bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the inversion of atomic scattering data: A new algorithm based on functional sensitivity analysis
Authors: Ho Tak-San , Rabitz Herschel 
Published: July 2002

A new iterative inversion scheme of atomic scattering data within the framework of functional sensitivity analysis is presented. The inversion scheme is based on the first order Fredholm integral equation δσ(θ)=∫∞0K(θ,R)δV(R)R2 dR, K(θ,R)≡δσ(θ)/δV(R), or symbolically, δσ=KδV, which relates infinitesimal functional changes in the elastic differential cross section δσ(θ) and in the underlying interatomic potential δV(R). This equation can be written equivalently, via integration by parts, as δσ(θ)=∫∞0K[n](θ,R) {Rn×δV(n)(R)}R2 dR, or δσ=K[n]{Rn×δV(n)}, under the a priori assumption that {R(2+n)×K[n](θ,R)×δV(n−1) (R)}‖∞R=0=0. Here K[n](θ,R)≡−R−(2+n) ×∫R0K[n−1](θ,R′) R′(1+n)dR′, δV(n)(R) ≡(dn/dRn)δV(R), with n=0,1,2,..., and K[0](θ,R)≡K(θ,R).
A choice of n corresponds to a particular level of additional stabilization inverting the scattering data. By invoking a least squares regularization procedure and singular system analysis, the new indirect inversion scheme solves the linear relation δσ=K[n]{Rn×δV(n)} and results in the approximate solution Rn×δV(n)(R), which can in turn be integrated, n times, to yield the potential correction δV(R). The new algorithm not only makes the inversion more stable and more efficient, but also increases the sensitivity of the large angle scattering data to the repulsive part of the potential, in comparison with a previous method that directly solves the relation δσ=KδV.
For illustration, the model system He–Ne is considered at both low- and high-collision energies, relative to the well depth of the potential. It is found that the indirect method based on the linear relation δσ=K[2]{R2×δV(2)} can more accurately determine both attractive and repulsive parts, including a large section of classically forbidden region, of the potential than its direct counterpart. Furthermore, the indirect method allows for substantial deviations of the initial reference potential from final result, not only in well depth, but in range parameter and asymptotic behavior. Finally, these observations are not significantly dependent on the magnitude of the collision energy.
Infrared absorption spectroscopy of CO2–HX complexes using the CO2 asymmetric stretch chromophore: CO2HF(DF) and CO2HCl(DCl) linear and CO2HBr bent equilibrium geometries
Authors: Sharpe S. W. , Zeng Y. P. , Wittig C. , Beaudet R. A. 
Published: July 2002

Infrared absorption spectra associated with the CO2 asymmetric stretch vibration have been recorded for weakly bonded gas-phase complexes of CO2 with HF, DF, HCl, DCl, and HBr, using tunable diode laser spectroscopy and a pulsed slit expansion (0.15×38 mm2) that provides &gt;20 MHz overall resolution. Results obtained with CO2–HF are in agreement with earlier studies, in which the HF-stretch region near 3900 cm−1 was examined. In both cases, broad linewidths suggest subnanosecond predissociation. With CO2–DF, the natural linewidths are markedly narrower than with CO2–HF (e.g., 28 vs 182 MHz), and this difference is attributed to slower predissociation, possibly implicating resonances in the case of CO2–HF. Both CO2–HF and CO2–DF exhibited overlapping features: simple P and R branches associated with a linear rotor, and P and R branches containing doublets. As in earlier studies, the second feature can be assigned to either a slightly asymmetric rotor with Ka=1, or a hot band involving a low-frequency intermolecular bend mode.
Results obtained with CO2–HCl are in excellent agreement with earlier microwave measurements on the ground vibrational state, and the vibrationally excited state is almost identical to the lower state. Like CO2–DF, linewidths of CO2–HCl and CO2–DCl are much sharper than those of CO2–HF, and in addition, CO2–HCl and CO2–DCl exhibited weak hot bands, as were also evident with CO2–HF and CO2–DF. Upon forming complexes with either HF or HCl, the asymmetric stretch mode of CO2 underwent a blue shift relative to uncomplexed CO2. This can be understood in terms of the nature of the hydrogen bonds, and ab initio calculations are surprisingly good at predicting these shifts. Deuteration of both HF and HCl resulted in further blue shifts of the band origins. These additional shifts are attributed to stronger intermolecular interactions, i.e., deuteration lowers the zero-point energy, and in a highly anharmonic field this results in a more compact average structure. While both HF and HCl complexes exhibit nearly linear geometries,CO2–HBr is asymmetric, with the Br–C symmetry line essentially perpendicular to the CO2 axis, and the H atom probably localized near one of the oxygens. Although the moments of inertia are insensitive to the location of the H atom in CO2–HBr, Bose–Einstein statistics require that odd K″a states are missing for C2v symmetry, as is observed with T-shaped CO2–(rare gas) complexes. However, we observe a full complement of odd and even Ka states, indicating that the H atom is not located symmetrically about the C2v axis on the time scale of the measurement. With CO2–HBr, the low gas-phase acidity of HBr and the high Br-atom polarizability encourage a qualitative change in the geometry relative to CO2–HCl and CO2–HF. This has valuable implications for photoinitiated reactions in such complexes.
A reevaluation of the vaporization behavior of sodium oxide and the bond strengths of NaO and Na2O: Implications for the mass spectrometric analyses of alkali/oxygen systems
Authors: Steinberg Martin , Schofield Keith 
Published: July 2002

