Characterization of the excited states of ethylene by MRCI

The excited states of ethylene are systematically analyzed and characterized according to the natural orbitals (NOs) resulting from multireference configuration interaction singles and doubles (MRCISD) calculations. By comparing the shapes and nodal structures of the NOs with those of hydrogen atomic orbitals, the Rydberg series can be classified. Two or three different types of Rydberg series appear within five excited states for each symmetry of D_2h. For example, in the ¹A_g symmetry there are three series having np and two nf hydrogen‐like atomic orbitals. Electronic correlation effects for the (π→π*) V state are also discussed on the basis of a complete active space self‐consistent field (CASSCF) calculation, showing that electron correlation effects merely within the valence space cannot explain contraction of the V state. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Theoretical calculation about the valence and Rydberg excited states of hydrogen cyanide

The singlet and triplet excited states of hydrogen cyanide have been computed by using the complete active space self-consistent field and completed active space second order perturbation methods with the atomic natural orbital (ANO-L) basis set. Through calculations of vertical excitation energies, we have probed the transitions from ground state to valence excited states, and further extensions to the Rydberg states are achieved by adding 1s1p1d Rydberg orbitals into the ANO-L basis set. Four singlet and nine triplet excited states have been optimized. The computed adiabatic energies and the vertical transition energies agree well with the available experimental data and the inconsistencies with the available theoretical reports are discussed in detail.     

Dynamic polarizabilities and Rydberg states of open shell atomic systems

Time dependent coupled Hartree-Fock (TDCHF) theory is applied to calculate frequency dependent polarizabilities, transition energies, oscillator strengths and effective quantum numbers of several excited states of the open shell ions Al, Si⁺, P²⁺, S³⁺, Cl⁴⁺, Ar⁵⁺, Cl and Ar⁺ in the ²P state within and beyond the normal dispersion region. The Roothaan formalism has been adopted to deal with the open shell problem. The excitation energies are extracted from the positions of the poles of an appropriate functional. Analytic representations of the singly excited Rydberg states have been found. The results obtained compare well with spectroscopic and other elaborate theoretical data wherever available. Inner shell excitations have been found for the first time within TDCHF theory.     

On the Electric Field Effect on the Dynamics of High Rydberg States of Hydrogen Atom and the Model of ZEKE Spectroscopy

In this paper, the studies of the dynamics of the high Rydberg states for n = 10 and n = 100 of hydrogen atom under the influence of an electric field will be reported. It will be shown from our calculated results that the two time constants of τ_slow ≈? 1 – 10 μs and τ_fast ≈? 1 – 10 ns obseved in ZEKE experiments are obtained in the stray field condition, i.e., F = 10 – 100 mV/cm. To treat the ZEKE states of complex systems like many-electron atoms, molecules, clusters etc., the inverse Born-Oppenheimer approximation can be used and it will be discussed.     

Degenerate symmetry-adapted perturbation theory of weak interactions between closed- and open-shell monomers: application to Rydberg states of helium hydride

Symmetry-adapted perturbation theory is extended to the (quasi) degenerate, open-shell case. The new formalism is tested in calculations of the interaction energies for a helium atom in the ground state interacting with an excited hydrogen atom. It is shown that the method gives satisfactory results if the coupling with higher Rydberg states of the dimer is small, as is the case for the A²Σ⁺,B²Π,E²Π,3²Π, and 1²Δ states of HeH. For the C²Σ⁺ state convergence of the method is very slow, but it can be improved by including the n=3 states in the model space. Received: 3 June 1998 / Accepted: 9 September 1998 / Published online: 7 December 1998     

Dynamic behavior of highly excited molecular states in the strong monochromatic laser fields

The dynamic behavior of highly excited molecular states in an external monochromatic field has been investigated in order to establish the general trends in the Rydberg state manifestations in collisional and radiative processes. The effects of interference between direct (background) and resonant interactions and coupling between the continua on the fine structure of collision cross sections and near-threshold photoabsorption spectra are discussed. Analytical expressions for the widths and intensities of the Rydberg lines induced by mixing the field with other quasistationary states are derived and their dependence on the external field strength and frequency are analyzed. It was found that the appreciable stabilization of isolated Rydberg levels observed previously in superstrong fields is also possible in fields much weaker than atomic fields. The possibility of laser control for the energy averaged cross sections and reaction rate constants are considered. All effects are illustrated for thee ^– + H₂ ⁺ system.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 367–386, March, 1994.This work was supported by the Russian Foundation for Basic ReSearch (Grant No. 93-03-4700).     

