Kinetic investigation of electronic energy transfer processes following the pulsed dye-laser generation of excited atomic barium, Ba[6s6p(P1)], in the presence of atomic strontium

The collisional behaviour of Ba[6s5d(³D_J)], 1.151 eV above the 6s²(¹S₀) electronic ground state, in the presence of atomic strontium, has been investigated in the ‘long-time domain' (ca. 100 μs–1 ms) following the pulsed dye-laser excitation of barium vapour at elevated temperature at λ = 553.5 nm (Ba[6s6p(¹P₁)] ← Ba[6s²(¹S₀)]. Ba(³D_J) is subsequently produced from the short-lived ¹P₁ state (τ_e = 8.37 ± 0.38 ns) by a number of radiative and collisional processes. It may then be monitored in the ‘long-time domain' by atomic spectroscopic marker methods involving either collisional activation of Ba(³D_J) by Ba(¹S₀) and He buffer gas to yield Ba[6s6p(³P_J)] with subsequent emission from the ³P₁ state (τ_e = 1.2 ± 0.1 μs): Ba[6s6p(³P₁)] → Ba[6s²(¹S₀)] + hv (λ = 791.1 nm). Alternatively, emission from Ba(¹P₁) may be monitored at long times following the generation of this short-lived state by energy pooling following self-annihilation of Ba(³D_J) + Ba(³D_J) from Ba[6s6p(¹P₁)] → Ba[6s²(¹S₀)] + hv (λ = 553.5 nm). The generation of Ba(³D_J) in the presence of atomic strontium yields emission in the long-time domain from Sr[5s5p(³P₁)] (τ_e = 19.6 μs): Sr[5s5p(³P₁)] → Sr[5s²(¹S₀)]  + hv (λ = 689.3 nm). Whilst the decay profiles at short times are complex in form, at long times all these atomic profiles show first-order kinetic removal with the decay coefficients for λ = 791.1 nm, 689.3 nm and 553.5 nm emissions in the ratio 1 : 2 : 2, consistent with overall third-order activation of the form: Ba(³D_J) + Ba(³D_J) + Sr(¹S₀) → Sr(³P_J) + 2Ba(¹S₀). The mechanism is modelled in detail, including measurement of integrated emission intensities, yielding kinetic data for fundamental collisional processes. The overall rate constant for the third-order collisional activation of Sr[5s5p(³P_J])from 2Ba[6s5d(³D_J)] + Sr[5s²(¹S₀)] takes the upper limit of 5.8 × 10⁻²⁷ cm⁶ atom⁻² s⁻¹ (T = 900 K). The rate constant for the two body collisional quenching of Ba[6s5d(³D_J)] by ground state atomic strontium, Sr[5s²(¹S₀)], is found to be (2.0 ± 0.1) × 10⁻¹² cm³ atom⁻¹ s⁻¹ (T = 900 K).     

Collisional quenching of electronically excited germanium atoms, Ge[4p(S0)], by small molecules investigated by time-resolved atomic resonance absorption spectroscopy

The collisional quenching of electronically excited germanium atoms, Ge[4p²(¹S₀)], 2.029 eV above the 4p²(³P₀) ground state, has been investigated by time-resolved atomic resonance absorption spectroscopy in the ultraviolet at λ = 274.04 nm [4d(¹P₁⁰) ← 4p²(¹S₀)]. In contrast to previous investigations using the ‘single-shot mode’ at high energy, Ge(¹S₀) has been generated by the repetitive pulsed irradiation of Ge(CH₃)₄ in the presence of excess helium gas and added gases in a slow flow system, kinetically equivalent to a static system. This technique was originally developed for the study of Ge[4p²(¹D₂)] which had eluded direct quantitative kinetic study until recently. Absolute second-order rate constants obtained using signal averaging techniques from data capture of total digitised atomic decay profiles are reported for the removal of Ge(¹S₀) with the following gases (k_R in cm³ molecule⁻¹ s⁻¹, 300 K): Xe, 7.1 ± 0.4 × 10⁻¹³; N₂, 4.7 ± 0.6 × 10⁻¹²; O₂, 3.6 ± 0.9 × 10⁻¹¹; NO, 1.5 ± 0.3 × 10⁻¹¹; CO, 3.4 ± 0.5 × 10⁻¹²; N₂O, 4.5 ± 0.5 × 10⁻¹²; CO₂, 1.1 ± 0.3 × 10⁻¹¹; CH₄, 1.7 ± 0.2 × 10⁻¹¹; CF₄, 4.8 ± 0.3 × 10⁻¹²; SF₆, 9.5 ± 1.0 × 10⁻¹³; C₂H₄, 3.3 ± 0.1 × 10⁻¹⁰; C₂H₂, 2.9 ± 0.2 × 10⁻¹⁰; Ge(CH₃)₄, 5.4 ± 0.2 × 10⁻¹¹. The results are compared with previous data for Ge(¹S₀) derived in the single-shot mode where there is general agreement though with some exceptions which are discussed. The present data are also compared with analogous quenching rate data for the collisional removal of the lower lying Ge[4p²(¹D₂)] state (0.883 eV), also characterized by signal averaging methods similar to that described here.     