There has been a long standing disagreement between our flame experiments, which predict a very stable NaO2 molecule, and Na2O(c) vaporization/mass spectrometric studies of Hildenbrand et al., which imply a weak bond strength from an inability to detect such a species. We have now reanalyzed the vaporization experiments and have identified a possible explanation for this frustrating controversy. It appears that on becoming ionized, NaO+2 fragments to Na+ and O2. As a result, mass 23 reflects p(Na)+p(NaO2). This and the changes to the thermochemical data for NaO2 modifies the earlier ion intensity/vapor pressure calibration. As a result, the previously accepted thermochemical values for NaO and Na2O need to be reduced by 18 and 11 kJ mol−1, respectively. Recommended values now become ΔHf298K (NaO)=87±4, D0(NaO)=266±4, ΔHf298K(Na2O) =−36.0±8 and D0(Na–ONa)=228±8 kJ mol−1. It also appears that the I.P.(NaO2)≤739 kJ mol−1 (7.66 eV).
The reported Clausius–Clapeyron vapor pressure curves are entirely consistent with this suggestion that the congruent vaporization of Na2O(c) is to Na and NaO2 rather than to Na and O2. A reinterpretation utilizing the previous slopes of the I(Na+) or I(O+2) signals leads to an independent measure of −90≥ΔHf298K(NaO2)≥−155 and 194≤D0(Na–O2)≤259 kJ mol−1. These are to be compared with the higher temperature flame determined values of −139±8 and 243±8 kJ mol−1, respectively. Earlier vaporization mass loss measurements of Brewer and Margrave were in approximate agreement with a vaporization to predominantly Na and O2. Analyses now show that the technique is insensitive and congruent vaporization to Na and NaO2 also fits their data. Hildenbrand and Murad measured Na+/O+2 ratios but these appeared to be a factor of 4 smaller than expected for congruency and remained unexplained. By invoking an alternate fragmentation of NaO+2 at higher energies to Na and O+2 (A.P.≊14.6 eV), with a branching ratio of ≥10%, this channel becomes the dominant source of O+2 and the observed Na+/O+2 signal ratios are consistent with congruency. These results have important implications for all mass spectrometric studies of alkali/oxygen mixtures including, for example, also carbonates and nitrates. A reappraisal for these is in order, particularly with reference to derived thermochemical values.
The 846 nm A′ 3Σ−u←X 3Σ−g band system of jet-cooled V2
Authors: Spain Eileen M. , Behm Jane M. , Morse Michael D. 
Published: July 2002

