Saturation spectroscopy of NH2 using a CW dye laser

Hyperfine structure in the electronic spectrum of NH₂ has been resolved using the technique of intermodulated fluorescence with CW dye laser excitation. From the observed spacings values for the ¹⁴N Fermi contact and dipole-dipole coupling terms have been estimated for both the ground state and the Π(0,10,0) vibrational level of the à ²A₁ excited electronic state.     

Fine structure and transition probabilities of the 2p 5 nl bound excited states of Ne atom

We present a semi-empirical calculational procedure for thep ⁵ nl bound excited states of rare gas atoms based on the use of an LS-dependent orbital for an excitednl electron outside a frozen Hartree-Fockp ⁵ core. The spin-orbit interaction is accounted for approximately using a localized Hartree potential. The contribution from the long-range core polarization is estimated by using a parametrized potential. A model potential is also introduced to represent partially the short-range multi-electron interactions for thep ⁵ np levels. The energy levels are calculated by diagonalizing the Hamiltonian matrix following anLS →jl transformation. The calculated fine structure of the Nep ⁵ ns,p ⁵ np,p ⁵ nd, andp ⁵ nf ¦ (jl)KJ〉 levels are in close agreement with the observed level splittings. The transition probabilities are also in agreement with earlier theoretical and experimental results.     

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.     

Measurement of hyperfine structure of sodium 3P 1/2,3/2 states using optical spectroscopy

The hyperfine levels of the sodium 3P _1/2,3/2 states were resolved using a narrow linewidth laser to excite the ground state. The laser frequency was scanned while fluorescence resulting from the radiative decay of the excited state was detected. The frequency was calibrated using the known hyperfine splitting of the ground state. The magnetic dipoleA and electric quadrupoleB hyperfine coupling constants of the excited states were determined to be $A_{3P_{1/2} } = 94.44 \pm 0.13$ , $A_{3P_{3/2} } = 18.62 \pm 0.21$ and $B_{3P_{1/2} } = 2.11 \pm 0.52MHz$ . The uncertainty of $A_{3P_{1/2} } $ is less than results previously reported while the data for the 3P _3/2 state are consistent with those existing in the literature.     

Interference effects in Stark spectra of weakly autoionising 5dnf states of barium

Weakly autoionising 5d _3/2 nf Rydberg states of barium around n = 60 have been studied in the presence of a static electric field. The experiment has been carried out in a CW laser-atomic-beam setup. In between the overlapping n = 60 and 61 angular momentum manifolds broad 5d63d resonances interact with the manifold states resulting in pronounced interferences. These interferences (anti-crossings) have been analysed by a direct diagonalisation procedure neglecting interactions with the continuum, and by a Multichannel Quantum Defect Theory (MQDT) analysis including continuum interactions.     

Rydberg states of the K2 molecule studied by laser spectroscopy in a supersonic beam

Rydberg states of potassium dimer have been studied in a crossed laser-molecular beam experiment. The K₂ molecules were formed in a supersonic expansion and excited by low-power cw dye laser. Two different excitation schemes have been used: The first scheme uses a single mode ring dye laser to induce near resonant two-photon transitions while in the second scheme stepwise excitation with two dye lasers is used. In each case excitation of Rydberg levels was detected by monitoring the ionization signal resulting from three-photon absorption. We report a detailed study of 700 two-photon resonances between 625 nm and 650 nm. Most of these signals can be assigned to transitions from the X¹σ _g ⁺ to¹σ _g ⁺ ,¹Π _g , and^1Δ _g states, which are all enhanced by the B¹Π _u intermediate state. Accurate rotational constants are given for the populated vibrational levels of these states. By stepwise excitation of Rydberg levels via theB ¹Π _u state we identify 3 series of Rydberg states as¹Δ _g (4S+nD),¹Σ _g ⁺ (4S+nD), and¹Σ _g ⁺ (4S+nS) with principal quantum numbers 7≦n≦20. Molecular constants of these and other observed but as yet unidentified states are given; quantum defects and dissociation energies are discussed.     

Laser and radio-frequency spectroscopy of the 5d 36s 2 4 P 3/2,5/2 states in Ta I

The hyperfine structure of the metastable atomic states 5d ³6s ^{2 4} P _3/2 and⁴ P _5/2 in¹⁸¹Ta has been studied using high resolution laser spectroscopy and laser radio-frequency double-resonance methods.     

