Rydberg and autoionization tm states investigation by the three-step laser excitation and electric field ionization method

The energies of 190 Rydberg and autoionization 4f ¹³ 6snp-states of the Tm atom (ground electron configuration 4f ¹³ 6s ², nuclear chargeZ=69) have been measured by the laser multistep excitation with subsequent electric field ionization method. The investigation range of these states has been extended towards states with higher and lower values of the principal quantum number. As a result the energies of 160 states have been obtained for the first time. The experiment has been carried out on an automated laser photoionization spectrometer. The measurement accuracy has been ±0.5 cm^?1.     

Doubly-excited 1,3Po autoionization states of He between the N = 4 and N = 6 thresholds of He+ ions

The method of complex-coordinate rotation is used to investigate the doubly-excited ^1,3P^o autoionization states of He between the N = 4 and N = 6 thresholds of He⁺ ions. Resonance energies and total widths for 51 ¹P^o and 51 ³P^o states are reported in the present work. For the singletspin and triplet-spin states, lower-lying resonances for all nine Rydberg series converging on the He⁺ (N = 5) threshold are calculated. For resonances below the He⁺ (N = 6) threshold, we report lower-lying states for eleven and ten Rydberg series for the singlet-spin states and triplet-spin states, respectively. Our results are compared with the experimental observations and with other theoretical calculations when available.     

The Rydberg Nature And Assignments Of Excited States Of The Water Molecule

We report ab initio theoretical calculation on 32 excited states of H₂ O found to lie below 11.7 eV. Of the eight states observed experimentally, the average discrepancy between theoretical and experimental excitation energies is 0.1 eV. We find that the excited states can each be characterized as arising from an excitation to a Rydberg orbital. Our results indicate that the ? and F? states are both 3d-like excited states rather than one 3d state and one 4s state as previously assumed and similarly for the two Rydberg series joining onto ? and F?. The nsa₁ Rydberg series is found to have a quantum defect of 1.38. joining onto the Ã(¹B₁ state. We have assigned the 9.81 eV transition observed by electron impact as the 1b₁ – 3pb₁ excitation to a ³A₁ state.     

Analysis of the Jahn-Teller effect in then p 2 E′ Rydberg series of H3 and D3

Spectroscopic signatures of Jahn-Teller (JT) coupling in then p _x,y ² E′ Rydberg series of H₃ and D₃ are analyzed within a simple multi-channel-quantum-defect-type model. The JT coupling constant has been inferred from existing ab initio calculations of the potential-energy surfaces of low Rydberg states of H₃. The model predicts pronounced resonant perturbations in Rydberg members with intermediaten (n=5–7) as well as strong JT-induced autoionization in absorption and ion-yield spectra from vibrationally excited initial levels. The JT-induced effects are shown to exhibit a characteristic dependence on the vibrational angular momentum of the bending mode in the initial state.     

Tm autoionization rydberg states in the vicinity of the third and fourth atomic ionization limit

The energies of about 200 autoionization Rydberg states of the thulium atom have been measured in the 57380–58960 cm⁻¹ energy region by laser multistep excitation and subsequent autoionization with an accuracy of ±0.4 cm⁻¹. More than a half of the states have been grouped in series. New spectroscopic information has been derived. Three-step two-colour effective excitation schemes have been proposed for thulium atom detection.

     

Autoionization in diatomic molecules: An example of electrostatic autoionization in CO

A review is presented of the different types of autoionization which have been studied theoretically in diatomic molecules: electronic (or electrostatic), rotational, spin-orbit and vibrational autoionizations. An example involving a large number of vibrational channels, is treated. It concerns the electrostatic autoionization in the 730–708 Å wave-length region which appears in the CO photoionization spectrum. The structure observed at 721 Å is explained by the enhancement in intensity of numerous levels of Rydberg series converging to excited vibrational levels of theA ² II state caused by two autoionized Rydberg levels with aB ²Σ⁺ core.     