The 846 nm band system of jet-cooled 51V2 has been recorded using resonant two-photon ionization spectroscopy, and is assigned as the A′ 3Σ−u←X 3Σ−g band system. Both the Ω′=1u←Ω″=1g and Ω′=0+u←Ω″=0+g subbands of the 0–0 band have been rotationally resolved and analyzed. Although the transition could, in principle, correspond to a π*g←πu or σ*u←σg excitation, it is assigned as a δ*u←δg excitation. Either of the other two possibilities makes it difficult to rationalize the small reduction in bond length which accompanies the excitation [re(X 3Σ−g)=1.77 Å, r0(A′ 3Σ−u)=1.756 Å]. In addition, the second order spin–orbit splitting of the ground X 3Σ−g state is reanalyzed to predict the existence of a 1Σ+g state, arising from the same sσ2gdσ2gdπ4udδ2g electronic configuration as the X 3Σ−g ground state, at an energy about 1821 cm−1 above the ground state.
This allows a state previously observed in an electronic resonance Raman effect 1860 cm−1 above the ground state to be positively identified as the sσ2gdσ2gdπ4udδ2g, 1Σ+g state, which is responsible for the anomalous spin–orbit splitting in the ground X 3Σ−g state. A similar analysis of the spin–orbit splitting of the A′ 3Σ−u state predicts the location of the sσ2gdσ2gdπ4u dδ1gdδ*1u, 1Σ+u state at 13 426 cm−1 above the V2 X 3Σ−g(0+g) ground state.
Spectroscopic interrogation of heterocluster isomerization. II. Spectroscopy of (9,10 dichloroanthracene)⋅(rare gas)n heteroclusters
Authors: Ben-Horin Narda , Bahatt Dar , Even Uzi , Jortner Joshua 
Published: July 2002

In this paper we report on the electronic spectroscopy of mass-resolved heteroclusters of 9,10-dichloroanthracene (DCA) with rare-gas atoms, i.e., DCA⋅Arn (n=1–54), DCA⋅Krn (n=1–20), and DCA⋅Xen (n=1–14), which were interrogated by resonant two-photon two-color ionization in conjunction with mass spectrometric detection. We measured the spectral shifts δν and the linewidths (FWHM) Δ of the S0→S1 transition, the ionization potential shifts δI from S0, and the change Δτr in the pure radiative lifetime of S1, relative to the corresponding values for the bare DCA molecule. We were able to provide a global assignment of the structure of isomers of DCA⋅An (A=Ar,Kr) heteroclusters, which rests on six independent sources of information, i.e., the application of experimental combination rules and on the comparison between the results of the molecular dynamics (MD) simulations and the experimental data for δν, δI, and Δτr. The size dependence and the isomer specificity of δν, δI, and Δτr are well accounted for by microscopic theories for these spectroscopic observables in conjunction with MD simulations. The size dependence of the experimental linewidths was analyzed in terms of finite temperature MD simulations, which incorporate the effects of homogeneous and inhomogeneous line broadening. Our analysis provides an adequate description of the qualitative difference between the gradual line narrowing of DCA⋅Arn (n=20–34) and the abrupt onset of line narrowing of DCA⋅Krn (n≥16) heteroclusters, which are attributed to the reduction of inhomogeneous line broadening originating from the combined effects of homogeneous line broadening and of the isomer specificity of the spectral shifts.
The temperature dependence of the homogeneous linewidths provides means for internal cluster thermometry. The isomerization phenomena inferred from MD simulations of nuclear dynamics could not be identified by the cluster size dependence of δν, δI, Δτr, and Δ, in accord with the conclusions drawn from the MD simulations of these spectroscopic observables. Finally, we explored the evolution of condensed matter properties with increasing the heterocluster size, advancing cluster size equations, which quantitatively accounts for the smooth ‘‘transition’’ of the spectral shift and of the homogeneous line broadening of DCA⋅Arn heteroclusters to those of DCA in bulk solid Ar.
Pulsed and continuous wave electron nuclear double resonance patterns of aquo protons coordinated in frozen solution to high spin MN2+
Authors: Tan Xiaoling , Bernardo Marcelino , Thomann Hans , Scholes Charles P. 
Published: July 2002

