bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared spectroscopy and a
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o theory of the structural isomers of CO2–HCN
Authors: Dayton D. C. , Pedersen L. G. , Miller R. E.
Published: July 2002

Infrared spectra have been obtained for the liner and T-shaped isomers of CO2–HCN using the optothermal detection method. These spectra correspond to the intramolecular C–H stretching vibration in each isomer. The infrared results are consistent with the structures determined previously from microwave spectroscopy and provide additional data that is helpful in making meaningful comparisons with theory. Ab initio calculations have also been carried out for this system using three different basis sets. The agreement between the experimental and calculated structures is good for all three basis sets, while the vibrational frequency shifts (scaled to the monomer) and the intermolecular stretching force constants are much more basis set dependent. Nevertheless, the overall agreement between experiment and ab initio theory is very good.
Predissociation of the Cs2 C 1Πu state
Authors: Baba Masaaki , Nakahori Tadaki , Iida Tetsuya , Katô Hajime
Published: July 2002

By scanning the frequency of a single-mode dye laser crossed to a molecular beam of Cs2, we measured the excitation spectra of the C 1∏u–X 1∑+g transition by detecting selectively the molecular fluorescence and the emission from the dissociated Cs(62P3/2) atoms. Dependence of the predissociation on each vibrational and rotational level C 1∏u (v,J) is studied by comparing the intensities of molecular fluorescence and atomic emission. This predissociation is found to depend strongly on the vibrational quantum number v but weakly on the rotational quantum number J, and to occur most strongly around the v=3 level. The Franck–Condon factors between the RKR potential curve of the C 1∏u state and several repulsive potential curves are calculated, and are compared with the observed predissociation rates. The potential curve of the (2)3∑+u state, which is expected to be repulsive and to cause the predissociation through the spin–orbit interaction, is estimated to cross the potential curve of the C 1∏u state between the left turning points of v=1 and v=0 levels.
Comment on: The torsional potential function of dimethylaminobenzonitrile and related compounds in their S1 states
Authors: Gordon Robert D.
Published: July 2002

An S1 ring-N(CH3)2 torsional potential function with V2≂3700 and V4≂−1450 cm−1 is deduced from the published spectrum [Grassian et al., J. Chem. Phys. 90, 3994 (1989)] of 4-N,N-dimethylaminobenzonitrile. The equilibrium conformation is twisted by 25°, and there are barriers of 185 and 3900 cm−1 at the planar and perpendicular conformations. Similar results are obtained for the (CD3)2 derivative, and for N,N-dimethylaniline, 3-N,N-dimethylaminobenzonitrile, and 4-(trifluoromethyl)-N,N-dimethylaniline.
Rotational heating and cooling during the evaporation of atoms from excited clusters
Authors: Stace A. J.
Published: July 2002

A model based on phase space theory has been used to examine the effect that multiple fragmentations from excited, weakly bound cluster ions have on the final rotational temperatures of the reaction products. It is predicted that small clusters, such as Ar+2 and Ar+3, could emerge from a multiple reaction sequence with comparatively high rotational temperatures. In contrast, large clusters, e.g., Ar+40, experience slight rotational cooling when they undergo ≂15 fragmentation steps. In each case, these results can be rationalized in terms of the relative magnitudes of the rotational and orbital angular momenta at each reaction step. Recent experimental observations on cluster ions are discussed in the light of predictions from the model.
Jahn–Teller analysis of the Na3 A state
Authors: Dugourd Ph. , Chevaleyre J. , Perrot J. P. , Broyer M.
Published: July 2002

The observation of some new bands assigned to the Na3 X–A system has allowed a rather complete theoretical treatment of the A electronic state. It exhibits large quadratic Jahn–Teller interaction giving rise for the lower levels to a localization in a hindered pseudorotation well. The band positions and intensities are in agreement with the values Es=1847 cm−1 and Eloc=196 cm−1, respectively for the stabilization and pseudorotation barrier energies.
Dissociation dynamics: Measurements of decay fractions of metastable ammonia cluster ions
Authors: Wei S. , Tzeng W. B. , Castleman A. W.
Published: July 2002

The decay fractions of metastable ammonia cluster ions which undergo unimolecular (evaporative) dissociation in a time window of 1–40 μs were measured by using a reflection time-of-flight mass spectrometer. Corrections concerning instrumental artifacts and ion trajectory of parents and daughters are made to imporve the precision of the measurements. The data are used to derive the Gspann parameter and heat capacity of clusters as described in evaporative ensemble model of metastable dissociation. Using the dissociation fractions measured in the present studies, in conjunction with kinetic energy release values previously measured in our laboratory, we apply Klots’ evaporative ensemble model to obtain binding energies of ammonia cluster ions (NH3)nH+, 4≤n≤17. The deduced binding energy values are found to be in very good agreement with both thermochemical data and Engelking’s modified statistical theory.
Photoionization of HBr and DBr near threshold
Authors: Ruscic B. , Berkowitz J.
Published: July 2002