Picosecond fluorescence spectroscopy with a CW laser and a radio — a simple technique

A simple picosecond-domain lifetime measurement technique is described, wherein ac null detection is performed with two modulated light beams, one from the sample, the other an optically delayed part of the excitation, both falling onto a single detector.     

Study of the catalytic decomposition of 2-propanol induced by CW?CO2 laser

The decomposition of 2-propanol induced by CW–CO₂ laser with and without catalyst has been studied. In the presence of catalyst the threshold laser energy for stimulating decomposition is decreased. The reaction products depend on the adsorption states of 2-propanol on the catalyst surface. The mechanism of laser induced surface reaction is discussed.     

Photoassociation spectroscopy of ultracold Cs below the 6P(3/2) limit

High precision photoassociation spectroscopy is performed in ultracold cesium gas, with detunings as large as 51 cm(-1) below the Cs(6S(1/2))+Cs(6P(3/2)) asymptote. Trap-loss fluorescence detection is used for detecting the photoassociation to excited state ultracold molecules. Long vibrational progressions are assigned to electronic states of 0(g) (-), 0(u) (+), and 1(g) symmetry. The spectral data are fitted to a LeRoy-Bernstein equation, in order to obtain the effective coefficients of the leading long-range interaction term (C(3)/R(3)) and the relative vibrational quantum numbers measured down from dissociation. Additionally we present evidence for perturbations between the 0(g) (-) state and the dark 2(u) state.     

Investigation of lutetium rydberg states by laser multistep resonance ionization spectroscopy

Laser multistep excitation and electric-field ionization spectroscopy have been used to investigate experimentally highly excited states (HES) of lutetium in the vicinity of the first ionization limit. The investigation includes the measurement of energy levels (ionic signal vs last transition frequency) and radiation lifetime (ionic signal vs ionizing electric-field pulse delay) of the states investigated. Even Rydberg states of 4f ¹⁴ 6s ² nd have been observed with two-step laser excitation. The maximum experimental error is 0.3 cm^?1 for the energy and 20% for the radiation lifetime measurements. This is the very first time that results for the lifetimes as well as for a large part of the energy values have been obtained. Our present experimental results compare well with previously calculated values obtained by relativistic perturbation theory using the zero-order model approximation, and with the available experimental values.     

Electron dynamics in charge-transfer-to-solvent states of aqueous chloride revealed by Cl- 2p resonant Auger-electron spectroscopy

Charge-transfer-to-solvent (CTTS) excited states of aqueous chloride are studied by a novel experimental approach based on resonant inner-shell photoexcitation, Cl(-)aq 2p --> e(i), i = 1-4, which denotes a series of excitations to lowest and higher CTTS states. These states are clearly identified through the occurrence of characteristic spectator Auger decays to double Cl 3p valence-hole states, where the CTTS states can be more stabilized as compared to single Cl(-)aq 2p core excitations and optical valence excitations. Furthermore, we have found for the first time that the CTTS electron e(i) bound by a single Cl 2p hole not only behaves as a spectator e(i) --> e'(i), bound by a double valence-hole state before relaxation of the excited electron (i) itself, but also shows electron dynamics to the relaxed lowest state, e(i) --> e'(1*). This interpretation is supported by ab initio calculations. The key to performing photoelectron and Auger-electron spectroscopy studies from aqueous solutions is the use of a liquid microjet in ultrahigh vacuum in conjunction with synchrotron radiation.     

Stark-mixing effect on the 6p 2 1 S 0−6p 2 3 P 2 transition in Pb I

The intensity of the 531.5 nm electric-field-quench radiation has been measured on a thermal beam of neutral Pb atoms in the metastable 6p ^{2 1} S ₀ state. The measurement yields a Stark-mixing amplitude for transition between the 6p ^{2 1} S ₀ and 6p ^{2 3} P ₂ states. Combining this result with available experimental data sets an upper limit for the 6p 7s ³ P ₁ → 6p ^{2 1} S ₀ transition probability:A _ki <1.79·10³ s ^?1. Calculations for the 6p 7s → 6p ² and 6p 8s → 6p ², as well as transition rates of forbidden lines inside 6p ² configuration of PbI are presented and compared with existing experimental data.     