Two-photon laser optogalvanic studies of the 6snf F4 Rydberg states of mercury by RF discharge

We present new experimental data on the energies and quantum defects of the highly excited states in mercury using the laser optogalvanic detection technique in conjunction with a RF discharge cell. The 6snp ³P₂ (12 ≤ n ≤ 25) and 6snf ³F₄ (9 ≤ n ≤ 52) Rydberg series have been observed via two photon excitation from the 6s6p ³P₂ intermediate state, which is collisionally populated in the RF discharge. Three lines corresponding to transitions from the 6s6p ³P₀ metastable state to 6s8p ³P_0,2 and 6s5f ³F₂ states are also located. The 6snf ³F₄ Rydberg series to such high n-values are reported for the first time.     

Cl (Pj)_ fine structure quantum yields from UV dissociation of PCl3, CCl4, CHCl3 and Cl2 in a supersonic jet

Jet-cooled phosphorus trichloride, carbon tetrachloride, chloroform and molecular chlorine are photodissociated in the UV wavelength range 235–238 nm. Chlorine atom photofragments Cl (²P_3/2) and Cl* (²P_1/2) are detected via resonance-enhanced (2+1) ionization throughout the 232–238 nm wavelength region. The relative Cl* yields, φ*=[Cl*]/([Cl]+[Cl*]), are measured for both ³⁵Cl and ³⁷Cl isotopes using the two-photon atomic transitions at 235.3 nm for Cl and 237.8 nm for Cl*. Preliminary results indicate that the Cl* yields are different for the two isotopes for some of the precursors. In addition, we obtained the two-photon oscillator strength of the Cl transition at 237.7 nm relative to the Cl* transition at 237.8 nm. The advantage of using the two-photon Cl transition at 237.7 nm for quantum yield measurements is discussed.     

Yb ion as a sensitizer for the upconversion luminescence in nanocrystalline Gd3Ga5O12:Ho

The effect of Yb³⁺ co-doping on the upconversion luminescence in nanocrystalline Gd₃Ga₅O₁₂:Ho³⁺ was examined. Strong and efficient NIR to green anti-Stokes luminescence was noted in nanocrystalline Gd₃Ga₅O₁₂:Ho³⁺, Yb³⁺ after excitation into the ²F_5/2 level of Yb³⁺ with 978 nm radiation. Weaker blue, red and NIR anti-Stokes luminescence was also observed after 978 nm excitation. An enhancement of the red ⁵F₅ → ⁵I₈ luminescence was observed in the anti-Stokes spectrum compared to the Stokes emission spectrum. This enhancement was attributed to two distinct energy transfer upconversion (ETU) mechanisms which preferentially populate the (⁵F₄, ⁵S₂) and ⁵F₅ levels.     

Reaction dynamics of the Ca(D2, PJ) + CH3I → CaI + CH3 system: chemiluminescence, energy disposal and product polarization

