Lifetime measurement in the α system (C3Δ3-X3Δ3) of TiO

The radiative lifetimes of two rotational levels of the v′ = 2 level of the C³Δ₃ state of TiO have been measured using laser-induced fluorescence and delayed coincidence counting. Individual rotational levels are excited and observed. The measured lifetimes are τ_{J = 17} = 28.21 + 0.15 nsec and τ_{J = 87} = 29.74 ± 0.86 nsec. Argon-TiO collision cross sections have been determined for the two rotational levels and are found to differ by 30%.     

Excitation spectra and fluorescent lifetime measurements of Mn2+ in CaF2 and CdF2

The excitation spectrum of the Mn²⁺ emission has been measured in CaF₂ and CdF₂. The observed excitation bands have been assigned to transitions of the Mn²⁺ ions in a cubic environment. The calculated values for the crystal field (Dq) and Racah parameters (B,C) are Dq = 425 cm^-1 for CaF₂, Dq = 500 cm^-1 for CdF₂ and, B = 770 cm^-1 and C / B = 4.48 for both compounds. The lifetime of the fluorescent level ⁴T_1g(⁴G) has been measured in both compounds at different temperatures in the range from 10 to 500 K. The lifetime thermal dependence is explained taking into account different mechanisms (purely radiative, phonon assisted, and radiationless transitions) for the decay of excited Mn²⁺ ions.     

Lifetime of the Z1 centre in KC1:Sr

Data on the radiative lifetime τ(Z₁) of the relaxed excited state of the Z₁ centre in KC1:Sr in the 63–135 K range are reported for the first time [τ(Z₁)= 194 ± 10 nsec at 63 K]. The activation energy of deexcitation (ΔE = 0.132 ± 0.008 eV) for the luminescence process is in agreement with the value obtained by Paus from a quantum yield analysis.The results are discussed on the basis of an analogy with the F-centre behaviour.     

Fluorescence of Mn2+ in CaCO3

The fluorescence of Mn²⁺ ion as impurity in CaCO₃ has been investigated. Emission bands from the ⁴D(E_g), ⁴D(T_2g) and ⁴G(T_1g) levels have been observed. The analysis of excitation and emission spectra has allowed to obtain the values of field strength (Dq) for the excited energy levels of Mn²⁺ in CaCO₃ lattice. The temperature dependence of excitation and emission spectra yield an activation energy for thermal quenching of luminescence very close to theoretical calculation. The behaviour of luminescence lifetime with temperature has also been obtained.     

The ν2 fundamental vibration-rotation band of T2O

The ν₂ fundamental vibration-rotation band of T₂O vapor has been measured at grating resolution, and the rotational structure has been analyzed. The band center and the values of the rotational constants A, B, and C for the ground state and excited state have been determined. These values are consistent with the data for J through 6, and with extrapolation from H₂O and D₂O.     

Photoluminescence of F2+2 centres in additively coloured magnesium oxide

The principle luminescence bands excited in additively coloured MgO by radiation in the wavelength range 170–400 nm are observed at wavelengths of 520, 475, 441 and 375 nm. Polarised luminescence and uniaxial stress measurements on the 441 nm band, the radiative lifetime of 25 msec at 1.6 K and temperature dependence of luminescence intensities of the 375, 441 and 375 nm bands are consistent with the 441 nm band being due to ³B_1u → ¹A_g transitions of the F²⁺₂ centre.     

Intensity distributions of fluorescence from the 2B1 state of NO2 excited at 495.0, 474.0, 454.5, and 436.7 nm

Intensity distributions of the fluorescence spectra from the ²B₁ state of NO₂ excited at 495.0, 474.0, 454.5, and 436.7 nm were measured. The vibrational energy levels of the ²B₁ state and the fluorescence intensities from these levels were calculated by means of the theory of the Renner effect developed by Renner, Pople and Longuet-Higgins, and Dixon. Calculated band origins and fluorescence intensities agree with the present measurements, if the vibrational quantum number v′₂ = 15 is assigned to the upper state of the 454.5-nm Douglas-Huber band.     