Photoionization is observed in HBr (at 300 K) below the adiabatic threshold. The photoion yield curve has structure, and is independent of both pressure and electric field over a large range. The peaks can be simulated rather well by a model which assumes rotational autoionization, with ΔN≂−4. This model does not exclude concomitant processes with ΔN=−1,−2,−3. A formal theory is also presented, which describes ΔN=−4 as occurring through successive quadrupole transitions, in second-order perturbation theory. A tentative conclusion is drawn, based on preliminary studies of other molecules, that a type of rotational autoionization can occur in heteronuclear diatomic molecules without an electric field, and in homonuclear diatomic molecules with such a field. The photoionization of DBr has been studied with similar conditions. A corresponding simulation is in good agreement with the observed structure below the adiabatic threshold. In addition, one peak in a triad observed in HBr above threshold, and predicted by an MQDT calculation to be absent in DBr, is still observed.
Structure of the H2O–(CO2)2 trimer
Authors: Gutowsky H. S. , Chuang Carl
Published: July 2002

Rotational constants reported previously [J. Chem. Phys. 90, 5964 (1989)] for the C2 asymmetric tops H2O–(CO2)2, D2O–(CO2)2, H218O–(CO2)2 and H2O–(13CO2)2 have been reanalyzed. It is found that the slipped parallel (CO2)2 subunit, instead of remaining planar as in the free dimer, has the inner oxygens rotated away from the H2O by ∼20°. This leads to C–C and c.m. (H2O) to c.m. (CO2)2 distances of 3.497 and 2.370 Å in the clusters.
Instantaneous normal mode analysis as a probe of cluster dynamics
Authors: Adams John E. , Stratt Richard M.
Published: July 2002

We report an analysis of dynamical transitions in small argon clusters based on a study of the vibrational frequencies (photon spectra) of these systems. Even in the liquidlike regime such an analysis can be shown to provide an exact description of the short-time cluster dynamics and represents an alternative to more conventional strategies which concentrate on an enumeration of minimum energy structures. The overall picture of ‘‘melting’’ transitions emerging from this study is one of a series of isomerizations which preserve the short-range structures of the clusters, with the structures linked by these isomerizations sometimes being far from any of the local minima on the potential energy hypersurface. As a part of the analysis, we describe a general method for estimating cluster atom self-diffusion constants from system configurations obtained via either isothermal or isoergic Monte Carlo calculations.
Vibrational autodetachment spectroscopy of Au−6 : Image-charge-bound states of a gold ring
Authors: Taylor K. J. , Jin C. , Conceicao J. , Wang Lai-Sheng , Cheshnovsky O. , Johnson B. R. , Nordlander P. J. , Smalley R. E.
Published: July 2002

Spectral experiments on mass-selected negative cluster ions of gold and silver were performed in the wavelength range near the threshold for one-photon photodetachment of the extra electron. The Au−6 cluster ion displayed a uniquely well resolved spectrum consisting of a progression in a single vibrational mode. Details of this threshold photodetachment spectrum and the associated photoelectron energy distribution suggest an explanation based on autodetachment from totally symmetric vibrational levels of very weakly bound excited electronic state (bound by image charge forces) of the Au−6 cluster in the form of a planar, six-fold symmetric, gold ring.
Cohesive energies of K+n 5<n<200 from photoevaporation experiments
Authors: Bréchignac C. , Cahuzac Ph. , Carlier F. , de Frutos M. , Leygnier J.
Published: July 2002

Evaporative cooling of internal energy rich potassium cluster ions K+n (5<n<200) is investigated within two well defined but quite different time windows. One of the time windows starts 1 μs after the photoexcitation of the cluster ions isolates one step in the evaporative cooling cascade. The experimental technique insures the complete determination of the dissociation channels. Tandem time-of-flight mass spectroscopy measures the relative rate of competing dissociation channels from ion fragmentation patterns. The corresponding neutral fragments are unambiguously determined after the reionization. Values for the dissociation energies of K+n (up to n=25) have been deduced from the unimolecular dissociation rates using statistical methods. These values are compared to Hückel calculations. The second time window starting just after the reexcitation of mass selected K+n is used to follow the steps of the photoinduced sequential evaporation from ‘‘hot’’ clusters. The photofragmentation patterns for several photon energies give the atomization energies of ionized clusters up to n=200. Their evolution vs 1/R is compared to the droplet model.
Surface scattering of NO from graphite: A statistical description of energy distributions
Authors: Nyman Gunnar , Holmlid Leif , Pettersson Jan B. C.
Published: July 2002

In the present theoretical study, inelastic scattering of NO from graphite surfaces is analyzed with a statistical model. The results are in good agreement with previous classical trajectory calculations by Pettersson et al. (1988). Angular distributions and the ‘‘rotational cooling’’ effect found in experiments published by Frenckel et al. (1982), Segner et al. (1983), and Häger and Walther (1984) are successfully reproduced. The model describes a small part of the graphite surface together with a scattering diatom as a collision complex, which decomposes in a unimolecular fashion. The surface is assumed to be flat, whereby the diatom angular momentum component along the surface normal and the linear momentum parallel to the surface are conserved. Otherwise the diatom translation and rotation are allowed to exchange energy with the surface, which is characterized by a set of harmonic oscillators. The experimentally observed ‘‘rotational cooling’’ effect is clearly demonstrated to be due to the conservation of the normal component of the angular momentum. The surface oscillator mass and the number of surface oscillators are treated as parameters. The results indicate that on the average one to three surface atoms are directly involved in each molecule-surface collision. ‘‘Rotational rainbow’’-like distributions are observed at high total energies, even though the simulations are purely statistical with no dynamic effect included.
An energy functional of electron-pair density
Authors: Koga Toshikatsu
Published: July 2002

