bluuebunny/crossref_metadata_2025_split huggingface dataset:
State-specific vibrational predissociation and interconversion tunneling quenching at 3ν1 and 3ν2 of (HF)2
Authors: Chang Huan-C. , Klemperer William 
Published: July 2002

We report the second overtone (Δv=3←0) spectra of the free-HF (ν1) and bound-HF (ν2) stretches of (HF)2 using laser induced fluorescence. Subbands of K=0←0 and K=1←0 are detected near 900 nm with linewidths spanning almost two orders of magnitude. The line broadening (Δνpd) due to vibrational predissociation is not only mode specific but also is state specific. A fit of the spectral lines to a Voigt profile reveals Δνpd=10 GHz for the parallel band of 3ν2, and 0.10 and 1.9 GHz for the parallel and the perpendicular bands of 3ν1, respectively. The linewidths of these subbands are J and tunneling state independent. The K-dependent vibrational predissociation is attributed to near-resonant centrifugal interaction of the K=1 state with the K=1 combination mode of the bound HF stretch (3ν2) and the antisymmetric bend (ν5). The exceedingly state-specific behavior is at variance with elementary density of states arguments. Spectroscopic constants of these two K subbands and two tunneling states (A+ and B+) of 3ν1 are determined from their rotationally resolved manifolds. For the parallel band, we obtain band origins ν0=11 273.501 cm−1 (A+), 112 73.499 cm−1 (B+), rotational constants B̄=0.221 177 cm−1 (A+), 0.221 179 cm−1 (B+), and centrifugal distortion constants D=2.02×10−6 cm−1 (A+), 2.05×10−6 cm−1 (B+).
For the perpendicular band, ν0=11 299.850 cm−1 (A+), 11 299.847 cm−1 (B+), and B̄=0.222 02 cm−1 (A+), 0.222 04 cm−1 (B+). The interconversion tunneling splitting is found to be 0.0024 cm−1, showing that the tunneling motion of the dimer could be quenched entirely. For the 3ν2 where only the R branch is resolved, the breadth of the lines prevents accurate determination of its spectroscopic constants. The band is estimated to center at 11 043.09 cm−1 with a rotational B̄ constant of 0.2240 cm−1. All the constants indicate that a stronger hydrogen bond is formed at higher valence vibrational states. The shifts of the free- and the bound-HF stretching frequencies from that of the monomer are −99.306 and −329.72 cm−1, respectively. Finally, we present an analysis for the rotational dependence of the tunneling in states of v1, which suggests that the transition state, under the assumption of C2h geometry, has the HF units oriented at 33° with respect to the F–F axis.
Change of bond length in free-energy simulations: Algorithmic improvements, but when is it necessary?
Authors: Wang Lu , Hermans Jan 
Published: July 2002

Various methods are compared for calculating the constraint free energy in simulations with change of bond lengths. Bond forces can be evaluated as restraint forces with the use of flexible bonds, and also, when bond lengths are held fixed, as constraint forces calculated either from SHAKE displacements, or else from Gauss’ principle of least constraint, and these forces can then be used to calculate the potential of mean force or free energy for the bond length changes. An alternative is to use so-called mean-potential forces. Analysis of the equations derived from Gauss’ principle shows that the constraint force (and also the restraint force) contain a ‘‘dynamic’’ term, that depends on the molecular motion and for simple molecules averages to 2 kT/r, where r is the bond length. Integration of this term, which is not present with use of the mean-potential force, or in a Monte Carlo simulation, gives a free energy that corresponds to the change in conformational entropy of two particles maintained at a certain distance, when this distance is changed. It is unnecessary to compute this free energy term by simulation, as was done in earlier work. The accuracy and precision of these methods, and of methods in which the bond lengths do not change, are tested in a series of model calculations of increasing complexity. First, the equivalence of these methods is tested in a model system with small molecules whose motion is maintained by Brownian dynamics, and which can be subjected to very simple external forces, in order to permit very long simulations.
Second, a comparison is made of techniques for calculating free energy change with and without change of bond lengths, applied to the transformation of ethane into ethanol in water. A third test system is the conversion of an alanine residue into a serine residue in an α-helix in water. It is found that results are much improved if the ‘‘vanishing’’ atoms (in this case hydroxyl O and H) are coupled to a heat bath via Brownian forces. Statistical errors are estimated from four successive slow-growth simulation cycles. Calculations with twofold change of C–O and O–H bond lengths and linear coupling of the nonbonded energy terms are more precise than calculations without change of bond lengths and nonlinear coupling. The free energy change for the system with flexible bonds contains a significant contribution (circa 3 kJ mol−1) from elongation of the bond lengths as a result of interaction of the polar OH group with water. The constraint forces calculated from the SHAKE displacements and from Gauss’ principle turn out to be almost identical. The three methods for calculating the constraint forces achieve similar precision in the ethane/ethanol system as well as in the α-helix system. We also discuss the application of free energy calculations with changing bond lengths to changes of a molecule’s chemistry in the middle of a chain.
Signatures of large amplitude motion in a weakly bound complex: High-resolution IR spectroscopy and quantum calculations for HeCO2
Authors: Weida Miles J. , Sperhac Jeanette M. , Nesbitt David J. , Hutson Jeremy M. 
Published: July 2002