All-valence-electron CI treatment of the electronic spectrum of trans-butadiene

An all-valence-electron CI treatment is reported for the low-lying valence and Rydberg states of butadiene. All singly- and doubly-excited configurations relative to a series of the leading terms in a given CI expansion are taken into account, with resulting secular equation orders of as high as 150 000. The agreement between calculated and experimental transition energies is invariably better than 0.2 eV where comparison is possible, with all low-lying valence triplet and Rydberg singlet excited states being unambiguously assigned. The valence-shell excitation to the 2 ¹A_g species is concluded to correspond to the 7.06 eV band system, while the forbidden singlet—singlet transition reported by McDiarmid is assigned as x₂ → 3s. The possibility of an avoided crossing between Rydberg valence ¹B_u excited states having a determining influence on the appearance of the broad intense V₁—N absorption is also discussed.     

4pnp J=0e-2e autoionizing series of calcium: experimental and theoretical analysis

The even parity 4pnp J=0, 1, 2 doubly excited autoionizing states of neutral calcium in an atomic beam are investigated by a two-step isolated core excitation (ICE) method using two different combinations of polarization of the laser beams. The different excited energy levels are assigned to nine autoionizing Rydberg series 4p_{1/2, 3/2}np J=0, 1, 2 for ≤ n ≤ 22. The theoretical interpretation is achieved by a combination of the eigenchannel R-matrix theory and the multichannel quantum defect (MQDT) method. Two, five and six closed interacting channels are introduced for the J=0, J=1 and J=2 series respectively. Theoretical energy level positions, autoionization widths and excitation profiles are compared with the experimental data, confirming the identification of the observed structures and providing evidence of extended mixing between the 4p_1/2np and 4p_3/2np series.     

Two-color multiphoton ionization spectra of jet-cooled p-difluorobenzene - s and d Rydberg states

Two-color multiphoton ionization spectra of jet-cooled p-difluorobenzene due to the transitions from S₁ state to highly excited Rydberg states have been observed. At least six different Rydberg series of s and d characters were found. The results indicate a reduction of molecular symmetry in the Rydberg state to C_2h. The Rydberg states belonging to different series exhibit different ionization behavior.     

Jahn-Teller effect in Rydberg series: a multi-state vibronic coupling problem

Two simple limiting cases of Jahn-Teller (JT) coupling in Rydberg states of polyatomic molecules are considered, namely(i) JT coupling in Rydberg orbitals as well as in the ionization continuum (nondegenerate ion core, degenerate Rydberg series) and(ii) JT coupling in the ion core (degenerate ion core, nondegenerate Rydberg series). For both models simple and efficient algorithms for the computation of spectra (dynamical JT effect) are developed. The orbital JT effect is shown to represent a novel type of multi-state vibronic coupling, giving rise to interesting spectroscopic phenomena, among them resonant inter-Rydberg perturbations and JT induced autoionization. Particular attention is paid to the demonstration of the characteristic spectroscopic signatures of the two types of JT coupling in Rydberg states.     

Low-energy dissociative recombination in small polyatomic molecules

Indirect dissociative recombination of low-energy electrons and molecular ions often occurs through capture into vibrationally excited Rydberg states. Properties of vibrational autoionization, the inverse of this capture mechanism, are used to develop some general ideas about the indirect recombination process, and these ideas are illustrated by examples from the literature. In particular, the Δv = -1 propensity rule for vibrational autoionization, i.e., that vibrational autoionization occurs by the minimum energetically allowed change in vibrational quantum numbers, leads to the prediction of thresholds in the dissociative recombination cross sections and rates at the corresponding vibrational thresholds. Capture into rotationally excited Rydberg states is also discussed in terms of recent low-temperature studies of the dissociative recombination of H(3)(+).     

Two-color excitation of NO in a supersonic free jet. Autoionization of high rydberg states

High Rydberg states of NO above the ionization limit have been measured for the isolated molecule in a supersonic free jet by two-color multiphoton ionization. Three Rydberg series (ns, np and nf) were identified, which appeared by rotational and the vibrational autoionization. The rotational structures of the 13s(υ = 1), 13p(υ = 1) and 12f(υ = 1) states have been analyzed in detail. The fluorescence dip spectra for the intermediate A²Σ⁺(3sσ) state have been measured simultaneously and the cross sections of the one-photon absorption to the high Rydberg states from the A²Σ⁺(υ = 1) state have been determined.     

