Wavelength and isotopic shift measurements of the3S(3s 4s) −3P(3s 3p) MgI transitions

The wavelengths of the³S(3s 4s) ?³P(3s 3p) MgI transitions have been measured for the²⁴Mg isotope with a precision of ±2 × 10^?7; moreover the isotope shifts of the above transitions have been measured for the three natural Mg isotopes as well as the hyperfine constants of the³S(3s 4s) level of²⁵Mg. The measurements have been performed in a metastable atomic beam.     

Accurate lifetime measurements of the 2p 3d 1 D 0 and 2p 3d 3 P 2 0 levels in N II with the beam-foil-laser method

We have obtained accurate values for the radiative lifetimes of the 2p 3d ¹ D ⁰ and 2p 3d ³ P ₂ ^o levels in NII by the cascade-free beam-foil-laser spectroscopy method. Our results are (2p 3d ¹ D ⁰)=0.346±0.012 ns and (2p 3d ³ P ₂ ^o )=0.457±0.020 ns. Comparison of these results with experimental and recent theoretical lifetimes reported previously is also made.Senior Research Associate of the Belgian FNRS     

Lifetime measurements of the 2p 3d 3 D 1, 2, 3 0 and 2p 3d 1 P 1 0 levels in NII by beam-foil-laser spectroscopy

Accurate lifetimes measured by means of the cascade-free method based on laser excitation of a fast ion beam preexcited in a carbon foil are reported for four 2p 3d levels in NII. The lifetime results are: τ(2p 3d ³ D ₁ ⁰ )=0.209±0.007 ns, τ(2p 3d ³ D ₂ ⁰ )=0.219±0.007 ns, τ(2p 3d ³ D ₃ ⁰ )=0.217±0.005 ns, and τ(2p 3d ¹ P ₁ ⁰ )=0.410±0.017 ns. These results are compared to theoretical and experimental lifetimes reported previously.     

The spin-allowed and spin-forbidden 5s 2 1 S 0-5s5p 1 P 1,3 P 1 transitions in strontium isoelectronic sequence

Relativistic multiconfiguration Dirac-Fock (MCDF) transition energies and oscillator strengths are determined for both the spin-allowed 5s ^{2 1} S ₀-5s5p ¹ P ₁ and the spin-forbidden 5s ^{2 1} S ₀-5s5p ³ P ₁ transitions in the strontium isoelectronic sequence. The modest relativistic configuration mixing to represent intravalence correlation is combined with a polarization model to account for valence-core electron correlations. The multiconfiguration Dirac-Fock calculations are performed in an average level scheme; however for neutral strontium and singly ionized yttrium a thorough comparison of the average and the optimal level schemes is presented. The average level scheme, though less accurate for the neutral end of the sequence, avoids the convergence problems encountered for highly ionized systems, where the 5s 5p ³ P ₁,¹ P ₁ states are raised owing to the collapse of the 4d _{3/2, 5/2} spin-orbitals in the isoelectronic sequence and, thus, allows us to extend our study to multiple charged ions (throughW ³⁶⁺). Since for such systems there is practically no difference between the results of the average and the optimal level versions of MCDF calculations, we believe that our average level predictions of ionization energies and oscillator strengths for states with total angular numberJ=0 andJ=1 are of comparable quality to those that could be obtained with an optimal level scheme.This study was supported by the Pedagogical Academy of Kraków Statutory Activity Grant No BS-29/91     

Radiative lifetimes of the 6p 2 P 1 2/0 and 6p 2 P 3 2/0 levels in Yb II

Radiative lifetimes have been determined for the 6² P ₁ ^2/0 and 6² P ₃ ^2/0 levels in Yb II using the method of laser-induced fluorescence from sputtered metal vapour. The results, 8.0(2)ns (6² P ₁ ^2/0 ) and 6.3(3)ns (6² P ₃ ^2/0 ), are compared with lifetimes obtained from ab initio manybody perturbation calculations.     