The infrared spectrum of the HeCO2 van der Waals molecule is recorded in the region of the CO2 ν3 asymmetric stretch via direct absorption of a tunable Pb–salt diode laser. HeCO2 is formed in a slit jet supersonic expansion; the slit valve and the stagnation gas must be precooled to −35 °C before substantial formation of the complex is observed. Sixty-six rovibrational transitions are recorded by exciting the ν3 asymmetric stretch of the CO2 monomer within the complex. Forty-three of these transitions can be assigned using internally consistent combination differences as a b-type band of a T-shaped asymmetric rotor. There are several indications that large amplitude motion is significant in HeCO2, including the poor quality of the fit to an asymmetric rotor model and the large positive inertial defects of Δ=8.54 and 10.98 uÅ2 in the ground and excited states, respectively. However, a hindered rotor analysis based on these inertial defects demonstrates that the CO2 motion within the complex is far from the free rotor limit. No evidence of predissociation broadening is observed, indicating a lifetime for the complex of τ≳6 ns. Quantum close-coupling calculations which correctly treat both angular and radial degrees of freedom are carried out on the full 2D HeCO2 potential energy surface of Beneventi et al. [J. Chem. Phys. 89, 4671 (1988)]. Comparison of this analysis with the experimental results demonstrates that the theoretical potential is too isotropic in the region of the potential minimum.
Predicted spectra from this model potential, however, indicate that the remaining 17 much weaker HeCO2 transitions are due to a ‘‘hot band’’ excitation out of the first intermolecular bending level, lying 9±2 cm−1 above the ground state. In sharp contrast to the ground vibrational state of HeCO2, an asymmetric rotor model fails qualitatively to characterize the rotational structure for the lowest excited bend. The simple physical reason for this is confirmed by inspection of the quantum wave functions; in the ground state the He atom is localized near the C atom in a T-shaped geometry, whereas in any of the excited bending states the He atom is largely delocalized around the CO2 molecular framework.
Far-wing excitation study on the transit region of Hg 3P1→3P0 intramultiplet process in collisions with N2 and CO
Authors: Ohmori K. , Kurosawa T. , Chiba H. , Okunishi M. , Ueda K. , Sato Y. , Nikitin E. E. 
Published: July 2002

Laser-pump and probe approach has been applied to the far wings of Hg 3P1−1S0 resonance line broadened by collisions with N2 and CO to measure excitation spectra for the formation of Hg(6 3P0) and Hg(6 3P1). The excitation spectra are highly asymmetric with the red wing being much more extended than the blue wing. The absolute ratio of nascent yields of Hg 3P0 to 3P1 is determined as a function of the excitation wave number. From these measurements, it is found, commonly for Hg–N2 and Hg–CO systems, that (a) the nascent product ratio, Hg(3P0)/Hg(3P1), grows on the red-wing surface (the Ã state) with increasing shift, Δν, of the excitation wave number from the line center and finally surpasses unity; (b) the blue-wing surface (the B̃ state) gives mostly Hg(3P1) but has a small chance to give Hg(3P0). Time constant τ0 for the Ã→3P0 process of Hg–N2 is found to change from 17 to 35 ns as the absorption distance Rc between Hg and N2 changes from 3.6 to 4.7 Å. From these values of τ0, the transition probability P(Ã→3P0) for a single approach of Hg–N2 to the turning point region is estimated to be about 3.7×10−5. The transition probability P(B̃→3P0) is about 270 times larger than P(Ã→3P0).
CO is about 20 times more effective than N2 for the B̃→3P0 process. The Rc dependence of τ0 can be qualitatively explained by the vibrational frequencies of the bound Ã state and the Franck–Condon factor between the bound Ã state and the free (repulsive) ã state arising from Hg(3P0)+N2. These findings suggest that the direct Ã→ã transition is realized in these Hg–N2 and Hg–CO collisions. This gives a remarkable contrast to Hg-atom collisions, where the A→3P0 process is parity-forbidden due to the 0+ and 0− characters of the A and a states, respectively. The coupling mechanisms for the Ã→ã and B̃→ã transitions in Hg–N2 collisions are discussed in detail. The theoretical estimate of the Ã→ã transition probability is made to be compared with the experimental value.
Solvation and solvent effects on the short-time photodissociation dynamics of CH2I2 from resonance Raman spectroscopy
Authors: Kwok Wai Ming , Phillips David Lee 
Published: July 2002

