Isolated-core quadrupole excitation of highly excited autoionizing Rydberg states

High lying doubly excited states of the strontium atom are experimentally studied in the vicinity of the Sr$^+(N=5)$ threshold using resonant multiphoton isolated core excitation. Calculations based on configuration interaction with exterior complex scaling are used to analyze the complex spectra we recorded by treating the correlated motion of the two valence electrons of Sr from first principles. The experimental and theoretical spectra reveal the onset of long-range electron correlations and lead to the unambiguous observation, among series of dipole-allowed transitions, of an electric quadrupole isolated-core transition of similar intensity.Comment: 5 pages, 3 figure

High-resolution photoelectron spectroscopy of the ground and first excited electronic states of MgKr⁺

We report on the characterisation of the lowest three electronic states of MgKr+, the X+ 2+ ground state associated with the Mg+(3s) 2 S1/2 + Kr(4p) 6 1 S0 dissociation limit and the A+ 2 ( = 1/2, 3/2) and B+ 2+ excited states associated with the Mg+(3p) 2 P1/2,3/2 + Kr(4p) 6 1 S0 dissocia- tion limits. The vibrational structure of the X+ ground state was measured by pulsed-field-ionisation zero-kinetic-energy photoelectron spectroscopy starting from the a 30 metastable state of MgKr generated by laser ablation of a Mg rod in a Kr supersonic beam. The vibrational assignment was derived from the isotopic structure of the spectra and the adiabatic ionisation energy of the a → X+ ionising transition was determined to be 38182.4(2.0) cm−1 . Partially rotationally resolved spectra of the A+ ← X+ and B+ ← X+ transitions were recorded by monitoring the yield of Mg+ ions produced by dissociation of MgKr+ using the technique of isolated-core Rydberg-dissociation spectroscopy. Analytical potential-energy functions of the X+, A+, and B+ states were derived using a global model of these states that includes the spin-orbit interaction. The observation of the highest vibrational levels of the B+ state and the onset of the Kr + Mg+(3p) dissociation continuum enabled the precise determination of the dissociation energies of the X+, A+ and B+ states of MgKr+ and of the a state of MgKr. The X+, A+ and B+ states of MgKr+ are important stepping stones to access the Rydberg states of MgKr+ and the ground state of MgKr2+ by resonant multiphoton excitatio

Sequential double photodetachment of He− in elliptically polarized laser fields

Four-photon double detachment of the helium negative ion is investigated experimentally and theoretically for photon energies where the transient helium atom is in the 1s2s 3S or 1s2p 3Po states, which subsequently ionize by absorption of three photons. Ionization is enhanced by intermediate resonances, giving rise to series of peaks in the He+ spectrum, which we study in detail. The He+ yield is measured in the wavelength ranges from 530 to 560 nm and from 685 to 730 nm and for various polarizations of the laser light. Double detachment is treated theoretically as a sequential process, within the framework of R-matrix theory for the first step and effective Hamiltonian theory for the second step. Experimental conditions are accurately modeled, and the measured and simulated yields are in good qualitative and, in some cases, quantitative agreement. Resonances in the double detachment spectra can be attributed to well-defined Rydberg states of the transient atom. The double detachment yield exhibits a strong dependence on the laser polarization which can be related to the magnetic quantum number of the intermediate atomic state. We also investigate the possibility of nonsequential double detachment with a two-color experiment but observe no evidence for it

The two-photon detachment of O−^-

International audienc

Experimental and theoretical study of 3-photon ionization He(1s2s 3S) and He (1s2p 3P)

International audienc

One- and two-photon detachment of O−

Cross sections for one- and two-photon detachment of O−(1s22s22p5 2Po) have been determined in a joint experimental and theoretical study. The absolute measurement is based on the animated-crossed-beam technique,which is extended to the case of pulsed lasers, pulsed ion beams, and multiphoton detachment. The ab initio calculations employ R-matrix Floquet theory, with simple descriptions of the initial bound state and the residual oxygen atom which reproduce well the electron affinity and ground-state polarizability. For one-photon detachment, the measured and computed cross sections are in good mutual agreement, departing significantly from previous reference experiments and calculations. The generalized two-photon detachment cross section, measured at the Nd:YAG laser wavelength, is in good agreement with the R-matrix Floquet calculations. Long-standing discrepancies between theory and experiment are thus resolved

Absolute cross sections for the one-photon detachment of O−^-

International audienc

Experimental and theoretical study of three-photon ionization of He(1s 2p 3Po)

A joint experimental and theoretical study of three-photon ionization of the 1s2p 3Po(ML = 0,±1) states of helium is presented. The ion yield is recorded in the 690–730 nm wavelength range for different laser pulse energies, using an excited helium beam produced by photodetachment of helium negative ions. Two series of asymmetric peaks due to two-photon resonances with 1snp and 1snf Rydberg states are observed. In one series, the peaks have tails towards higher frequencies, while in the other series the tails change direction for higher Rydberg states. An effective Hamiltonian is built in the dressed state picture, and a numerical model simulating the traversal of the helium atom across the laser pulse is developed. The simulated and observed ion yields are in good qualitative agreement. The observed behavior is shown to result from the contributions of two different resonantly enhanced multiphoton ionization processes, depending on the magnetic quantum number ML of the initial state. The asymmetry reversal is explained by the strong 1s2p–1s3s dynamic Stark mixing for ML = 0

Absolute total, partial, and differential cross sections for photodetachment of O−

Absolute total, partial, and differential cross sections for the photodetachment of the oxygen anion are reported for photon energies ranging from threshold (1.46 eV) to 5.5 eV. The total cross section was measured using the animated-crossed-beam technique while partial and differential cross sections were obtained using velocity map imaging. The measured values are in good agreement with theoretical results obtained from an R-matrix calculation using polarized pseudostates