Ni2+:BeAl2O4晶体发光性质的研究

用时间分辨的激光诱导荧光光谱方法测量了10—300K温度范围内Ni²⁺:BeAl₂O₄晶体的红外荧光光谱和荧光寿命。通过荧光寿命的温度变化特性分析,得出³T_2g态的内禀辐射衰减寿命为123±7.2μs。无辐射弛豫的Mott激活能为1147cm^-1,并导出了此晶体发光量子效率随温度的变化关系式。Ni²⁺:BeAl₂O_{4关键词：}     

The g-factor and lifetime of the 3− (298 keV) state in 16N

The g-factor of the 3^? (298 keV) state in ¹⁶N has been measured by observing the hyperfine modulation of the γ-ray anisotropy in one-electron ions recoiling in vacuum following the ²H(¹⁵N, p)¹⁶N reaction. From the observed spatial frequency the g-factor was deduced to be |g| = 0.532±0.020. Simultaneous lifetime determinations for this state and the 1^? (397 keV) state in ¹⁶N gave values of τm = 131.7±1.9 ps and τ_m = 5.63±0.05 ps, respectively. These and other electromagnetic observables associated with the lowest four levels in ¹⁶N are compared to shell-model calculations.     

Quantum ergodicity in small molecules: The continuum fluorescence of nitrogen dioxide

The failure of selection rules on K_a, v, and vibronic symmetry in the visible band systems of NO₂ are interpreted as resulting from the coupling of the excited electronic state with vibrational levels of the ground electronic state which are above the threshold for ergodic motion and therefore retain no quantization of those observables. This failure is shown to lead directly to the anomalous continuum fluorescence of NO₂, and is intimately related to the anomalous lengthening of the radiative lifetime of the excited state (the Douglas effect). It is predicted that most molecules which exhibit anomalous lifetime lengthening will also exhibit anomalous selection rules and, consequently, anomalous continuum emission.     

Laser fluorescence spectroscopy of 2B1 (K > 0) vibronic states of NO2

The low-pressure fluorescence spectrum of NO₂ excited by the narrow (0.5 GHz) HeCd laser transition at 441.6 nm is found to be quite complex, indicating a rather high density of transitions to final states at this energy. Seven fluorescing states exhibiting perpendicular selection rules have been assigned to ²B₁ (K > 0) vibronic states of NO₂. From the presence of final states with v₃″ = 2, a considerable amount of ²A₂ electronic state character is attributed to at least some of these states.     

Microwave spectrum and molecular force field of tetratomic C2v molecules: NO2Cl

The rotational constants and quartic centrifugal distortion constants for NO₂³⁵Cl and NO₂³⁷Cl have been determined from an analysis of rotational transitions in the microwave and millimeter wave regions between 8.2–40 and 90–120 GHz, respectively.The values of the in-plane force constants in the general harmonic potential field have been obtained by combination of infrared and microwave data. Vibrational frequencies of ¹⁴NO₂Cl and ¹⁵NO₂Cl, inertia defects of NO₂³⁵Cl in the excited vibrational states v₃ = 1 and v₅ = 1, and first-order centrifugal distortion constants of NO₂³⁷Cl are the experimental data used in the least-squares fitting determination of force constants.     

Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

Determination of the radiative lifetime of the d3Πg state of the C2 molecule by the laser-pyrolysis technique. A feasibility study

The feasibility is studied of using the laser-pyrolysis technique for determination of the radiative lifetimes of molecules.Measurements of time-resolved spectral emission were made on spatially resolved sections of the luminous plume produced by laser illumination of a graphite target in a vacuum. The nature of certain emission continua was investigated. The effects on C₂ Swan band emission of focal spot size, illumination power density, height and width of the plasma section observed and its distance from the target were studied. Conditions were determined for measuring physically significant radiative lifetimes for the d³Π_g, v=0 and v=1 levels, of C₂. In particular, the laser flux used was 3.8×10⁸W-cm^?2 while observations were made of a plume section from 0.5 to 0.7 mm from the target. The results, τ(0,0)=235±20 ns, τ(0,1)=250±20 ns, τ(1,0)=255±20 ns, are compared with those obtained by other methods. They are in good agreement with results obtained by pulsed electron excitation. Analysis of the experimental conditions in previous experiments using the laser-pyrolysis technique for measuring τ(d³Π_g of C₂ shows that they could not have lead to meaningful results of purely molecular properties.     