Resonance Raman spectra of CH2I2 have been obtained at excitation wavelengths of 369, 355, and 342 nm in cyclohexane solution and in methanol solution at excitation wavelengths of 355 and 342 nm. Resonance Raman spectra were also measured for CH2I2 in the vapor phase with an excitation wavelength of 355 nm. The resonance Raman spectra of CH2I2 exhibit most of their intensity in fundamentals, overtones, and combination bands of modes nominally assigned as the I–C–I symmetric stretch, the I–C–I bend, and the I–C–I antisymmetric stretch vibrations. The absorption spectra and resonance Raman intensities of the gas phase and methanol solution phase diiodomethane spectra were simulated using a simple model and time-dependent wave packet calculations. Normal mode coefficients from normal coordinate calculations were used to convert the motion of the wave packet on the excited electronic state surface from dimensionless normal coordinates into internal coordinates of the molecule. The short-time photodissociation dynamics of diiodomethane in the vapor phase shows that the two C–I bonds are lengthening by the same amount, the I–C–I angle becomes smaller, the H–C–I angles become larger, and the H–C–H angle becomes smaller.
The two C–I bonds appear essentially equivalent in the Franck–Condon region of the gas phase photodissociation which implies that the molecule chooses which C–I bond is broken after the wave packet has left the Franck–Condon region of the potential energy surface. Comparison of the gas phase resonance Raman spectrum with solution phase spectra obtained in cyclohexane and methanol solvents reveals that the short-time photodissociation dynamics are noticeably changed by solvation with a large solvent-induced symmetry breaking observed. In the Franck–Condon region of the solution phase diiodomethane photodissociation in methanol solvent the two C–I bond become larger by differing amounts, the I–C–I angle becomes smaller, the H–C–H angle becomes smaller, and the H–C–I angles differ from the corresponding gas phase values. During the initial stages of the solution phase photodissociation (at least in methanol and cyclohexane solvents) the two C–I bonds are not the same and this suggests that the molecule chooses which C–I bond will be broken soon after photoexcitation.
Onset of two-dimensional cellular flow in finite curved channels of large aspect ratio
Authors: Finlay W. H. , Nandakumar K. 
Published: July 2002

The development of streamwise-oriented, symmetric, two-dimensional vortices in curved channels of large aspect ratios is studied near the threshold of the first centrifugal instability. The nonlinear equations of motion governing the two-dimensional, stationary flows are solved numerically over a range of parameter values. The dynamical parameter is the normalized streamwise pressure gradient defined as ε=[(∂p/∂x)−(∂p/∂x)c]/(∂p/∂x)c, where (∂p/∂x)c is the critical value for the infinite geometry. The development of interior cells and the selection of the wavelength as ε is gradually increased through zero is quite different from that observed in Taylor vortex flow. For pressure gradients of 0.5% and 1.0% (ε=0.005, 0.01) above critical, the interior cells begin to grow spontaneously and are strongest in the middle of the channel. Unlike the interior cells in Taylor vortex flow, they are only weakly coupled to the end cells. The end cells (or Ekman vortices) are also found to be anomalously long.
As ε is increased further to 0.04 and 0.07, the amplitude and wavelength of the interior cells are more uniform. There is, however, a complex interaction between the Ekman vortices and their neighboring interior cells, often resulting in the formation of additional cells in that region. Next, a simple Ginzburg–Landau (GL) model is tested for weakly nonlinear, two-dimensional vortices. The coefficient in the steady form of this equation is evaluated for a wide parameter range using high accuracy calculations of infinite aspect ratio neutral stability curves. (When suitably normalized, neutral stability curves are found to vary only a little with radius ratio.) For large aspect ratio curved channels, predictions from the model are compared with results from numerical simulation. The variation with ε of vortex amplitude near the center of the duct is correctly predicted by the Ginzburg–Landau equation. For given ε, however, agreement of the spanwise variation of vortex amplitude and spacing between the numerical simulation and the model is not obtained. The development of consistent amplitude equations and boundary conditions that link the interior flow to the boundary is expected to be a challenging task.
Coherent structures in rotating non-neutral plasma
Authors: Lund Steven M. , Ramos Jesus J. , Davidson Ronald C. 
Published: July 2002

