptor ions are compared. The quenching mechanism has been explained. Both Ho³⁺ and Tb³⁺ ions reduce the lifetimes of the upper and lower lasing levels, with Tb³⁺ ions proving more efficient than the effects observed for Ho³⁺ ions. The optimised Tb₂O₃ concentration is about 1.0-1.5 wt%, which produced effective inversion and could be used for laser and amplifier applications.     

The Studies of Enhanced Fluorescence in the Two Novel Ternary Rare-Earth Complex Systems

Two novel ternary rare-earth complexes SmL₅·L^’·(ClO₄)₂·7H₂O and EuL₅·L^’·(ClO₄)₂·6H₂O (the first ligand L = C₆H₅COCH₂SOCH₂COC₆H₅, the second ligand L^’ = C₆H₄OHCOO⁻) were synthesized and characterized by element analysis, molar conductivity, coordination titration analysis, IR, TG-DSC, ¹HNMR and UV spectra. The detailed luminescence studies on the rare-earth complexes showed that the ternary rare-earth complexes presented stronger fluorescence intensities, longer lifetimes, and higher fluorescence quantum efficiencies than the binary rare-earth materials. After the introduction of the second ligand salicylic acid group, the relative emission intensities and fluorescence lifetimes of the ternary complexes LnL₅·L^’·(ClO₄)₂·nH₂O (Ln = Sm, Eu; n = 7, 6) enhanced more obviously than the binary complexes LnL₅·(ClO₄)₃·2H₂O. This indicated that the presence of both organic ligand bis(benzoylmethyl) sulfoxide and the second ligand salicylic acid could sensitize fluorescence intensities of rare-earth ions, and the introduction of salicylic acid group was a benefit for the fluorescence properties of the ternary rare-earth complexes. The fluorescence spectra, fluorescence lifetime and phosphorescence spectra were also discussed.     

O<Subscript>2</Subscript> photodesorption from AuO<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and Au<Subscript>2</Subscript>O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>

Using time-resolved photoelectron spectroscopy, the decay channels of AuO₂⁻ and Au₂O₂⁻ following photoexcitation with 3.1-eV photons have been studied. For AuO₂⁻, a state with a rather long lifetime of 30 ps has been identified. Its decay path could not be determined but photodesorption can be excluded. For Au₂O₂⁻, the spectra indicate O₂ desorption after 3.1-eV photoexcitation on a time scale of 1 ps. While comparing these results on Au _n O₂⁻ with analogous data on Ag _n O₂⁻ clusters, a discernible pattern emerges: for dissociatively bound O₂(AuO₂⁻, Ag₃O₂⁻), there are long-living excited states which do not decay by oxygen desorption, while for molecular chemisorption (Au₂O₂⁻, Ag₂O₂⁻, Ag₄O₂⁻, Ag₈O₂⁻), the 3.1-eV photoexcitation triggers fast O₂ desorption with a high quantum yield.     

Determination of temperature in a plasma jet emanating from a plasma torch with sectioned inter-electrode insert from the molecular emission spectrum of nitrogen

Results of application of a method for measuring the distribution of temperature in a nitrogen plasma jet emanating from a dc plasma torch with sectioned inter-electrode insert from the relative intensities of the molecular emission bands of nitrogen in the N₂ ⁺(B²Σ_u ⁺ − X²Σ_g ⁺) first negative and N₂(C³Π_u ⁺ − B³Π_g ⁺) second positive systems are reported. The emission spectra were registered using a small-size spectrometer with medium-range spectral resolution enabling a contour analysis of ro-vibrational bands in molecular emission spectra. The obtained distribution of temperature was compared with the distribution that was determined from the emission lines due to copper atoms and with the mean-mass plasma temperature of the air plasma jet.     