The electron-pair (or intracule) density is the probability density function for an interelectronic vector and is intimately related to the electron correlation in many-electron systems. Based on the local scaling method, a theory is presented for the direct variational determination of the electron-pair density. Illustrative applications are given for the ground state of the helium atom. Simple electron-pair density functions are reported which compare quantitatively with the exact density.
Molecular photo cross sections with the LCGTO–Xα method using Stieltjes imaging
Authors: Görling A. , Rösch N.
Published: July 2002

A method for calculating and symmetry analyzing total molecular photoionization cross sections is presented. The technique is based on the LCGTO–Xα method and employs Stieltjes imaging. It allows applications to molecular systems comparable in size to those treated so far with the continuum multiple-scattering Xα method, but avoids the pitfalls of the muffin-tin approximation to the electronic potential. Photo cross sections for valence ionization of CO are found in good agreement with experiment and with previous calculations. From a final state symmetry analysis for the 1π level, the absence of kσ* shape resonance which appears in the 4σ and the 5σ ionization channels is attributed to small transition moments. This is in contrast to a previous treatment where this difference has been rationalized as caused by a channel dependent final state potential. The photoionization cross sections for the four highest valence orbitals of benzene were calculated in better agreement with experiment than found in a previous Xα–SW treatment. The improvement is especially significant for the 1e1g(π) highest occupied molecular orbital where at least part of the experimentally observed structures are attributed to shape resonances. Some of the observed resonance features in the valence orbital photo cross sections of benzene were identified with resonances found in carbon K-shell ionization.
Photodissociation of adsorbed Mo(CO)6 induced by direct photoexcitation and hot electron attachment. I. Surface chemistry
Authors: Ying Z. C. , Ho W.
Published: July 2002

The adsorption and photodissociation of Mo(CO)6 on potassium-free and potassium-preadsorbed Cu(111) and Si(111)7×7 have been studied under ultrahigh vacuum conditions using vibrational spectroscopy and mass spectrometry. It has been observed that Mo(CO)6 adsorbs molecularly on potassium-free Cu(111) and Si(111)7×7 at 85 K and, upon heating, desorbs at 200 K. In the case of Cu(111), heating also leads to thermal dissociation of a fraction of Mo(CO)6 at ∼150 K. The dissociation channel competes favorably with the molecular desorption channel at low Mo(CO)6 exposures. On potassium-preadsorbed Cu(111) and Si(111)7×7 at 85 K, Mo(CO)6 adsorbs in part molecularly and in part dissociatively. The extent of dissociation depends on the K coverage; a high K coverage results in large degree of dissociation. The thermal desorption temperature for the molecularly adsorbed Mo(CO)6 increases to 210 K on the potassium-preadsorbed surfaces. Adsorbed Mo(CO)6 molecules photodissociate nonthermally into CO and carbonyl fragments. The product CO desorbs under irradiation. Photodissociation occurs on the K-free surfaces only under ultraviolet (UV) irradiation. With coadsorbed potassium, however, the photoyield increases substantially in the UV and extends to the visible and infrared (IR) regions. The carbonyl fragments which are present on the K-preadsorbed surfaces before irradiation are found to have a negligible contribution to the CO desorption signal. The photoactive species is identified to be the molecularly adsorbed Mo(CO)6 .
Electronic structures of the negative ions Si−2 –Si−10: Electron affinities of small silicon clusters
Authors: Raghavachari Krishnan , McMichael Rohlfing Celeste
Published: July 2002

Accurate ab initio calculations have been performed to investigate the structures and energies of the negative ions of Si2–Si10. The effects of polarization functions, diffuse functions, and electron correlation have been included in these calculations. In most cases, there is a good correspondence between the ground state structures of the negative ions and those of the corresponding neutral species. Adiabatic electron affinities are computed and compared with recent experimental measurements. Si3, Si5, Si8, and Si9 are found to have electron affinities which are larger than their neighbors. This result is interpreted using our previous calculations on the low-lying states of the corresponding neutral species.
Absorption spectra of size-selected solvated metal cations: Electronic states, symmetries, and orbitals in Sr+(NH3)1,2 and Sr+(H2O)1,2
Authors: Shen M. H. , Farrar J. M.
Published: July 2002

This paper presents photodissociation spectra for the solvated metal ion clusters Sr+(NH3)1,2 and Sr+(H2O)1,2 from 420 to 740 nm in the visible region of the spectrum. The spectra have a banded structure, corresponding to transitions from ground electronic states based upon the 2S configuration of the Sr+ ion to excited states based primarily upon p-orbitals of the excited Sr+. The photodissociation cross sections are large, ∼10−17–10−16 cm2. For the same solvent, spectral band positions are only weakly dependent upon the degree of solvation. We show that a dramatic reduction in intensity of the second excited state band in the Sr+(NH3)2 spectrum suggests that this state has strong atomic ion d-orbital parentage and that the molecule is centrosymmetric. Photodissociation of the H2O solvated species proceeds through three excited electronic states corresponding principally to three different orientations of the metal p orbitals with respect to solvent symmetry axis. Absorption band positions for Sr+(H2O)2 are shifted slightly from those of Sr+(H2O) and the presence of a substantial unstructured continuum appears in the doubly solvated ion. The absorption spectra for the Sr+(H2O)1,2 species are significantly blue-shifted and narrowed relative to those of Sr+(NH3)1,2, an observation that is understood through simple molecular orbital diagrams incorporating the fact that the ionization potential of H2O is 2.4 eV larger than that of NH3.
Ultra-violet-laser-induced chemiluminescence of NaCd and NaHg excimers
Authors: Windholz L. , Musso M. , Pichler G. , Hess B.
Published: July 2002

