Search results for "EXCITATION"
showing 10 items of 1290 documents
Calculation of excited-state properties using general coupled-cluster and configuration-interaction models.
2004
Using string-based algorithms excitation energies and analytic first derivatives for excited states have been implemented for general coupled-cluster (CC) models within CC linear-response (LR) theory which is equivalent to the equation-of-motion (EOM) CC approach for these quantities. Transition moments between the ground and excited states are also considered in the framework of linear-response theory. The presented procedures are applicable to both single-reference-type and multireference-type CC wave functions independently of the excitation manifold constituting the cluster operator and the space in which the effective Hamiltonian is diagonalized. The performance of different LR-CC/EOM-…
Large-scale calculations of excitation energies in coupled cluster theory: The singlet excited states of benzene
1996
Algorithms for calculating singlet excitation energies in the coupled cluster singles and doubles (CCSD) model are discussed and an implementation of an atomic-integral direct algorithm is presented. Each excitation energy is calculated at a cost comparable to that of the CCSD ground-state energy. Singlet excitation energies are calculated for benzene using up to 432 basis functions. Basis-set effects of the order of 0.2 eV are observed when the basis is increased from augmented polarized valence double-zeta (aug-cc-pVDZ) to augmented polarized valence triple-zeta (aug-cc-pVTZ) quality. The correlation problem is examined by performing calculations in the hierarchy of coupled cluster models…
Study of a new direct current atmospheric pressure glow discharge in helium
2011
Abstract In this study a new DC-APGD operated in He was developed and characterized. The discharge is operated at 0.9 kV and about 25–35 mA and at a gas flow of 100 ml/min. The source was spectroscopically studied and parameters such as the rotational temperature (Trot), the excitation temperature (Texc), the ionization temperature (Tion) and the electron number density (ne) were determined. The current–voltage characteristic of the source was studied as well. At optimized conditions the discharge operates in the normal region of the current–voltage characteristic. Rotational and excitation temperatures determined with the use of OH band and Fe I lines as thermometric species were of the or…
Photoinduced dissociation of anionic and electron detachment of dianionic gold clusters by use of a laser pointer
2002
Abstract Size-selected anionic and dianionic gold clusters have been stored in a Penning trap and irradiated with the green light of a laser pointer. As examples of special interest, the systems Au 7 − and Au 29 2− have been chosen. In particular, Au 7 − , a small gold cluster with closed electron shell, is observed to decay into Au 6 − and Au 5 − with a decay pathway branching ratio similar to that of Au 9 + . The dianionic cluster Au 29 2− shows electron detachment upon photoexcitation. This observation is in agreement with independent experiments [Stoermer et al., Int. J. Mass Spectrom. 201 (2001) 63], where Au 29 2− is found to be the smallest dianion produced by neutral monomer evapora…
Recent gold cluster studies in a Penning trap
2002
Abstract A progress report is given on the investigation of metal clusters with an ion cyclotron resonance (Penning) trap. The examples are taken from the recent studies on gold clusters. In particular, the monomer and dimer evaporation is monitored as a function of cluster size. For the particular case of Au 7 + this study is expanded to include the energy dependence of the branching ratio. In connection with the sequential decay of Au 8 + the information can be used for a model-free determination of the dissociation energy of Au 8 + . A second line of studies concerns the production, properties and storage behavior of polyanionic gold clusters. Such species have recently been produced by …
Strain Release Chemistry of Photogenerated Small‐Ring Intermediates
2021
Abstract Photochemical processes, such as isomerizations and cycloadditions, have proven to be very useful in the construction of highly strained molecular frameworks. Photoinduced ring strain enables subsequent exergonic reactions which do not require the input of additional chemical energy and provides a variety of attractive synthetic options leading to complex structures. This review covers the progress achieved in the application of sequences combining excitation by ultraviolet light to form strained intermediates, which are further transformed to lower energy products in strain‐release reactions. As ring strain is considerable in small ring systems, photogenerated three‐ and four‐memb…
Optimal design of viscoelastic tuned mass dampers for structures exposed to coloured excitations
2022
Dynamic interaction between primary and secondary structures can alter the response of buildings, bridges and other civil engineering structures to external stressors such as earthquakes and windstorms. TMDs (tuned mass dampers) are a well-known example of passive control devices that exploit this concept. A TMD consists of a secondary mass attached to the primary structure through a linear or nonlinear link. Various formulations exist to optimize the performance of TMDs, depending on the chosen criterion. Typically, the TMD is optimized considering the steady-state amplitude of motion of the primary structure, e.g., when subjected to monochromatic harmonic excitation (H∞ criterion) or whit…
The Hanle effect and level crossing spectroscopy in Rb vapour under strong laser excitation
2003
We measure and simulate numerically the Hanle effect and non-zero field level crossing signals in 85 Rb and 87 Rb atoms in a magnetic field at room temperature. Diode laser radiation from 4 mW cm −2 to 3. 3W cm −2 tuned to the D2 absorption line of each isotope excites atoms into all the excited-state hyperfine levels simultaneously inside the unresolved Doppler profile. Polarization fluorescence detection is used to observe dark and bright resonances, as well as non-zero field level crossing resonances, for several excitation lines. A broad spectral line excitation model is applied to analyse the measured signals. The non-linear Zeeman effect is included in the model for both ground and ex…
Nonlinear Hanle effect in Cs vapor under strong laser excitation
2002
We report results of a theoretical and experimental study of the ground state nonlinear Hanle effect under strong laser excitation. It is shown that besides the well-known zero-magnetic field suppression of absorption on F g = F→F e = F - 1 transitions caused by population trapping, an optical pumping induced enhanced absorption occurs on F g = F→F e = F + 1 transitions for small B-fields. The latter effect becomes more pronounced for high F values. The experiment with atomic vapor of Cs (D2 line, F g = 4) confirms an increase of the spectrally unresolved fluorescence yield at zero magnetic field and 600 mW/cm2 laser intensity by 9% or 42%, when excitation occurs with linearly or circularly…
Communication: Rotational excitation of interstellar heavy water by hydrogen molecules
2010
Cross sections and rate coefficients for low lying rotational transitions in D(2)O induced by para-H(2) collisions are presented for the first time. Calculations have been performed at the close-coupling level with the deuterated variant of the H(2)O-H(2) interaction potential of Valiron et al. [J. Chem. Phys. 129, 134306 (2008)]. Rate coefficients are presented for temperatures between 1 and 30 K and are compared to the corresponding rate coefficients for H(2)O. Significant differences caused by the isotopic substitution are observed and are attributed to both kinematics and intramolecular geometry effects. Astrophysical implications are briefly discussed in view of the very recent detecti…