One-Electron Pseudo-Potential Determination of Stable Isomers of the Li*Ar n Excited Clusters: Absorption Spectra

We present pseudo-potential calculations of geometrical structures of stable isomers of LiAr _n clusters with both an electronic ground state and excited states of the lithium atom. The Li atom is perturbed by argon atoms in LiAr _n clusters. Its electronic structure obtained as the eigenfunctions of a single-electron operator describing the electron in the field of a Li⁺Ar _n core, the Li⁺ and Ar atoms are replaced by pseudo-potentials. These pseudo-potentials include core-polarization operators to account for the polarization and correlation of the inert core with the valence Lithium electron [J Chem Phys 116, 1839 1]. The geometry optimization of the ground and excited states of LiAr _n (n = 1–12) clusters is carried out via the Basin-Hopping method of Wales et al. [J Phys Chem 101, 5111 2; J Chem Phys 285, 1368 3]. The geometries of the ground and ionic states of LiAr _n clusters were used to determine the energy of the high excited states of the neutral LiAr _n clusters. The variation of the excited state energies of LiAr _n clusters as a function of the number of argon atoms shows an approximate Rydberg character, corresponding to the picture of an excited electron surrounding an ionic cluster core, is already reached for the 3s state. The result of optical transitions calculations shows that the absorption spectral features are sensitive to isomer structure. It is clearly the case for transitions close to the 2p levels of Li which are distorted by the cluster environment.     

Ionization thresholds and positions of avoided crossing of potassium Stark Rydberg states: a Stark-adapted quantum defect orbital treatment

We have calculated the positions of the avoided level crossings between (n+2)s, np states and nd, k Stark states in the Rydberg Stark states of the potassium atom with principal quantum number n comprised between 12 and 17. We have also studied the adiabatic electric field ionization thresholds for the above Rydberg states. Both the ionization thresholds and the positions of avoided crossings have been calculated using the recently developed Stark-adapted quantum defect orbital (SQDO) formalism. The presently reported values appear to be in very good agreement with the available theoretical and experimental data.     

Vibronic spectra of the allyl radical at 6–8 eV with resonance-enhanced multiphoton ionization technique

The allyl radical was produced in molecular beam by pyrolysis of allyl iodide. The vibronic spectra from ground state to six new electronic states of the allyl radical at 6–8 eV, π →3d^xz, π →3d^xy and π →ns (n=4, 6, 7, 8) were observed firstly with the aid of time-of-flight mass spectros copy and resonance-enhanced multiphoton ionization technique. Vibrational progression ofv ₇(C₃ bend) with gross spacing of about 430 cm⁻¹ was observed inns Rydberg states. The adiabatic ionization potential of the allyl radical was obtained to be (65641 ± 20) cm⁻¹ ((8.138 ± 0.002) eV) by fitting the term values ofns (n=4,6,7,8) Rydberg states with Rydberg formula.     

Rydberg character of the higher excited states of free-base porphin

 The Rydberg character of the excited states of free-base porphin (FBP) has been investigated by the ab initio configuration interaction singles (CIS) method and the state-averaged complete-active-space self-consistent-field method. Double-zeta basis sets augmented with s, p, and d Rydberg functions and d polarization functions have been employed. Two types of molecular orbitals sets, the restricted Hartree–Fock molecular orbitals obtained for the ground state (¹A _g ) and for the cation state (²A _u ), have been used in the CIS calculations. All the calculations show that Rydberg-type excitations play important roles especially in the N bands. In this article we propose applying the model of a perturbed Rydberg series to interpret the excited states of FBP. By using this model, we have succeeded in analyzing the characteristics of the excited states as well as the experimental oscillator strengths, which have considerable magnitude even in the higher excited states. Received: 27 November 2000 / Accepted: 11 April 2001 / Published online: 27 June 2001     

The valence and Rydberg excited states of CH2: A theoretical exploration

Using the completed active space second‐order perturbation (CASPT2) method, valence and Rydberg excited states of CH₂ molecule are probed with the large atomic natural orbital (ANO‐L) basis set. Five states are optimized and the geometric parameters are in good agreement with the available data in literatures, furthermore, the state of 2¹B₁ is obtained for the first time. Valence and Rydberg excited states of CH₂ are also calculated for the vertical transitions with the ANO‐L+ basis set that is constructed by adding a set of 1s1p1d Rydberg orbitals into the ANO‐L basis set. Two Rydberg states of the p?³A₂ and r?³B₁ at 9.88 and 10.50 eV are obtained for the first time, and the 3a₁ → 3d_yz nature of the state p?³A₂ and the 3a₁ → d_x2?y2 nature of the state r?³B₁ are confirmed. © 2012 Wiley Periodicals, Inc.     