A single line UV Ar++ laser has been used for the photochemical production of NaCd and NaHg excimers, detected by their characteristic bound–free emission in the blue spectral region. Selected laser lines excited specific levels in the C 1Πu electronic state of the Na2 molecule. The chemical reaction of the excited sodium dimer with Cd or Hg atoms produced NaCd and NaHg excimers. We suggest a simple model for the explanation of the observed spectra, based on recent ab initio theoretical calculations.
Ammonia chemisorption studies on silicon cluster ions
Authors: Alford J. M. , Laaksonen R. T. , Smalley R. E.
Published: July 2002

Silicon clusters in the size range from 5 to 66 atoms were generated by laser vaporization in a supersonic nozzle and injected into the ion trap of a specially-designed Fourier transform ion cyclotron resonance apparatus. On the positively charged clusters ammonia chemisorption reaction rates were found to vary by over three orders of magnitude as a function of cluster size, with clusters of 21, 25, 33, 39, and 45 atoms being particularly unreactive, and cluster 43 being the most reactive. For the negative cluster ions, 43 was the only cluster found to react substantially. Although the reaction behavior of many clusters clearly indicated that several structural isomers were present with different reaction rates, the strikingly low net reactivity of such clusters as 39 and 45 provides evidence that they have effectively crystallized into a single specially stable form.
The binding energies of Cu+–(H2O)n and Cu+–(NH3)n (n=1–4)
Authors: Bauschlicher Charles W. , Langhoff Stephen R. , Partridge Harry
Published: July 2002

The successive binding energies of up to four H2O and NH3 ligands to Cu+ are computed at the self-consistent-field and modified coupled-pair functional levels. The most stable structures are those where all ligands are equivalent. Replacing Cu+ by a point charge gives binding energies that are in good agreement with ab initio and experimental results, and is consistent with bonding that is largely charge dipole in nature. About two-thirds of the large reduction in ligand binding energy between the second and third ligand is due to ligand–ligand repulsion, while one-third is due to increased metal–ligand repulsion resulting from a loss of sdσ hybridization. The first and second ligand binding energies increase substantially at the correlated level due to an improved description of sdσ hybridization.
Infrared laser absorption spectroscopy of the ν4(σu) fundamental and associated ν11(πu) hot band of C7: Evidence for alternating rigidity in linear carbon clusters
Authors: Heath J. R. , Saykally R. J.
Published: July 2002

The first characterization of the bending potential of the C7 cluster is reported via the observation of the v=11 and v=20 levels of the ν11(πu) bend as hot bands associated with the ν4(σu) antisymmetric stretch fundamental. The lower state hot band rotational constants are measured to be 1004.4(1.3) and 1123.6(9.0) MHz, constituting a 9.3% and 22% increase over the ground state rotational constant [918.89(41) MHz]. These large increases are strong evidence for extremely large amplitude, anharmonic bending modes in this cluster. In addition, quartic and sextic centrifugal distortion constants determined for the ground and ν4=1 states are found to be anomalously large and negative, evidencing strong perturbations between stretching and bending modes.
Theoretical study of the electronic spectrum of CHF3
Authors: Larrieu C. , Chaillet M. , Dargelos A.
Published: July 2002

A b initio configuration-interaction (CI) calculations for the first electronic states and for the first six ionization potentials of trifluoromethane are reported. The UV spectrum is analyzed and the nature of the Rydberg transition is discussed in terms of the analysis of calculated charge transfer of each state. It is clearly seen that the distinction among type s, p, or d Rydberg states is difficult to establish and that the more intense broadband (B region) results from the overlapping of transition with different natures and intensities.
Elucidating the origin of magic numbers: Trends in the relative binding energies of xenon cluster ions and their implications
Authors: Wei S. , Shi Z. , Castleman A. W.
Published: July 2002

Metastable decay fractions of Xen+, n=5–39, are measured using a reflectron time-of-flight mass spectrometry technique. Employing these data, the relative binding energies of Xen+, n=12–39, are deduced by applying the latest evaporative ensemble model. An excellent correlation is found between the relative binding energies and the intensity anomalies observed in the mass spectrum. Importantly, however, are findings that magic numbers of size n are related to the ratio of the cluster-ion band energies ΔEn/ΔEn+1, and hence are not only influenced by the bonding of this size, but also of n+1 and even n+2! Our results show that magic numbers in the mass spectra alone do not conclusively lead to knowledge of the stabilities and structures of the cluster ions, but consideration of the relative bond energies which can be derived from the new approach are required.
The effect of reagent electronic energy on the dynamics of chemical reactions: A high-resolution crossed beam study of O(3P,1D)+H2S
Authors: Balucani N. , Beneventi L. , Casavecchia P. , Stranges D. , Volpi G. G.
Published: July 2002