The Ca(¹D₂, ³P_J) + CH₃ → CaI(A,B) + CH₃ reactions system has been studied by measuring its chemiluminescence under beam-gas conditions. Absolute values of the state-to-state reaction cross-sections were determined at low collision energy . In addition, the electronic branching ratio and product energy disposal have been determined for each metastable reaction. The major changed observed in the chemiluminescence when comparing the Ca(¹D₂) reaction versus that of Ca(³P_J) is the total yield associated with the former reaction. To the best of our spectral resolution neither the electronic branching ratio e.g. CaI(A)/CaI(B) nor the internal CaI energy disposal change significantly as the metastable Ca(¹D₂)/Ca(³P_J) ratio is varied. In spite of the fact that the Ca(³P_J) reaction is less exoergic, the CaI product appears with a higher fraction of internal energy than that of Ca(¹D₂) reaction. Thus, the fraction of the total energy appearing in CaI internal energy amounts to 57.5% in the Ca(³P_J) reaction while it is 19.3% only for the Ca(¹D₂) reaction. This difference is discussed in the light of a distinct mechanism associated with the attack of the excited Ca atom into the C---I bond. No significant chemiluminescence yield was found for the energetically open CaCH^*₃ channels.

The product chemiluminescence polarization was also measured as a function of the metastable concentration. A significant degree of polarization was found depending upon the specific electronic excitation. The analysis of the polarization emission associated to the parallel CaI(X ²Σ⁺ ← B ²Σ⁺) emission led into a strong polarization of the product rotational angular momentum. The comparison of the product rotational alignment for the kinematically identical Ca(¹D₂, ³P_J, ¹P₁) + CH₃ → CaI^* (B₂Σ⁺) + CH₃ reaction system showed that the CaI rotational polarization diminishes in the ³P_J → ¹D₂ → ¹P₁ sequence, e.g. as the reaction exothermicity increases. In addition the degree of polarization associated with other emission bands as for example CaI(X ²Σ⁺ ← A ²Π_1/2) indicates the presence of a parallel transition which was been interpreted as mixing of Hund's case (a) and (c) appropriate for this heavy CaI diatom produced with a high rotational excitation.     

Estimation of the emission temperature of an electrodeless discharge lamp and determination of the oscillator strength for the I(P3/2) 183.038 nm resonance transition

The 183.038 nm resonance absorption transition of I(²P_3/2) has been studied using a flash photolysis set-up for gas-phase chemistry and a radio frequency powered electrodeless discharge lamp filled with iodine. The dependence of self-absorption and self-reversal on iodine partial pressure in the discharge volume was measured. The optimum iodine partial pressure, with self-absorption minimized and acceptable intensity, is determined to be approximately 2.5×10⁻³ mbar. A method is described to estimate the temperature of the emitting atoms using direct measurements of relative absorption at different absorber concentrations. This yields an emission temperature of 923±50 K. Using this temperature, the oscillator strength for the I(²P_3/2) transition at 183.038 nm is determined to be f=(3.87±0.57)×10⁻³, corresponding to an absorption cross-section at the center of the line of σ=(5.42±0.8)×10⁻¹⁴ cm² atom⁻¹_. This shows a difference from one of two earlier measurements, but is close to the other. The remaining difference from the latter measurement is probably due to tendencies of opposite biases inherent to the experiments.     

Comparison of zinc and cadmium plasma parameters produced by laser-ablation

We report the measurement of the zinc and cadmium plasma parameters produced by the fundamental, second, and third harmonics of the neodymium-doped yttrium aluminium garnet laser. The excitation temperature has been determined from the Boltzmann plot method, whereas the electron number density is estimated from the Stark broadened profile of several spectral lines. The temporal evolution of the plasma has also been investigated. Besides, we present experimental relative transition probabilities of the Zn (4s5s ³S₁ → 4s4p ³P_0,1,2) and Cd (5s6s ³S₁ → 5s5p ³P_0,1,2) triplets and compare our data with that listed in the National Institute of Standards and Technology database. The experiments have been performed in air but also in He, Ne and Ar atmosphere to study the effects of ambient gas environment on the emission intensity of the atomic and ionic lines and on the plasma parameters.     

Vibrational population inversion in CS(A) through the dissociative excitation of CS2 by Ar(P2)

The CS(A ¹Π → X ¹Σ⁺) emission spectra resulting from the energy transfer reaction of Ar(³P₂) + CS₂ under single collision condition have been obtained. The relative vibrational populations of the nascent product CS(A ¹Π, υ′) have been determined by means of spectral simulation. A population inversion is found at υ′ = 1. The population data are approximately represented by a distribution predicted from the impulsive half collision model. The dynamics and energetics of CS(A) formation has been discussed in detail.     