The ν4 and ν2 Raman bands of CHD3

The CHD₃ Raman spectrum from 1925 to 2455 cm^?1 has been photographed with a resolution of about 0.2 cm^?1, showing the overlapping ν₂ and ν₄ bands. Ground state combination differences yield C₀ = 2.6297 ± 0.0003 cm^?1. The ν₄ state is weakly perturbed, but reasonably accurate values could be obtained for ν₄ = 2250.88 ± 0.10 cm^?1, (Cζ)₄ = 0.656 ± 0.010 cm^?1, C₄ - C₀ and B₄ - B₀. Some of these constants differ significantly from values previously estimated by infrared workers. For the ν₂ state the constants determined are in good agreement with recent infrared results.     

Measurement of NO22B2 state g values by optical radio frequency double resonance

The g values for some selected levels of the NO₂ 6126 and 5933 Å bands were measured using optical radio frequency double resonance. The g values are found to be well described by the Hund's case (b) coupling scheme.     

Infrared laser magnetic resonance (LMR) spectroscopy of NO2 (ν2) with a CO2 laser

The infrared laser magnetic resonance spectra for the ν₂ band of NO₂ were observed by using a CO₂ laser. High-K vibration-rotation transitions from ^rR₆(N) to ^rR₁₁(N) (v₂ = 1 ← 0) were observed. The analysis yielded some molecular parameters including two g factors for the excited vibrational state (v₂ = 1).     

The ν5 and ν3 Raman bands of CH2D2

The ν₅ and ν₃ Raman bands of CH₂D₂ have been recorded with a resolution of 0.35 cm^?1. The ν₃ state is well known from infrared studies. Three hundred twenty-nine transitions of the ν₅ band were analyzed, assuming an unperturbed upper state, giving a standard deviation on the fit of the upper-state energies of 0.037 cm^?1, The constants A, B, C, Δ_J, Δ_JK, and Δ_K differed significantly from the ground-state values, and ν₅ was determined as 1331.41 ± 0.05 cm^?1. This work represents the first complete analysis of the fine structure of a rotation-vibrational Raman band for an asymmetric rotor. The ν₅ state could not be analyzed in infrared so this investigation, once more, demonstrates the usefulness of the Raman method.     

A Theoretical Study of ãA2 CH2

The potential energy surface and dipole moment surfaces of the ã⁴A₂ electronic state of CH₂⁺ are calculated ab initio using an augmented correlation-consistent polarized valence quadruple-ζ (aug-cc-pVQZ) basis set, with the incorporation of dynamical correlation using the coupled cluster method with single and double excitations and perturbatively connected triple excitations [CCSD(T)]. We use these surfaces in the MORBID program system to calculate rotation and rotation-vibration term values for ã-state CH₂⁺, CD⁺₂, and CHD⁺ and to simulate the rotation and rotation-vibration absorption spectrum of CH₂⁺ in the ã⁴A₂ electronic state. Our work is motivated by studies of CH₂⁺ that use the Coulomb explosion imaging technique and by the goal of predicting spectra that may be obtained from discharge sources. Although the ã state is the lowest-lying excited state above the X?/Ã ground state pair, it turns out to be relatively high-lying, and we determine that T_e(ã)=30447.5 cm⁻¹. The equilibrium bond angle for ã-state CH₂⁺ is only 77.1°; as a result the asymmetric top κ value is close to 0, and the molecule is equally far from the oblate and prolate symmetric top limits in this electronic state.     

The l-forbidden 1i112 → 2g92 M1 transition in 209Pb

The mean lifetime of the 0.78 MeV first excited state in ²⁰⁹Pb was measured by the recoil distance method to be τ_m = 11.1±1.3 ps. The B(M1) for the l-forbidden transition is in good agreement with one of several recent theoretical predictions.