Crossed beam reactive scattering studies of the H displacement reaction of both ground 3P and excited 1D oxygen atoms with H2S show that the reaction dynamics changes dramatically upon electronic excitation: while the reaction of O(3P) is direct, that of O(1D) proceeds via a long-lived complex.
Copper clusters: The interplay between electronic and geometrical structure
Authors: Winter B. J. , Parks E. K. , Riley S. J.
Published: July 2002

Copper clusters in the 50- to 100-atom size range are found to exhibit electronic shell structure as well as icosahedral geometry. Clusters corresponding to filled shells have minimum intensity in near-threshold photoionization mass spectra, implying that they have locally higher ionization potentials than other cluster sizes. The chemical stability of these clusters is illustrated by a reduced reactivity towards O2. Cluster geometry is probed via the equilibrium reactions with H2O: Clusters having one copper atom more than closed icosahedral subshells show an enhanced binding of water. The relative importance of electronic and geometrical structure in determining cluster chemical properties is discussed.
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o potential energy surfaces of Ar–H2O and Ar–D2O
Authors: Bulski M. , Wormer P. E. S. , van der Avoird A.
Published: July 2002

We present an ab initio potential energy surface for the van der Waals system argon–water. The points on the surface are computed as a sum of Heitler–London short range repulsion, damped dispersion, and damped induction. Damping is done in the manner first proposed by Tang and Toennies. We give the surface analytically in the form of a spherical harmonic expansion through l=7. The expansion coefficients are represented by functions depending on the distance between the centers of mass of the monomers. We also present an Ar–D2O potential obtained from the Ar–H2O potential by translating the center of mass of the water molecule. An analytic formula for the translation of polarizabilities is derived and applied to the computation of the long range energy of Ar–D2O. The short range part of the energy is translated numerically. Finally, the potential is checked by comparison of computed interaction virial coefficients with experimental data.
A mass formula for 4He clusters
Authors: Balbás L. C. , Mañanes A. , Membrado M. , Pacheco A. F. , Sañudo J.
Published: July 2002

An analytic expression for the total energy of 4He clusters composed of N atoms is obtained by means of a variational solution of the energy density functional. The energy is calculated as an expansion in decreasing powers of the cluster radius, R∝N1/3. Contributions of volume (R3), surface (R2), curvature (R), constant (R0), (1/R), and (1/R2) are clearly separated in the formula. Chemical potentials, fusion and fission potentials, surface thickness, and unit radii are also obtained.
Mass selected resonance enhanced multiphoton ionization spectroscopy of aniline–Arn (n=3,4,5, ...) van der Waals complexes
Authors: Bieske Evan J. , Uichanco Angelo S. , Rainbird Mark W. , Knight Alan E. W.
Published: July 2002

The origin region of the S1←S0 transitions of the aniline–Ar3, aniline–Ar44, and aniline–Ar5 molecules have been measured using mass selected resonance enhanced, multiphoton ionization (REMPI) spectroscopy. The aniline–Ar3 spectrum exhibits two distinct groups of peaks. The more prominent group displays a regular vibrational progression, with five obvious members and a spacing of ∼16 cm−1. Vibrational structure in the other group is less distinctive. On the basis of cluster potential calculations described in this paper, we believe that two stable aniline–(argon)3 isomers exist in the supersonic expansion and that the two groups of peaks correspond to absorption by these two isomers. Spectra recorded at masses corresponding to aniline–(argon)4 and aniline–(argon)5 display broadened structure that probably reflects contributions from larger aniline–(argon)n clusters which fragment upon ionization. There is, however, some evidence for a progression with a spacing of ∼16 cm−1 in the aniline–(argon)4 spectrum. Dispersed fluorescence spectra from relatively small aniline–Arn clusters (4<n<10) indicate that vibrational redistribution from Franck–Condon active van der Waals modes occurs with rates of at least 5×109 s−1.
Grid representation of rotating triatomics
Authors: Leforestier Claude
Published: July 2002

A grid formulation is presented for the body-fixed (BF) motion of a rotating triatomic molecule. The BF component of the wave function, described in terms of Jacobi coordinates, is discretized on a {Ri×rj×θα} grid. By use of the generalized discrete variable representation (DVR) of Light, Hamilton, and Lill [J. Chem. Phys. 82, 1400 (1985)] one can employ the same θ grid for the different Ω components of the wave function, Ω corresponding to the projection of the total angular momentum J onto the z BF axis. Such a unique grid definition allows one to define adiabatic states, with respect to the θ coordinate, independent of the Ω value considered. These states have been directly computed by means of a distributed 2D DVR, sampling only the relevant points in configuration space. Further reduction of the rovibrational basis set was achieved by defining new adiabatic states, with respect to the Ω component. This formation is applied to the calculation of bound rovibrational states of the HCN molecule for the J=2 value.
The NaLi 1 1Σ+(X) electronic ground-state dissociation limit
Authors: Fellows C. E.
Published: July 2002