Fluorescence of jet-cooled naphthalene: Emission spectra, lifetimes and quantum yields

Fluorescence spectra of naphthalene, C₁₀H₈, were obtained in the laboratory under conditions which provide an appropriate simulation of the cometary conditions: super-cooled gas phase molecules in a collision-free environment. Five spectra were recorded, the excitation energies ranging from 1422 to 5293 cm⁻¹ above the first electronic state S₁ at 32 020 cm⁻¹. A comparison with previous jet-cooled naphthalene fluorescence spectra obtained by Beck et al. [1] and Hermine [2] shows that the former results are not consistent with the present ones. Spectra obtained by Beck et al. show weaker intensities at greater wavelengths compared to those obtained by Hermine and ourselves. We also measured the fluorescence lifetimes by recording the fluorescence decay as a function of time after the excitation of the molecules by monochromatic lasers and deduced the fluorescence quantum yields. A synthetic emission spectrum under solar irradiation is obtained for astrophysical implications.     

Experimental study of the <Emphasis Type="Italic">πh</Emphasis><Subscript>11/2</Subscript> band in <Superscript>113</Superscript>Sb

In the present work, the excited states of ¹¹³Sb were populated in the ¹⁰⁰Mo(²⁰Ne, p6n) reaction at a beam energy of 136 MeV. States only up to 59/2⁻ were observed in the ΔJ = 2 band. Mean lifetimes for the five states (from 4460 to 7998 keV) were measured for the first time using Doppler shift attenuation method. An upper limit of the lifetime (0.14 ps) was estimated for the 9061 keV, 47/2⁻ state. The B(E2) values, derived from the present lifetime results, correspond to a large quadrupole deformation of β ₂ = 0.32. The observed reduction in the experimental B(E2) values for the 918.4 keV (spin 39/2⁻ → 35/2⁻) and 985 keV (spin 43/2⁻ → 39/2⁻) transitions may be interpreted as due to the proton alignement in the g _7/2 orbital. The dynamic moment of inertia was observed to be about half of the rigid body value at the highest observed frequency.     

A Molecular Thermometer Based on the Delayed Fluorescence of C70 Dispersed in a Polystyrene Film

A new optical molecular thermometer, based on the thermally activated delayed fluorescence of C₇₀ dispersed in a polystyrene film, was developed. In the presence of oxygen, the fluorescence intensity of the C₇₀ film is essentially temperature independent in a wide range. In the absence of oxygen, however, the fluorescence intensity markedly increases with temperature. At room temperature (25°C), and after degassing the sample, the fluorescence intensity of C₇₀ increases 22 times, while at 100°C the fluorescence intensity is increased by 70 times. With our system, the very weak fluorescence of C₇₀ (Φ_F ≅ 5 × 10⁻⁴, in toluene) can be increased up to 91 times (up to an estimated maximum value Φ_F = 0.046). The estimate value of the singlet-triplet gap (29 kJ mol⁻¹) and the fluorescence lifetime (0.63 ns) of the C₇₀ in film are in agreement with the values reported in the literature for C₇₀ in solution. The values of the phosphorescence lifetime at room temperature (23 ms) and the quantum yield of triplet formation (0.989) were also determined. The system is completely reversible with respect to heating-cooling cycles.     

Interaction of chloride ions with water clusters absorbing ozone: A computer experiment

The molecular dynamics method is used to investigate the interaction of two, four, and six chloride ions with (H₂O)₅₀, clusters absorbing six ozone molecules. Chloride ions moving toward the cluster penetrate into it. The presence of ozone increases the residence time of Cl⁻ ions in the cluster. The duration of the perturbation increases with the number of Cl⁻ ions surrounding the 6O₃ + (H₂O)₅₀ system. The interaction with Cl⁻ ions enhances the positional disorder of the molecules in the system and enhances the intensity of absorption and emission of infrared radiation. These changes, however, are not monotonic function of the number of ions perturbing the system. As a result of the interaction with Cl⁻ ions, the integrated intensity of the Raman scattering on the (O₃)₆(H₂O)₅₀ cluster in the frequency range 0 ≤ ω ≤ 1100 cm⁻¹ is significantly lower and the number of peaks in the spectrum is smaller.