Nonaxisymmetric (∂/∂θ≠0) rotating equilibria are investigated theoretically for strongly magnetized, low-density (ωpe2/ωce2≪1) pure electron plasmas confined in cylindrical geometry. These two-dimensional equilibria are also called rotating coherent structures, and are stationary (time independent) in a frame of reference rotating with angular velocity ωr=const about the cylinder axis (r=0). Radial confinement of the pure electron plasma is provided by a uniform axial magnetic field B0ez, and a grounded, perfectly conducting, cylindrical wall is located at radius r=rw. The analysis is based on a nonrelativistic, guiding-center model in the cold-fluid limit (the continuity and Poisson equations) that treats the electrons as a massless fluid (me→0) with E×B flow velocity Ve=−(c/B0)∇φ×ez. Within this model, general rotating equilibria with electron density ne≡nR(r,θ−ωrt) and electrostatic potential φ≡φR(r,θ−ωrt) have the property that the electron density is functionally related to the streamfunction ψR=−eφR+ωr(eB0/2c)r2 by nR=nR(ψR).
The streamfunction ψR satisfies the nonlinear equilibrium equation ∇2ψR=−4πe2nR(ψR)+2ωreB0/c with ψR=ωr(eB0/2c)rw2≡ψw=const on the cylindrical wall at r=rw. Following a general discussion of rotating equilibria, an integral equation formulation of the nonlinear equilibrium equation is developed to investigate equilibria with ‘‘waterbag’’ (step-function) density profiles. In this investigation, a numerical method is formulated that can be used to construct diverse classes of highly nonlinear waterbag equilibria. This method is employed to investigate two classes of nonaxisymmetric equilibria that are nonlinear extrapolations of well-known small-amplitude equilibria. These two classes of rotating equilibria bear strong similarities to coherent structures observed experimentally by Driscoll and Fine [Phys. Fluids B 2, 1359 (1990)].
Digital Cognitive Behavioral Therapy for Insomnia Using a Smartphone Application in China
Authors: Zhang Cheng , Liu Yuxuan , Guo Xiaoming , Liu Yanan , Shen Yane , Ma Jing 
Published: March 2023