1.54 and 1.75 μm infrared luminescence of Y2O3:Er

A new 1.75 μm infrared emission transition of Y₂O₃:Er³⁺ is assigned to the ⁴S_3/2 → ⁴I_9/2 transition of Er³⁺ ions situated at the C₂ sites of cubic RE₂O₃ (RE = Y, Gd, Lu). The intensities of features in the 1.54 μm ⁴I_15/2–⁴I_13/2 absorption transition due to Er³⁺ at S₆ and C₂ sites are consistent with the site occupation ratio and the relative magnetic dipole–electric dipole intensity contributions of Er³⁺ at the different sites. The 1.54 μm emission lines are predominantly from Er³⁺ ions at C₂ sites. The different behaviours of the emission intensities 1.75 and 1.54 μm groups with change in Er³⁺ dopant ion concentration, preparation technique, Yb³⁺ co-doping, temperature change and different excitation line are rationalized.     

Preparation and Luminescence Behavior of CaSiO3：Eu^3＋（Bi^3＋）

CaSiO3：Eu0.08^3＋Bi0.002^3＋ with a monoclinic perovskite structure was synthesized by using sol-gel method, and its luminescence characteristics were investigated. From the excitation spectrum, it can be seen that the main peaks located at 238,396,415,437 and 359 nm correspond to the charge-transfer band of Eu^3＋-O^2- , the absorption transitions of ^7F0.1→^3L6, ^7F0→^5D3, ^7F1→^5D3 of Eu^3＋ ions, and ^3P1→^1S0 of Bi^3＋ ions, respectively. When the samples were excited with a light of wavelength 359 or 395 nm, it can be seen from the emission spectrum that the electronic dipole transition located at 609 nm corresponding to ^5D0→^7F2 of Eu^3＋ ions was stronger than the magnetic dipole transition located at 587 nm corresponding to ^5D0→^7F1 of Eu^3＋ ions, which shows that more Eu^3＋ ions were located in nonreversion center lattices. The energy transfer from Bi^3＋ ions to Eu^3＋ ions in the phosphor was also discussed. The results show that Eu^3＋ ions could be well sensitized by ^3＋ions, and the energy-transfer pattern between Bi^3＋ ions and Eu^3＋ ions was resonance energy transfer.     

Kinetic processes of Hg6s6p(P1) in xenon

The principal route for decay of Hg 6s6p(³P₁) in xenon is shown to be bimolecular deactivation to the mercury ground state, with rate coefficient 9.1 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹; relaxation to the ³P₀ state plays a negligible role. The equilibrium constant of the reaction Hg(³P₁) + Xe HgXe(A ³O⁺), has been recorded as 1.73 × 10⁻²⁰ cm³ molecule⁻¹ at 293 K.     

La_(2.4)Mo_(1.6)O_8∶Yb~(3+),Er~(3+)材料的制备及其上转换发光性质

采用高温固相法制备了La_(2.4)Mo_(1.6)O_8∶Yb~(3+),Er~(3+)荧光粉。通过X射线衍射(XRD)和上转换发射光谱对样品进行了相结构和发光性质表征。XRD实验结果表明:合成的样品为面心立方萤石结构(Fm-3m)的La_(2.4)Mo_(1.6)O_8相。在980 nm红外光激发下,La_(2.4)Mo_(1.6)O_8∶Yb~(3+),Er~(3+)荧光粉发出分别来自Er~(3+)离子的~2H1_(1/2)→~4I_(15/2)、~4S_(3/2)→~4I_(15/2)跃迁的绿光(主峰为548和529 nm)和~4F_(9/2)→~4I_(15/2)跃迁的红光(主峰为670 nm)。进一步地,对样品中可能的上转换发光机制进行了讨论。     

Luminescent properties of carbon-rich starburst gold(I) acetylide complexes. Crystal structure of [TEE][Au(PCy3)]4 ([TEE]H4=tetraethynylethene)

Two carbon-rich starburst gold(I) acetylide complexes [TEE][Au(PCy₃)]₄ (3, [TEE]H₄=tetraethynylethene) and [TEB][Au(PCy₃)]₃ (6, [TEB]H₃=1,3,5-triethynylbenzene) were prepared and their UV–vis absorption, emission and excitation spectra have been recorded. In fluid CH₂Cl₂ solutions, 3 exhibits prompt ¹(ππ*) fluorescence with λ_0–0 and λ_max at 413 and 428 nm, respectively, while 6 displays ³(ππ*) phosphorescence with λ_0–0 and λ_max at 446 and 479 nm, respectively. The crystal structure of 3·CH₂Cl₂ has been determined.     