Calculation of 2p 4(3 P)nl(l=s,d) Rydberg spectra of the fluorine isoelectronic sequence

The basic structure parameters of 2p ⁴(³ P)ns and 2p ⁴(³ P)nd (J=1/2, 3/2 and 5/2) Rydberg spectra for the fluorine isoelectronic sequence from FI to NiXX, as functions of effective nuclear charge, are calculated by using the eigenchannel quantum-defect theory. The results can be interpreted in terms of the variations of electrostatic and spin-orbit interactions along the sequence. A vast amount of basic atomic data can be obtained with these parameters as input. Some numerical examples are given, in which our results are in perfect agreement with experimental.     

Two photon photodetachment spectroscopy: The C2σ states

A tunable dye laser has been used to observe resonant two photon photodetachment of electrons from C⁻₂. These measurements definitely establish the fact that the Herzberg-Lagerquist band system belongs to C⁻₂, and that the ground state of C⁻₂ is a ²σ⁺_g state. The two photon photodetachment technique is described, and future potentialities are assessed.     

Two-colour bound—free—bound spectroscopy of the [E1/2]c6S Rydberg states of CH3I and CD3I

In this resonantly enhanced multiphoton ionization (REMPI) experiment, an extended vibrational progression in the CI stretching mode (v₃) of methyl iodide (-h₃ and -d₃) is observed in the 1 + 1′ excitation of the [1/2] 6s; 0 Rydberg state when the pump photon wavelength lies in the bound → free absorption continuum. This is in contrast with one-colour coherent (non-resonant) two-photon excitation, where the v₃ mode is not excited. By working at several different fixed probe wavelengths and scanning the pump frequency, the relative contributions from the three intermediate repulsive states can be explored through changes in the relative strengths of the Ω = 0 and 1 components of the final Rydberg states. Extensive predissociation in the Rydberg states curtails the vibrational progression.     

Lifetime measurements of the 3D3/2 and 3D5/2 metastable states in CaII

The lifetime of the metastable 3D_3/2 and 3D_5/2 states of Ca⁺ ions is determined in a r.f. ion trap by laser excitation of this levels and subsequent time delayed probing of the state population by a second laser. In a buffer gas atmosphere of about 10^–5–10^–6 mbar of He we observe quenching to the ground state and strong finestructure mixing of the two D-states. This mixing allowes only the determination of the combined lifetime. Our result of (3D)=1.24(39) s is in good agreement with theoretical calculations.     

High-resolution laser spectroscopy of the AΠu-XΠg system of Br2

The laser excitation spectrum of the Br₂⁺ molecular ion was observed at rotational resolution for the first time, with the ions being generated by Penning ionization. In contrast to Cl₂⁺ and F₂⁺ but in agreement with recent theoretical work, no vibrational or rotational perturbations are observed. The data from a number of vibrational bands are fitted simultaneously to give reliable estimates of the Dunham rotational and vibrational constants. This fit indicates that the vibrational numbering used in previous studies should be increased by 1 in the upper state.     

High-resolution laser excitation spectroscopy of the A2E-X2A1 transition of SrCH3

High-resolution laser excitation spectroscopy has been used to record the A (2)E-X (2)A(1) electronic transition of SrCH(3) in a laser ablation/molecular jet source. Transitions arising from the K(')=1<--K(")=0, K(')=0<--K(")=1, and K(')=2<--K(")=1 subbands have been observed and assigned. The data were modeled with (2)E and (2)A(1) symmetric top Hamiltonian matrices in a Hund's case (a) basis, using a least squares fitting program. Rotational and fine structure parameters for the A (2)E state were determined. A comparison of the spin-orbit energy separation in the A (2)E state to other strontium containing free radicals showed that the Jahn-Teller effect is negligible. The spin-rotation constants for the A (2)E state were calculated using the pure precession model and were found to be in good agreement with the experimentally determined parameters. These calculations suggest that the A (2)E state of SrCH(3) is not entirely of p orbital character. The rotational constants were used to estimate the structural parameters of SrCH(3) in the A (2)E state. The strontium-carbon bond length was found to decrease by approximately 0.006 A, and the hydrogen-carbon-hydrogen bond angle opened by approximately 0.8 degrees compared to the X (2)A(1) state, similar to the geometry changes observed for CaCH(3).