The NaLi 1 1Σ+(X) electronic ground state has been studied by Fourier transform spectroscopy and laser-induced fluorescence up to near the dissociation limit. The fluorescence has been induced by Ar+, Kr+ and dye (DCM and rhodamine 6G) laser lines. Fluorescence spectra have been observed up to v″=43 and accurate molecular constants have been calculated for the electronic ground state after reducing the wave numbers of 6417 assigned lines in a least-squares fit. With the molecular constants an inverted-perturbation-approach potential curve has been calculated. A value for the dissociation energy of De=7105.5±1.0 cm−1 has been obtained by fitting the energy levels with high vibrational quantum numbers to a multipolar expansion in the inverse power of the internuclear distance. The multipolar expansion coefficients C6, C8, and C10 have been obtained, showing a good agreement with theoretical values calculated earlier. In the fluorescence spectrum induced by the 476.5 nm Ar+ laser line, extra fluorescence series have been observed. The possible collisional energy transfer in the 1 1Π(B) electronic state at the origin of these lines is discussed.
Determination of the Na–Kr interaction potential in the XΣ and AΠ state by laser spectroscopy
Authors: Brühl Rüdiger , Kapetanakis Joannis , Zimmermann Dieter
Published: July 2002

We have extended our previous laser spectroscopic investigation of the AΠ–XΣ transition of the van der Waals molecule NaKr84. Our experimental data consist now of about 1300 absorption lines and of the spectral intensity distribution of the fluorescence light. Spectroscopic parameters have been derived for the vibrational states 0,...,2 of the XΣ state and 7,...,14 of the AΠ state. The interatomic potentials of the XΣ and the AΠ states have been determined in a fully quantum-mechanical approach using analytical HFD or Tang–Toennies functions. For the equilibrium distance and the well depth we obtain 4.918(4) Å, 68.4(5) cm−1 for XΣ and 3.03(4) Å, 3.05(4) Å and 795(25) cm−1, 760(20) cm−1 for AΠ1/2 and AΠ3/2, respectively.
Calculations of the binding energies and structures of sodium chloride clusters and cluster ions
Authors: Phillips N. G. , Conover C. W. S. , Bloomfield L. A.
Published: July 2002

We have calculated the geometries and binding energies for the most tightly bound isomers of (NaCl)n, n=2 to 15, and (NaCl)nNa+ and (NaCl)nCl−, n=2 to 14. In this paper, we discuss the methods used to obtain these geometries and binding energies and compare our results with experimental observations and previous calculations. We have also determined the energies required to remove NaCl molecules adiabatically from clusters and have calculated relative decay rates for evaporative dissociation at various temperatures.
The ground and excited states of C60M and C60M+ (M=O, F, K, Ca, Mn, Cs, Ba, La, Eu, U)
Authors: Chang Agnes H. H. , Ermler Walter C. , Pitzer Russell M.
Published: July 2002

Restricted Hartree–Fock ab initio calculations using relativistic core potentials were performed on C60M (M=O, F, K, Ca, Mn, Cs, Ba, La, Eu, U) complexes with M as the central atom in the C60 truncated icosahedron. The icosahedral symmetry was used to great advantage in the calculations. The ground and excited states of both neutral complexes and their positive ions were studied, and the population analyses for the ground states of the complexes were obtained. The C60 cage accepts one or two electrons from electropositive elements in a formal sense, but the actual charge is usually less. Electrons in large-radius s orbitals on the central atom tend to move outward to the carbon cage or inward to smaller-radius d orbitals on the central atom. For the larger central atoms, ionization occurs from a cage orbital so that the ionization potentials of these complexes are almost constant.
Aluminum cluster reactions
Authors: Leuchtner R. E. , Harms A. C. , Castleman A. W.
Published: July 2002

Aluminum clusters, both anion and cation, are produced using laser vaporization and reacted under thermal conditions with oxygen in a flow tube reactor. An etching reaction is observed and bimolecular rate constants are reported for Al+n, n=1–33, and Al−n, n=5–37. For certain clusters, namely Al+7, Al−13, and Al−23, no apparent reactivity is observed (they are found to be produced from larger species). Interestingly, these correspond to predicted jellium shell closings with 20, 40, and 70 electrons, respectively. Besides these exceptions, and a small odd/even alternation in reaction rates, the overall reactivity is relatively insensitive to cluster size, and is found to range between about 1 × 10−12 and 5 × 10−12 cm3/s.
Monte Carlo simulation of (H2O)8: Evidence for a low-energy S4 structure and characterization of the solid ↔ liquid transition
Authors: Tsai C. J. , Jordan K. D.
Published: July 2002

It is found that (H2O)8 possesses two nearly isoenergetic structures, one with D2d and the other with S4 symmetry, and that the (H2O)8 cluster undergoes a transition between a ‘‘solidlike’’ phase (dominated by the S4 and D2d structures) and ‘‘liquidlike’’ phase at a temperature near 119 K.
Photoelectron spectroscopy of negatively charged bismuth clusters: Bi−2, Bi−3, and Bi−4
Authors: Polak Mark L. , Ho Joe , Gerber Gustav , Lineberger W. C.
Published: July 2002