193 nm Laser dissociation of CS2: prompt emission from CS and internal energy distribution of CS(XΣ)

Single and multiple photon processes are identified in the 193 nm excimer laser photolysis of CS₂. CS(X¹Σ⁺, υ = 1 to 5, J = 5 to 45) is observed by dye laser induced fluorescence of the A¹Π ↔ ; X¹Σ⁺ transition, following the single photon 193 nm photolysis of CS₂. Multiple photon 193 nm generation of CS fragment emission from 620 to 170 nm is also reported. A partial assignment of the emission spectrum identifies fluorescence from the CS A′¹Σ⁺ and A¹Π states.     

A study of the B2 excited state geometries of the metal-metal quadruply bonded compounds Mo2X4(PMe3)4 (X = Cl, Br or I)

The excited state geometries of the metal-metal quadruply bonded compounds Mo₂X₄(PMe₃)₄ (X = Cl, Br or I) have been studied by means of resonance Raman and absorption spectroscopy. A fit of the parameters of a simple theoretical model to the experimental data indicates that the metal-metal bond increases some 10 pm on excitation to the ¹B₂ (δδ^*) state, whereas other geometric changes are small. Furthermore, the phenomenological lifetime factor of the excited state, Γ, is found to be dependent on the vibrational quantum number, ν, of this state.     

Evidence for two light-induced metastable states in Cl3[Ru(NH3)5NO]H2O

Differential Scanning Calorimetry measurements on irradiated Cl₃[Ru(NH₃)₅NO]H₂O reveal the existence of two light-induced long-lived metastable states SI, SII. Irradiation with light in the spectral range 400–500 nm leads to the excitation of SI. For the first time we report experimental evidence for the state SII in this compound, which can be excited by transferring SI into SII with irradiation of light in the spectral range 1000–1200 nm. The excitation and transfer of the metastable states is described and the exponential decays are evaluated according to Arrhenius' law yielding activation energies of E_A(SI)=0.73(3) eV, E_A(SII)=0.66(3) eV and frequency factors of Z(SI)=1 × 10¹² s⁻¹, Z(SII) = 5 × 10¹² s⁻¹.     

Landé factor measurement for the Te2 electronic ground state

Non-linear ground-state quantum beat resonance under harmonically modulated excitation has been studied for a single rovibrational level of a diatomic molecule. Excitation of tellurium dimers by means of the 5145 nm line of an argon ion laser was used. The Landé factor for the rovibrational (ν″ = 6.J″ = 52) X_0g⁺ state of ¹³⁰Te₂ molecules has been determined equalling (1.68 ± 0.05) × 10⁻⁴. The result is close to the theoretically predicted one.     

Fast 5d → 4f luminescence of Pr in Lu2SiO5 single crystal host

Absorption and photoluminescence spectra including the decay kinetics of the Pr³⁺-doped Lu₂SiO₅ were measured. Fast luminescence originating from the radiative 5d → 4f transition of Pr³⁺ center is revealed with the maximum at 273 nm at room temperature. Low temperature photoluminescence decay is governed by the 25 ns decay, while substantial shortening to 6–7 ns occurs at room temperature. With the help of slow decay measurement in the millisecond time scale we evidence the thermal ionization of the relaxed excited 5d₁ state of Pr³⁺. The ionization can explain the observed temperature dependences of the decay times and emission intensity.     

Inelastic scattering matrix elements, cross sections and rate constants for transition B(P1/2) + H2(j = 0) ↔ B(P3/2) + H2(j = 0)

The non-adiabatic wave packet collisions of B(²P_1/2) + H₂(j = 0) ↔ B(²P_3/2) + H₂(j = 0) were calculated using the time dependent Channel Packet Method to compute transition probabilities, cross sections and rate constants. While the H₂ angular momentum j was fixed to 0, the total angular momentum of the system J, was varied from 1/2 to 153/2. The feature of the Stückelberg oscillation was shown in transition probabilities. The transition from B(²P_3/2) to B(²P_1/2) state was shown to be favored over the reverse process. The ratio of the computed rate constants was well compared with that of the analytic result obtained from the Boltzmann factor and the detailed balance.