For the water protons that coordinate to Mn2+, the frozen solution ENDOR (electron nuclear double resonance) spectra are made complex by the anisotropic electron–proton hyperfine interaction and by multiple contributions of the electron spin 5/2 manifold. A spin 5/2 Mn2+ ion having magnetic quantum numbers Ms=±1/2, ±3/2, ±5/2 and small zero-field splittings has overlapping electron spin EPR transitions. Proton hyperfine couplings to each of these electron spin states have yielded overlapping ENDOR patterns whose interpretation is nontrivial, even in so simple a system as Mn2+ ion having hexaaquo coordination. We have experimentally obtained and theoretically explained these proton ENDOR patterns and in so doing have laid the foundation for interpreting and sorting out frozen solution ENDOR patterns in more complex (enzyme) environments. Pulsed and cw ENDOR experiments showed features of metal-coordinated water protons occurring not only within a few MHz of the free proton frequency (as will happen for an electron spin 1/2 system) but extending over a range of up to 35 MHz. The EPR line of the Mn2+ S=5/2 manifold was broadened by zero-field splitting for hundreds of Gauss away from g=2.00, and the relative intensity of different ENDOR features reflected couplings to differing Ms spin states at varying fields across this EPR line.
An expression was derived to show the dependence of proton ENDOR frequencies on the electron spin quantum number, Ms, upon the principal values of the intrinsic proton hyperfine tensor, upon the direction of the magnetic field, and upon the free proton frequency. This expression provided the starting point for powder simulations of the overall ENDOR pattern. These ENDOR powder pattern simulations were not elementary extensions of first-order theory as often applied to single-crystallike ENDOR spectra obtained at frozen solution EPR extrema. These simulations addressed the interpretation and the conditions for obtaining consistent hyperfine information from nuclei hyperfine coupled to Mn2+ where all Ms levels of the Mn2+ ion can furnish contributions to ENDOR and EPR. The aquo protons yielded an isotropic coupling As=0.8 MHz and a dipolar coupling Ad=3.4 MHz, where A∥=2Ad+As (=7.6 MHz) and A⊥=As−Ad (=−2.6 MHz). Such couplings are in agreement with those obtained by proton ENDOR of [Mn(H2O)6]2+ in single crystals [R. DeBeer, W. DeBoer, C. A. Van’t Hof, and D. Van Ormondt, Acta Cryst. B29, 1473 (1973)].
Large CO2 clusters studied by infrared spectroscopy and light scattering
Authors: Disselkamp Robert , Ewing George E. 
Published: July 2002

Large CO2 clusters were formed by introducing room temperature gaseous mixtures of CO2 in argon into a cryogenic cell at 77 K. Rapid cooling of each mixture resulted in a highly supersaturated CO2 concentration, giving rise to homogeneous nucleation and thus cluster formation [F. F Abraham, Homogeneous Nucleation Theory, Advances in Theoretical Chemistry, Supplement 1 (Academic, New York, 1974), and references therein]. Experimental results will be presented here for CO2 in argon dilutions of 1:104, 1:2×105, and 1:106. Light scattering and infrared absorption techniques have been combined to estimate an average cluster radius of 0.20 μm for the 1:104 dilution sample, and an upper limit in cluster radius of 0.10 μm for the 1:2×105 dilution sample. Therefore, the higher dilution CO2:Ar mixtures led to the formation of smaller cluster sizes. Infrared structure in the ν3-asymmetric stretching region of the clusters will be discussed.
The quantum mechanical exciton model and the classical Mie model are only partially successful in explaining these experimental observations. Weak absorption features have been assigned to the naturally abundant 13C16O2 and 12C16O18O isotopes. The infrared structure attributed to these minority isotopes is relatively invariant with cluster size formed, and can be explained by the exciton model. This analysis suggests that, whatever overall shape the clusters have assumed, the CO2 molecules within the clusters have separations and orientations like those in the bulk crystal. Infrared spectra were collected at regular intervals over a period of 4 h for each sample. A monotonic decrease in the integrated infrared absorbance of the clusters with time was observed, with a characteristic half-life of 65, 180, and 230 min for the 1:104, 1:2×105, and 1:106 dilution samples, respectively. The average cluster radii obtained from light scattering and infrared absorption measurements have been used to calculate a sedimentation half-life of 60 and 180 min for the 1:104 and 1:2×105 dilution samples, respectively, which agreed well with the observed disappearance times. A cluster radius of 0.09 μm for the 1:106 dilution experiment is consistent with its sedimentation half-life of 230 min.
Vibrational predissociation of 9,10-dichloroanthracene—Mixed and homo rare gas atom clusters
Authors: Penner Abraham , Amirav Aviv 
Published: July 2002