We have recorded the 351 nm photoelectron spectra of Bi−2, Bi−3, and Bi−4. The spectrum of Bi−2 shows transitions to at least seven electronic states of Bi2 neutral, four of which are observed with vibrational resolution. Term energies, bond lengths, and vibrational frequencies are obtained for the anion ground state and for the first three excited states of Bi2. These results are compared to previous spectroscopic measurements and to the ab initio calculations presented in the accompanying paper. The photoelectron spectrum of Bi−3 reveals some of the electronic structure of Bi3 and the results are discussed in comparison to recent theoretical work. Adiabatic electron affinities are obtained for Bi2 [1.271(8) eV] and for Bi3 [1.60(3) eV]. The electron affinity of Bi4 is estimated from the onset of photodetachment to be 1.05(10) eV.
On the simulation of thermodynamic and structural properties of simple liquids
Authors: Svensson Bo , Åkesson Torbjörn , Woodward Clifford E.
Published: July 2002

This work, which is purely methodological, demonstrates new applications of perturbation methods in computer simulations of simple liquids. Most applications are based on the calculation of bulk and local excess chemical potentials of one or several inserted test particles, using a Widom technique in the canonical ensemble. This gives a powerful tool for obtaining distribution functions, some of which are virtually impossible to determine with other techniques. Results are also presented for single-ion activity coefficients and Donnan potentials. A perturbation approach is used to calculate thermodynamic response functions with respect to particle number, temperature, and volume changes. The applicability is exemplified by studies of hard-sphere fluids, uniform and nonuniform electrolyte solutions within the primitive model, and screened Coulomb systems.
Multiphoton excitation, ionization, and dissociation decay dynamics of small clusters of niobium, tantalum, and tungsten: Time-resolved thermionic emission
Authors: Amrein Andreas , Simpson Richard , Hackett Peter
Published: July 2002

The ionization dynamics of transition metal clusters have been investigated using time-of-flight mass and electron spectroscopy following single-photon (220 nm) and two-photon (351, 308, and 248 nm) excitation by pulsed laser light. At 220 nm, the ionization is direct and only prompt photoelectrons are produced. At 308 nm, delayed photoelectrons are produced. In consequence of this delayed ionization process, the time-of-flight mass spectrum peaks show exponential tails (decay time 0.67, 0.40, and 1.54 μs for Nb+7, Ta+7, and W+7, respectively). The decay time is shown to have an explicit dependence upon the cluster nuclearity and the laser wavelength.

Experiments, in which the acceleration voltage of the time-of-flight spectrometer is pulsed on after the photoionization laser pulse, reveal that the precursor to the delayed ion signals is a neutral molecule, further evidence for a delayed ionization process. Similar effects are also seen for transition metal carbide clusters. Clusters of the same nuclearity have approximately equal decay times independent of the number of carbon atoms in the cluster. Transition metal oxide clusters do not give a two-photon ionization signal. These observations are explained using a model for the two-photon excitation, dissociation, and ionization dynamics. The central feature of this model is that following single photon excitation of an electronic transition below the ionization potential, there is rapid internal conversion among all vibronic states. The absorption of a second photon then creates a vibrationally excited cluster which contains internal energy greater than the ionization potential, but which can only ionize by a nonadiabatic process. This delayed ionization process occurs in competition with dissociation. As clusters of niobium, tantalum, and tungsten and their carbides are very strongly bound, the dissociation rate is slow and the delayed ionization may be observed. Oxidized clusters are expected to be less strongly bound as the diatomic transition metal oxide provides an excellent leaving group; in consequence, no delayed ionization is observed for partially oxidized clusters. The rates for dissociation and ionization of the bare metal clusters have been calculated within the framework of a generalized statistical theory for cluster processes. These rates are in general agreement with the measured decay times. In addition, the rates have been estimated by a procedure which uses tabulated thermodynamic parameters for the bulk elemental materials and makes an explicit correction for the size dependence. Once again, a reasonable agreement is obtained. These results provide the first experimental observation of a delayed ionization process for a neutral polyatomic molecular system. In analogy with materials properties, they also represent the first experimental observation of time-resolved thermionic emission.
Photoelectron spectroscopy of iodine anion solvated in water clusters
Authors: Markovich Gil , Giniger Rina , Levin Menachem , Cheshnovsky Ori
Published: July 2002

We have measured the photoelectron spectra of clusters of I- solvated in water up to fifteen water molecules. The vertical binding energy of the electron increases with cluster size and levels off in clusters containing more than six water molecules. These results strongly indicate that the first solvation layer around the ion consists of six water molecules. This picture is quantitatively consistent with the photoelectron spectroscopy result of I- solvated in bulk water.
Excited ionic and neutral fragments produced by dissociation of the N+2* H band
Authors: Samson James A. R. , Chung Y. , Lee E.-M.
Published: July 2002

NI and NII fluorescent radiation has been observed when N2 was irradiated by undispersed synchrotron radiation with an upper energy limit of approximately 200 eV. The excited fragments originate from dissociation of a band of excited ionic states of N2 lying between 34.7 and 44 eV.
Local and nonlocal density functional study of Ni4 and Ni5 clusters. Models for the chemisorption of hydrogen on (111) and (100) nickel surfaces
Authors: Mlynarski P. , Salahub D. R.
Published: July 2002