Photodissociation of N2O: triplet states and triplet channel

The role of triplet states in the UV photodissociation of N(2)O is investigated by means of quantum mechanical wave packet calculations. Global potential energy surfaces are calculated for the lowest two (3)A' and the lowest two (3)A' states at the multi-reference configuration interaction level of electronic structure theory using the augmented valence quadruple zeta atomic basis set. Because of extremely small transition dipole moments with the ground electronic state, excitation of the triplet states has only a marginal effect on the far red tail of the absorption cross section. The calculations do not show any hint of an increased absorption around 280 nm as claimed by early experimental studies. The peak observed in several electron energy loss spectra at 5.4 eV is unambiguously attributed to the lowest triplet state 1(3)A'. Excitation of the 2(1)A' state and subsequent transition to the repulsive branch of the 2(3)A' state at intermediate NN-O separations, promoted by spin-orbit coupling, is identified as the main pathway to the N(2)((1)Σ(g)(+))+O((3)P) triplet channel. The yield, determined in two-state wave packet calculations employing calculated spin-orbit matrix elements, is 0.002 as compared to 0.005 ± 0.002 measured by Nishida et al. [J. Phys. Chem. A 108, 2451 (2004)].     

Electron-impact ionization of the metastable Mg(...2p63s3p3P0,2) atoms

Electron-impact ionization of Mg atoms from metastable states was investigated. The method and tech-nique of crossed atomic and electron beam studies are described. The value of the total ionization cross section from the 3s3p ³P_j metastable states for 4... 21 eV incident electron energy was determined. It was found that ionization cross sections from the metastable and ground states differ considerably. This is mainly due to the different mechanisms of ion formation from the metastable and ground states. The results obtained are compared with those calculated in the classical mechanics binary approximation.     

Oscillator strength measurements of the 5s5p 3P1 → 5snd 3D2 Rydberg transitions of cadmium

We report oscillator strengths distribution in the bound region of cadmium corresponding to the 5s5p ³P₁ → 5snd ³D₂ (21 ≤ n ≤ 52) Rydberg transitions. The experiment was performed using two frequency doubled dye lasers simultaneously pumped by a common Nd:YAG laser in conjunction with an atomic beam set-up. The absolute photoionization cross section of the 5s5p ³P₁ intermediate state at the 5s ²S_1/2 ionization threshold has been measured as 20 (4) Mb using the saturation technique. The measured value of the photoionization cross section at threshold is used to extract the f-values of the above mentioned Rydberg transitions.     

Lifetime measurement of some levels belonging to 3p 4 4p configuration of Ar II

High frequency deflection technique with delayed coincidence single photon counting arrangement has been used to measure the lifetimes of some excited states of argon II. The measurements have been performed under conditions where pressure-dependent effect is negligible. The instrumental response function has been obtained directly and the measured decay curves have been deconvoluted using this response function to yield the lifetimes of the levels concerned.     

Precision energies and hyperfine structures of the 5s5p 3 P 0,1,2 0 and 5s6s 3 S 1 levels in In II

Absolute frequencies of hyperfine components of the 230.6 nm (5s ^{2 1} S ₀?5s5p ³ P ₁ ⁰ ), 193.6 nm (5s5p ³ P ₀ ⁰ ?5s6s ³ S ₁), 197.7 nm (5s5p ³ P ₁ ⁰ ?5s6s ³ S ₁) and 207.9 nm (5s5p ³ P ₂ ⁰ ?5s6s ³ S ₁) transitions in In II emitted from a hollow-cathode source have been measured using a high-resolution, scanning échelle monochromator. The measured frequencies of these four transitions have been used to determine the energies and hyperfine interaction constants of the 5s5p ³ P ₀ ⁰ ,³ P ₁ ⁰ ,³ P ₂ ⁰ and 5s6s ³ S ₁ levels in In II. The hyperfine interaction constants for the dominant isotope¹¹⁵In are found to be: 5s5p ³ P ₁ ⁰ A=0.2322(2) cm^?1,B=?0.0159(9) cm^?1 5s5p ³ P ₂ ⁰ A=0.1699(4) cm^?1,B= 0.021 (6) cm^?1 5s6s ³ S ₁ A=0.4022(4) cm^?1,B= 0.002 (2) cm^?1. The absolute frequency of the very narrow, strongly forbidden In II 236.5 nm (5s ^{2 1} S ₀?5s5p ³ P ₀ ⁰ ) transition, which has been proposed as a candidate for a new optical frequency standard, is found to be 42275.986(7) cm^?1.     