Rydberg states (n = 4–29) of azabicyclo [2.2.2] octane as studied by two-color fluorescence DIP and multiphoton ionization spectroscopies

Two-color fluorescence dip and multiphoton ionization (MPI) spectra have been observed for azabicyclo [2.2.2] octane in a supersonic jet. The spectra showed well-resolved structures consisting of five Rydberg series of n = 4–29. The five Rydberg series were assigned to s, p_z, p_xy, and two d orbitals. From the spectra obtained after exciting the molecule to various vibronic levels in the S₁ (3s) state, the Δν = 0 selection rule was obtained for the Rydberg-Rydberg transition. The same selection rule was found to be preserved also for the transition from the S₁ state to the ion. It was shown that the autoionization of the high Rydberg states to the ion is governed by Δν=?1. The existence of a very fast non-radiative channel was found for the Rydberg state from the ω₂ power dependence on the two-color MPI spectra.     

Electronic spectrum of F<Subscript>2</Subscript>CO: theoretical calculations of vertical excitation energies and intensities

In this work, the linear response formalism with a triples-corrected CCSD reference wave function, LR-CCSDR(3), is applied to the calculation of vertical excitation energies of singlet states of the F₂CO molecule. A basis set of atomic natural orbitals augmented with a series of Rydberg functions has been used in the calculations. A large number of electronically excited states were calculated, and the valence, Rydberg, or mixed character of the states were investigated. In addition, the molecular quantum defect orbital (MQDO) method has been used to determine transition intensities involving Rydberg states. Excitation energies and transition intensities for Rydberg states with n > 3 are reported for the first time.     

MRD CI calculations of excited states of the SiH3 radical,including potential curves for the inversion mode and the dissociation SiH3 → SiH2 + H

Using the MRD CI method and large basis sets the vertical spectrum of silyl radical (SiH₃) has been calculated. The lowest excited state is the 4s Rydberg state, 41000 cm⁻¹ (5.2 eV) above the ground state. Only one excited valence state (2²E) was encountered, all other states are of Rydberg type. From potential curves for the inversion mode (symmetric bending motion) it was inferred that all Rydberg states are planar, whereas the valence excited state is highly pyramidalized. The investigation of the dissociation reaction SiH₃ → SiH₂ + H leads to the conclusion that the first excited state is dissociative.     

Isotope selective two-step photoionization study of K2 in a supersonic molecular beam

The photoionization efficiency curves for ^39,39K₂ and ^39,41K₂ dimers excited to the B ¹Π_u electronic state have been measured using sequential two-photon-ionization techniques. Accurate determinations of nine photoionization thresholds yield an adiabatic ionization energy of 4.06073 ± 0.00016 eV. Autoionizing Rydberg states are assigned and analyzed. Autoionization rates are measured for several Rydberg vibronic states. The isotopic dependence of the autoionization structure is partially analyzed and molecular constants for the K⁺₂ (²Σ⁺_g) state are derived.     

Multiphoton ionization translational spectroscopy (MITS) of I2

A new technique is introduced based on the measurement of kinetic energies and angular distributions of fragments in multiphoton ionization of molecule Both positive and negative ions are measured as well as neutrals. Information is obtained about highly excited repulsive states and about the multiphot ionization process itself. Examples are reported for MPI of I₂. In a one-laser experiment dissociative autoionization is observed. In a two-laser experiment processes are distinguised, that have different intermediate states. Lifetimes of those states are measured. Information is also obtained ab an ion pair formation process, leading to a reinterpretation of potential curves.     

Probing Rapidly‐Ionizing Super‐Atom Molecular Orbitals in C60: A Computational and Femtosecond Photoelectron Spectroscopy Study

Super‐atom molecular orbitals (SAMOs) are diffuse hydrogen‐like orbitals defined by the shallow potential at the centre of hollow molecules such as fullerenes. The SAMO excited states differ from the Rydberg states by the significant electronic density present inside the carbon cage. We provide a detailed computational study of SAMO and Rydberg states and an experimental characterization of SAMO excited electronic states for gas‐phase C₆₀ molecules by photoelectron spectroscopy. A large band of 500 excited states was computed using time‐dependent density functional theory. We show that due to their diffuse character, the photoionization widths of the SAMO and Rydberg states are orders of magnitude larger than those of the isoenergetic non‐SAMO excited states. Moreover, in the range of kinetic energies experimentally measured, only the SAMO states photoionize significantly on the timescale of the femtosecond laser experiments. Single photon ionization of the SAMO states dominates the photoelectron spectrum for relatively low laser intensities. The computed photoelectron spectra and photoelectron angular distributions are in good agreement with the experimental results.