The results of density functional calculations using the local density approximation and the self-consistent implementation of density gradient type nonlocal corrections to exchange and correlation are reported for the nickel dimer and for Ni4 and Ni5 clusters. Using these clusters as models for (111) and (100) Ni surfaces the chemisorption energies for atomic hydrogen are also presented. The idea of Siegbahn to prepare the cluster for chemisorption by making a proper excitation to a bonding state has been examined. Using this approach, the chemisorption energy from calculations on these very small nickel clusters agrees very well with the experimental surface data, when nonlocal corrections are included. Chemisorption energies as well as electronic properties of the bare nickel clusters are discussed in the context of local and nonlocal treatments of exchange and correlation.
Theoretical study of the spectroscopy of B2
Authors: Langhoff Stephen R. , Bauschlicher Charles W.
Published: July 2002

The singlet, triplet, and quintet states of B2 below about 45 000 cm−1 have been studied at the multireference configuration-interaction (MRCI) level in a [4s 3p 2d 1f] atomic natural orbital (ANO) Gaussian basis set. Calculations employing a [5s 4p 3d 2f 1g] ANO basis were also performed for the low-lying states, X 3Σ−g, A 3Πu, a 5Σ−u, b1Δg, and c 1Σ+g, to assess the accuracy of the spectroscopic constants determined with the smaller basis and to position the singlet, triplet, and quintet manifolds as accurately as possible. Our best estimate of the Te value for the a 5Σ−u state is 1701 cm−1. A D0 value is computed for the X 3Σ−g state of B2 of 2.78 eV and estimate that D0 is 2.85±0.06 in the complete CI limit. This value is within the error bars of the rather uncertain JANAF value, but is larger than the value of 2.71 eV determined recently using the G1 approach. Einstein coefficients are presented for selected triplet–triplet transitions, and radiative lifetimes for the triplet states to help characterize the optical spectra. Finally the potential energy curves of B2 are compared to those determined in an analogous manner for Al2.
Binary homogeneous nucleation theory for the gas–liquid transition: A nonclassical approach
Authors: Zeng X. C. , Oxtoby D. W.
Published: July 2002

We have employed density functional theory to study gas–liquid nucleation in binary fluids. Effects of surface enrichment and curvature are naturally included in this novel statistical mechanical approach, allowing the classical capillarity approximation to be tested. In this paper we apply the theory to mixtures of Lennard-Jones fluids (modeled on argon and krypton). For these nearly ideal mixtures, the magnitude of nonclassical effects tend to be small, but systematic deviations do appear, with the ratio of the classical to nonclassical rate showing a maximum at intermediate compositions.
Femtosecond time-resolved ionization spectroscopy of ultrafast internal-conversion dynamics in polyatomic molecules: Theory and computational studies
Authors: Seel Matthias , Domcke Wolfgang
Published: July 2002

A framework for the theoretical description of two-pulse time-resolved ionization spectroscopy of ultrafast excited-state dynamics of polyatomic molecules is developed. The radiation–matter interaction as well as intramolecular couplings in the excited-state manifold are treated nonperturbatively by solving the time-dependent Schrödinger equation. The numerical solution is based on a discretization of the ionization continua which becomes particularly efficient for ultrashort laser pulses. With this method converged computations of ionization signals become possible even for complex molecular systems. Computer simulations are performed for a model system representing three-dimensional non-Born–Oppenheimer excited-state dynamics on conically intersecting potential-energy surfaces (the S1 and S2 surfaces of pyrazine). The dependence of the observable time-resolved ionization signals (total ion yield as well as photoelectron spectrum) on the properties of the laser pulses (carrier frequency and pulse duration) is explored. It is demonstrated that ultrafast electronic decay processes as well as coherent vibrational motion in excited states can be monitored by pump–probe ionization with suitable pulses. The dependence of the time-resolved ionization signals on properties of the cation (ionization potentials and potential-energy surfaces) is also discussed.
Electronic structure of KxC60− in the gas phase
Authors: Wang Lai-Sheng , Cheshnovsky O. , Smalley R. E. , Carpenter J. P. , Hwu S. J.
Published: July 2002

The photoelectron spectra of KxC60− (x=1–3) have been studied in the gas phase, and the electron affinities obtained. These were found to decrease linearly with the number of K atoms. The result is consistent with an ionic description of the K–C60 chemical bonding, with each K atom donating its outer 4s electron to the t1u orbital of C60. Vibrational autodetachment from a weakly bound excited electronic state was discovered in KC60−, and a series of three equally spaced peaks were assigned to a progression in the intermolecular K–C60 stretching vibration with a frequency of 140 cm−1.
Spin–orbit configuration-interaction study of valence and Rydberg states of LiBe
Authors: Marino M. M. , Ermler W. C. , Kern C. W. , Bondybey V. E.
Published: July 2002

A b initio spin–orbit full configuration-interaction calculations in the context of relativistic effective core potentials are reported for the weakly bound metal dimer LiBe, a three-valence-electron system. The effects of basis set on the energies of valence and Rydberg states of the cluster are discussed, as are the effects of configuration space selection on the energy of the latter states. Results at the dissociative limit are compared to the experimental atomic spectra. Potential-energy curves and spectroscopic constants are presented for the ground state and fourteen excited states, which includes the Li and Be 2p valence states, the Li 3s, 3p, 3d, and 4s Rydberg states, as well as three low-lying states of the molecular cation.