Hyperfine structure and Zeeman effect studies in the 6p7p-6p7s transitions in Bi II

The hfs and hfs Zeeman splitting of nine lines from the array 6p7p→6p7s as well as lines λ = 496.9 nm (6p8p ³D₂→6p7s ³P₂) and λ=581.8 nm (6p8s ³P₀→6p7p ³D₁) of Bi II have been analysed. The Zeeman effect studies were performed for transverse direction of observation and separated π; and σ components of lines. The electrodeless discharge tube containing metallic Bi was used as the light source. The spectral apparatus consisted of a sliver-coated Fabry-Perot etalon and a grating spectrograph combined with a diode array detector. In the analysis of the spectra we used the computer simulation technique. The magnetic-dipole (A) and the electric-quadruple (B) hfs constants as well as Lande-g_j factors for the level 6p8p ³D₂ and all levels of configurations 6p7s and 6p7p (with the exception of 6p7p ³S₁) were determined. Our results are compared with recent theory and other experiments.     

Reaction Dynamics of Mg(3s3p1P1) with H2

We measured the temperature dependence of rotational population distribution of the nascent product MgH(²∑⁺) in the reaction of Mg(3s3p¹P₁) with H₂. The results indicate that the reaction is dominated by an Mg-insertive mechanism, consistent with the isotope effect reported previously. We also presented the vibrational population distribution, and thereby found that two parallel reaction pathways are responsible for the subject reaction following Mg-H₂ collision in a bent configuration. The major one produces MgH in higher rotational levels and comparable v″ = 0 and v″ = 1 populations, while the other minor one produces MgH in low rotational levels and preferentially v″ = 0. By means of a two-dimensional potential energy sur-face(PES) calculation, a deep insight into the reaction pathways has been gained. The resulting PES's information reveals the possibility of a nonadiabatic transition between the excited ¹B₂ PES and the ground PES. The bent intermediate MgH₂ near the surface crossing starts trajectories either smoothly following the dissociation coordinate of Mg-H distance or attractively falling down through a linear HMgH geometry before breaking apart. The former trajectory accounts for the minor reaction pathway to produce MgH, while the latter one responses to the major reaction pathway. The impact of isotope and temperature effects on MgH can also be readily explained with use of the calculated PES's.     

Spectroscopy and kinetics of the 1P1 and 3P2 states of Hg 6s6p in xenon

The spectra and kinetics observed following excitation of Hg 6s6p(¹P₁) in xenon show the occurence of complex attachment and relaxation processes. The ¹P₁ attaches to Xe in termolecular collisions to produce HgXe E¹1, which emits a broad band with λ_max ≈ 2150 Å. Addition of krypton to Hg, Xe mixtures enhances the E-state emission by atom exchange with an HgKr^* complex. The E state also undergoes collisional deactivation by Xe, rate coefficient (1.75 ± 0.25) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, to generate ³P₂. However, the predominant route for ³P₂ formation is via collision of ¹P₁ with Xe, rate coefficient ≈ 4 × 10⁻¹² cm³ molecule⁻¹ s⁻¹. With [Xe] at 760 Torr, about 75% of the generated ³P₂ is attached in the form of the HgXe(C ³2) complex; lifetimes up to 600 μs have been observed. Two new emission bands occur when ³P₂ is prepared in xenon. A sharp feature, slightly blue-shifted from the forbidden ³P₂:¹S₀ line, results when ³P₂ and Xe approach on the D ³1 surface. The other band is broad with λ_max ≈ 2520 Å; the carrier is assigned to an HgXe₂(³2_u) complex. Rate coefficients for deactivation of ³P₂ to lower ³P_J states have been measured.     