ImportanceDigital cognitive behavioral therapy for insomnia (DCBT-I) requires adaptation to different sociocultural contexts. Moreover, studies comparing DCBT-I and sleep education in the same operating interface are lacking.ObjectiveTo investigate the efficacy of a smartphone-based Chinese culture–adapted DCBT-I application (app) for insomnia compared with sleep education using the same app.Design, Setting, and ParticipantsThis was a single-blinded, randomized clinical trial conducted from March 2021 to January 2022. Screening and randomization were conducted at Peking University First Hospital. Follow-up visits were performed online or in the same hospital. After assessing for eligibility, eligible participants were enrolled and allocated (1:1) to DCBT-I or sleep education groups. Data were analyzed from January to February 2022.InterventionsA Chinese smartphone-based app with the same interface was used in both DCBT-I and sleep education groups over 6 weeks, with 1-, 3-, and 6-month follow-ups.Main Outcomes and MeasuresThe primary outcome was Insomnia Severity Index (ISI) scores with the intention-to-treat principle. Secondary and exploratory outcomes included sleep diary measures; self-reported scales assessing dysfunctional beliefs about sleep, mental health, and quality of life; and smart bracelet measures.ResultsOf 82 participants (mean [SD] age, 49.67 [14.49] years; 61 [74.4%] females), with 41 randomized to sleep education and 41 randomized to DCBT-I; 77 participants completed the 6-week intervention (39 participants in the sleep education group and 38 participants in the DCBT-I group; full analysis data set) and 73 completed the 6-month follow-up (per protocol data set). Mean (SD) ISI scores in the DCBT-I group were significantly lower than those in the sleep education group after the 6-week intervention (12.7 [4.8] points vs 14.9 [5.0] points; Cohen d = 0.458; P = .048) and at the 3-month follow-up (12.1 [5.4] points vs 14.8 [5.5] points; Cohen d = 0.489; P = .04). There were significant improvements from before to after the intervention for both the sleep education and DCBT-I groups, with large effect sizes(sleep education: d = 1.13; DCBT-I: d = 1.71). Some of the sleep diary measures and self-reported scales showed more improvements in the DCBT-I group than sleep education group, such as total sleep time (mean [SD]: 3 months, 403.9 [57.6] minutes vs 363.2 [72.3] minutes; 6 months, 420.3 [58.0] minutes vs 389.7 [59.4] minutes) and sleep efficiency (mean [SD]: 3 months, 87.4% [8.3%] vs 76.7% [12.1%]; 6 months, 87.5% [8.2%] vs 78.1% [10.9%]).Conclusions and RelevanceIn this randomized clinical trial, the smartphone-based Chinese culture-adapted DCBT-I improved insomnia severity compared with sleep education. Future multicenter clinical trials with large sample sizes are needed to validate its effectiveness in the Chinese population.Trial RegistrationClinicalTrials.gov Identifier: NCT04779372
Out-of-Pocket Spending for Non–Birth-Related Hospitalizations of Privately Insured US Children, 2017 to 2019
Authors: Carlton Erin F. , Becker Nora V. , Moniz Michelle H. , Scott John W. , Prescott Hallie C. , Chua Kao-Ping 
Published: March 2023

ImportancePrivately insured US children account for 40% of non–birth-related pediatric hospitalizations. However, there are no national data on the magnitude or correlates of out-of-pocket spending for these hospitalizations.ObjectiveTo estimate out-of-pocket spending for non–birth-related hospitalizations among privately insured children and identify factors associated with this spending.Design, Setting, and ParticipantsThis study is a cross-sectional analysis of the IBM MarketScan Commercial Database, which reports claims from 25 to 27 million privately insured enrollees annually. In the primary analysis, all non–birth-related hospitalizations of children 18 years and younger from 2017 through 2019 were included. In a secondary analysis focused on insurance benefit design, hospitalizations that could be linked to the IBM MarketScan Benefit Plan Design Database and were covered by plans with a family deductible and inpatient coinsurance requirements were analyzed.Main Outcomes and MeasuresIn the primary analysis, factors associated with out-of-pocket spending per hospitalization (sum of deductibles, coinsurance, and copayments) were identified using a generalized linear model. In the secondary analysis, variation in out-of-pocket spending was assessed by level of deductible and inpatient coinsurance requirements.ResultsAmong 183 780 hospitalizations in the primary analysis, 93 186 (50.7%) were for female children, and the median (IQR) age of hospitalized children was 12 (4-16) years. A total of 145 108 hospitalizations (79.0%) were for children with a chronic condition and 44 282 (24.1%) were covered by a high-deductible health plan. Mean (SD) total spending per hospitalization was $28 425 ($74 715). Mean (SD) and median (IQR) out-of-pocket spending per hospitalization were $1313 ($1734) and $656 ($0-$2011), respectively. Out-of-pocket spending exceeded $3000 for 25 700 hospitalizations (14.0%). Factors associated with higher out-of-pocket spending included hospitalization in quarter 1 compared with quarter 4 (average marginal effect [AME], $637; 99% CI, $609-$665) and lack of chronic conditions compared with having a complex chronic condition (AME, $732; 99% CI, $696-$767). The secondary analysis included 72 165 hospitalizations. Among hospitalizations covered by the least generous plans (deductible of $3000 or more and coinsurance of 20% or more) and most generous plans (deductible less than $1000 and coinsurance of 1% to 19%), mean (SD) out-of-pocket spending was $1974 ($1999) and $826 ($798), respectively (AME, $1123; 99% CI, $1069-$1179).Conclusions and RelevanceIn this cross-sectional study, out-of-pocket spending for non–birth-related pediatric hospitalizations were substantial, especially when they occurred early in the year, involved children without chronic conditions, or were covered by plans with high cost-sharing requirements.