Potential energy curves of several excited states of the Ne2* excimer: Assignment of the transient absorption spectra of the excimer

Most of the excited states of Ne₂, which are correlated with the Rydberg state transitions 2p → 3s, 3p, and 4s of Ne, are studied by ab initio CI calculations. Two transient absorption spectra from the lowest excimer state Σ_u⁺ recently observed by Arai et al., are discussed on the basis of calculated potential energy curves. Possible assignments are presented. The calculated transition energies are in good agreement with the observed ones.     

Synchrotron radiation induced photoionization and photodissociation of carbon monoxide in the 14–35 eV region

Carbon monoxide has been excited with monochromatic synchrotron radiation in the 14–35 eV range using the Swedish synchrotron facility MAX in Lund. The decay products were studied in various detection channels such as formed CO⁺ and C⁺ ions using mass spectroscopy and visible or VUV fluorescence using photon detection. A rich line structure is observed which is attributed to CO Rydberg series converging to theX,A,B,D,C andE states in CO⁺. While a great number of these lines are already known, some of them are classified here for the first time. The combination of information from the fluorescence spectra and the mass spectra contribute important information concerning the autoionization and predissociation of these various Rydberg series.     

Confocal laser microspectroscopic Rabi-flopping study of an iron oxide emitter surface used for Rydberg matter generation

Rydberg matter (RM) is a novel metal-like material in the form of electronically excited clusters of atoms (e.g. K and H) or molecules (e.g. H(2)). It is used as the inverted laser medium for IR in the RM laser. RM has recently been formed in its lowest state, which is proposed to be metallic hydrogen [Energy and Fuels 19 (2005) 2235]. An emitter material (K-doped iron oxide catalyst) that forms RM is studied by a specialized spectroscopic method, needed to detect the Rydberg states on the emitter surface. The spectroscopic method is phase-delay Rabi-flopping; it gives spectra from the time delay due to the periodic motion of the optical nutation vector. The formation of Rydberg species in the form of complexes K*-M (M a general small molecule) and (K-M)* is studied. So-called avoided transitions in K(+) ions are detected, of the same type as observed as transitions in the RM laser by stimulated emission. The formation and detection of Rydberg complexes containing H and H(2) is of great interest for metallic hydrogen production. Complexes with M=CH(2), H(2)O (or OH), CHO, H(2) and M'H are observed. Avoided transitions in RM clusters K(N)(*) are also identified. The identification of H containing Rydberg complexes on the surface indicates that metallic hydrogen is formed by the same cluster desorption route as other RM clusters.     

High resolution spectroscopy of small metal clusters

The optical absorption spectrum of small lithium clusters has been measured up to Li₈. In Li₃ high resolution Two Photon Ionization (TPI) spectra have been recorded allowing us to determine the geometry and potential surfaces of the ground and excited states. In larger clusters, the excited states are dissociative and the absorption spectra have been obtained by Depletion Spectroscopy. Vibronic resolution is still achieved in Li₄, but not in larger clusters. The measured spectra exhibit a rather small number of transitions to electronically excited states. In Li₇, only one intense band is observed in the blue region, while in Li₈, an intense band is also observed in the blue region and a much weaker band in the red region. All the obtained results are in very good agreement with the ab initio calculation of Bonacic-Koutecky et al. This demonstrates that molecular effects are always present in these small clusters. The semi-classical models of surface plasma resonances are also discussed.     

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.     

Photoionization,Structures, and Energetics of Na-Doped Formic Acid–Water Clusters

The influence of formic acid on water cluster aggregation has been investigated experimentally by mass spectrometry and tunable UV laser ionization applied to Na-doped clusters formed in the supersonic expansion of water vapors seeded with formic acid (FA) as well as theoretically using high level quantum chemistry methods. The mass spectra of Na−FA(H₂O)_n clusters show an enlarging of mass distribution toward heavier clusters with respect to the Na−(H₂O)_n clusters, suggesting similar mass distribution in neutral clusters and an influence of formic acid in water aggregation. Density functional theory and coupled-cluster type (DLPNO-CCSD(T)) calculations have been used to calculate structures and energetics of neutral and ionized Na−FA(H₂O)_n as well as neutral FA(H₂O)_n. Na-doped clusters are characterized by very stable geometries. The theoretical adiabatic ionization potential values match pretty well the measured appearance energies and the calculated first six electronic excited states show Rydberg-type characters, indicating possible autoionization contributions in the mass spectra. Finally, theoretical calculations on neutral FA(H₂O)_n clusters show the possibility of similarly stable structures in small clusters containing up to n=4–5 water molecules, where FA interacts significantly with waters. This suggests that FA can compete with water molecules in the starting stage of the aggregation process, by forming stable nucleation seed.