Clusters of the form DCA(R1R2), where DCA=dichloroanthracene and R1, R2=Ar, Kr, and Xe were synthesized in a supersonic molecular beam. The mixed clusters were efficiently formed by the coexpansion of DCA in a mixture of two different rare gases with the heavier rare gas being in the minority. The clusters’ vibrational predissociation dynamics was probed using a nanosecond excimer pumped dye laser spectroscopy and energy resolved emission diagnostics. DCA was chosen for this study because of its high emission quantum yield and relatively few spectral interferences at high vibrational energy. The emission quantum yield of DCA–rare gas atom complexes was found to be unity at the electronic origin. The emission quantum yield is greatly reduced upon the increase of the vibrational energy being 0.052 at the 1390 cm−1 vibrational level. It was more than three times higher in the DCA–rare gas atom clusters at the 1390 cm−1 vibration, in comparison with that of the bare molecule, due to vibrational predissociation. The vibrational predissociation products have been identified using energy resolved emission. At 1390 cm−1, excess vibrational energy two argon atoms or one xenon atom could dissociate. For DCA(Kr)n, it is not clear whether one or two krypton atoms had dissociated. In DCA(XeAr) or DCA(XeKr) excited to the 1390 cm−1 vibration, either one of the two rare gas atoms could dissociate, but not both of them.
The results indicate that predominantly the weakest bound rare gas atom dissociates, although its vibrational modes seems less effectively coupled to the excited skeleton modes. The dissociation rates were determined by the relative emission intensity before and after the dissociation, which could be spectrally identified. The time scales for vibrational predissociation of all the various DCA clusters were found to be about 1 ns, independent of the rare gas identity. The results are interpreted by assuming the excitation of a vibrationally mixed 1390 cm−1 state which undergoes a secondary intramolecular vibrational energy redistribution (IVR) within the DCA chromophore to a combination mode which contains a low lying promoting vibrational character. This secondary IVR is the ‘‘bottleneck’’ precursor process whose time scale is intramolecular, being independent of the rare gas atom attached to the DCA. After this secondary IVR, the vibrational energy flows on a much shorter time scale to and between the rare gas atom–DCA vibrational modes, and the weaker bound atom statistically dissociates.
Ab initio potential energy surfaces and trajectory studies of A-band photodissociation dynamics: ICN*→I+CN and I*+CN
Authors: Amatatsu Yoshiaki , Yabushita Satoshi , Morokuma Keiji 
Published: July 2002

The photodissociation reaction of ICN in the A continuum has been theoretically studied based on ab initio potential energy surfaces and classical trajectories. Ab initio contracted spin–orbit configuration interaction calculations have been carried out to obtain potential energy surfaces (PES’s) of 3Π1, 3Π0+ and 1Π1 excited states, where results are fit to five diabatic potential functions and their couplings as functions of all three internal degrees of freedom. The transition dipoles at the Franck–Condon region have also been calculated. All the PES’s involved in photodissociation are bent near the Franck–Condon region. Classical trajectory calculations performed on these potential surfaces have produced results that are in agreement with various experimental findings and provide a basis for their interpretation. The calculations indicate that the absorption is a mixture of parallel and perpendicular transition. A reasonable I/I* branching ratio can be obtained by considering the effect of initial bending vibrations in addition to the character of mixed transitions. The I/I* channel selectivity of the CN rotation can be compared to the shape of PES’s with respect to the bending angle. The rotational excitation of the CN fragment is determined by the shape of PES’s on which trajectories travel before and after the transition.
The higher rotational component in the I channel is attributed to the energy gradient of 1Π1 with respect to the bending angle at the transition region where the C–I distance is between 5.0 and 8.0 a.u. The lower component in the I channel emerges from 3Π1. The average rotational distribution obtained with the proper weight of Boltzmann populations and transition intensities is in agreement with the experiment. This interpretation can also be applied to the rotational quantum number dependence of anisotropy parameters. Trajectory calculations on the 3Π1 surface alone, give a single Boltzmann rotational distribution. Reflecting the shape of PES’s with respect to the CN distance, the product CN vibration on 3Π0+ and 1Π becomes suppressed while that on 3Π1 becomes slightly more excited. The anisotropic parameter was also analyzed. Some comments on the femtosecond transition spectroscopy are also made.