Lifetimes of the 4s4p 3 P 1 and 4s3d 1 D 2 states of Ca I

The lifetimes of the 4s4p ³ P ₁ and 4s3d ¹ D ₂ metastable states of Ca have been studied using the time-of-flight technique. Two kinds of observations were performed. First, the exponential decay of the fluorescence, using a (continuous) dc discharge for excitation and then the velocity distribution of the radiating atoms, using a pulsed discharge, were measured. From the combined results of these measurements the lifetimes were derived. The lifetimes of the 4s4p ³ P ₁ and 4s3d ¹ D ₂ states of Ca are determined to be 0.57±0.03 ms and 1.5±0.4 ms, respectively.     

Intercombination decay of 3s3p 3 P 1 0 in MgI-like Ni and Cu

The intercombination transition 3s^{2 1}S₀ ?3s3p³P ₁ ⁰ in Ni¹⁶⁺ and Cu¹⁷⁺ has been studied by beam-foil spectroscopic methods. Decay curve analysis yields lifetime values of (12.0±1.0)ns and (8.8±0.6)ns for Ni and Cu in agreement with various predictions.     

Effect of the exchange integral K2s2p on the 2p-orbitals of the 1P and 3P states of the beryllium isoelectronic sequence arising from the configuration (1s)2(2s)(2p)

The ¹P and ³P states arising from the configuration (1s)²(2s)(2p) of the Be isoelectronic sequence are investigated. In the single configuration approximation, the energies of the two states are expressed as E⁰ + K_2s2p and E⁰ - K_2s2p, respectively. K_2s2p is the exchange integral between the 2s and 2p electrons and E⁰ is the energy of a model in which K_2s2p is deleted. First we calculate the 2s- and 2p-orbitals in this model. Second, by taking account of K_2s2p in this model, effects of this term on the 2p-orbitals in the ^1,3P states are investigated. In this manner, an explanation is given for the following facts which are obtained from a minimal Slater-type orbital set; (1) for Be and B⁺, the 2p-orbital of the ¹P state is broader than that of the ³P state; (2) for C²⁺, the extension of the 2p-orbital in the two states is almost the same; (3) for O⁴⁺ and Ne⁶⁺, in contrast to Be and B⁺, the 2p-orbital of the ¹P state is tighter than that of the ³P state.     

HFS constants of Be I 1s22s2p 3p0, B I 1s22s2p24P and B I 1s22s2p22D obtained from the non-closed shell many-electron theory for excited states

Using the non-closed shell many-electron theory for excited states of Sinano?lu we compute the hyperfine structure constants of Be I 1s²2s2p ³P⁰, B I 1s²2s2p²⁴P and B I 1s²2s2p²²D. The quadrupole moment of ⁹Be is also newly determined to be, Q = 0.05494 barns.     

Lifetime of the metastable 6P 3/2 level of PbII

Pb⁺-ions were stored in a r.f.-quadrupole trap. Short laser pulses at a 710-nm M1-transition excited the ions to the metastable 6P _3/2 level. Time-resolved registration of the subsequent decay photons at the same wavelength directly gives the lifetime of that state. No dependence of the decay rate on the density of different buffer gases up to 10^?5 mbar pressure was observed and from this we deduced upper limits to the quenching cross section. We have observed, however, a small dependence on the stored ion number. The final result for the lifetime is 41.2 ± 0.7 ms in agreement with the result of a previous calculation.