Isotopic Effects on Stereodynamics for Ca＋HCI, Ca＋DCI, and Ca＋TCl Reactions

The vector correlations in Ca＋HCl, Ca＋DCl, and Ca＋TCl reactions have been investigated by means of the quasi-classical trajectory calculations on PES constructed by means of multireference configuration interaction. The distributions of P（θr）, P（Фr） and the PDDCSs of （2π/σ）（dσ00/dωt）, （2π/σ）（dσ20/dωt）, （2π/σ）（dσ22＋/dωt）, （2π/σ）（dσ21-/dωt） have been calculated based on the surface. The remarkable isotopic effects in the reactions are observed, and the mechanism which may be ascribed to different mass factors is discussed.

Evaluation of the carbon isotopic effects of NDIR and CRDS analyzers on atmospheric CO2 measurements

Non-dispersive infrared （NDIR） and cavity ring-down spectroscopy （CRDS） CO2 analyzers use 12CO2 isotopologue absorption lines and are insensitive to all or part of other CO2-related isotopologues. This may produce biases in CO2 mole fraction measurements of a sample if its carbon isotopic composition deviates from that of the standard gases being used. To evaluate and compare the effects of carbon isotopic composition on NDIR and CRDS CO2 analyzers, we prepared three test sample air cylinders with varying carbon isotopic abundances and calibrated them against five standard cylinders with ambient carbon isotopic composition using CRDS and NDIR systems. We found that the CO2 mole fractions of the sample cylinders measured by G1301 （CRDS） were in good agreement with those measured by LoFlo （NDIR）. The CO2 values measured by both instruments were higher than that of a CO2 isotope measured by G2201i （CRDS） analyzer for a test cylinder with depleted carbon isotopic composition δ^13C =-36.828%0, whereas no obvious difference was found for other two test cylinders with 3 δ^13C=-8.630‰ and δ^13C=-15.380‰, respectively. According to the theoretical and experimental results, we concluded that the total CO2 mole fractions of samples with depleted isotopic compositions can be corrected on the basis of their 12CO2 values calibrated by standard gases using LoFlo and G1301 if the fi13C and fi180 values are known. Keywords NDIR and CRDS analyzers, Carbon isotopic effects, CO2 measurements

Heterolytic and homolytic C-D bond dissociation energies of NADH models in acetonitrile and primary isotopic effects on hydride versus hydrogen atom transfer reactions

Heterolytic and homolytic C D bond dissociation energies of three NADH models: BNAH-4,4-d 2 , HEH-4,4-d 2 and AcrD 2 in acetonitrile were first estimated by using an efficient method. The results showed that the heterolytic C D bond dissociation energies are 65.2, 70.2, and 81.9 kcal/mol and the homolytic C D bond dissociation energies are 72.66, 70.69, and 74.95 kcal/mol for BNAH-4,4-d 2 , HEH-4,4-d 2 , and AcrD 2 , respectively. According to the bond dissociation energy differences of isotope isomers, an interesting conclusion can be made that the primary kinetic isotope effects are dependent not only on the zero-point energy difference of the isotope isomers, but also on the types of C D bond dissociations, and the C D bond homolytic dissociations should have much larger primary kinetic isotope effects (26.9 28.8) than the corresponding C D bond heterolytic dissociations (3.9-5.4).

The isotopic effects in the IR-multiphoton excitation of molecules with c_(2v) symmetry

Quantum dynamical calculations for the IR-multiphoton excitation of H_2O,D_2O and T_2O are presented using a generalized Hamiltonian for XY_2 molecules.The energy spectra obtained from this Hamiltonian are in good agreement with those of the experiments.The long time average of the transition probabilities and the isotopic effects are discussed in detail,

Simulation of Isotopic Angular Effects under Ion Bombardment of a^(92)Mo-^(100)Mo Target

Under 5 keV Ar ion bombardment of a 92Mo-100Mo target, we have investigated isotopic angular effects by means of the static and the dynamic Monte Carlo programs. Our calculated results are in quantitative agreement with the measured and other calculated results. The conclusion consistences among theories. simulations and measurements are also discussed.

Isotopic Effects on Stereodynamics of the C^+ + H_2→CH^+ + H Reaction

The effects of isotope substitution on stereodynamic properties for the reactions C^+ + H_2/HD/HT →CH^+ + H/D/T have been studied applying a quasi classical trajectory method occurring on the new ground state CH_2^+ potential energy surface [J. Chem. Phys. 142(2015) 124302]. In the center of mass coordinates applying the quasi classical trajectory method to investigate the orientation and the alignment of the product molecule. Differential cross section and three angle distribution functions P(θ_r), P(ф_r), P(θ_r, ф_r) on the potential energy surface that fixed the collision energy with a value is 40 kcal/mol have been studied. The isotope effect becomes more and more important with the reagent molecules H_2 changing into HD and HT. P(θ_r, ф_r) as the joint probability density function of both polar angles θ_r and ф_r, which can illustrate more detailed dynamics information. The isotope effect is obvious influence on the properties of stereodynamics in the reactions of C^+ + H_2/HD/HT → CH^+ + H/D/T.

Theoretical study of kinetic isotope effects for vacancy diffusion of impurity in solids

Theoretical studies of the diffusionalisotope effect in solids are still stuck in the 1960s and 1970s.With the development of high spatial resolution mass spectrometers,isotopic data of mineral grains are rapidly accumulated.To dig up information from these data,molecularlevel theoretical models are urgently needed.Based on the microscopic definition of the diffusion coe fficient(D),a new theoretical framework for calculating the diffusional isotope effect(DIE(v))(intermsofD*/D)forvacancy-mediated impurity diffusion in solids is provided based on statistical mechanics formalism.The newly derived equation shows that theDIE(v)can be easily calculated as long as the vibration frequencies of isotope-substituted solids are obtained.The calculatedDIE(v)values of^(199)Au/^(195)Au and^(60)Co/^(57)Co during diffusion in Cu and Au metals are all within 1%of errors compared to the experimental data,which shows that this theoretical model is reasonable and precise.

Isotope Effects on Two-Photon Population Transfer Processes of HF and DF

The isotope effects of XF （X=H, D） on the population transfer process via two-photon resonance excitation are investigated by solving the time-dependent SchrSdinger equation. The vibrational levels v=0 and 2 of the ground electronic state are taken to be the initial and target states, respectively, for the two molecular systems. The influences of the field peak amplitude and pulse duration on the population transfer process are discussed in detail. The pulse duration is required to be longer than 860 fs for the DF molecule to achieve a relatively high transfer probability （more than 80%）, while the one for the HF molecule is just required to be longer than 460 fs. Moreover, the intermediate level v=1 and the higher level v=3 may play more important roles in the two-photon resonance process for the DF molecule, compared to the roles in the process for the HF molecule.

Quantum Dynamics Calculations on Isotope Effects of Hydrogen Transfer Isomerization in Formic Acid Dimer

We present a quantum dynamics study on the isotope effects of hydro-gen transfer isomerization in the formic acid dimer,and this is achieved by multidimensional dy-namics calculations with an efficient quantum mechanical theoretical scheme developed by our group,on a full-dimensional neural network ab initio potential energy surface.The ground-state and fundamental tun-neling splittings for four deuterium isotopologues of formic acid dimer are considered,and the calculated results are in very good general agreement with the avail-able experimental measurements.Strong isotope effects are revealed,the mode-specific funda-mental excitation effects on the tunneling rate are evidently influenced by the deuterium sub-stitution of H atom with the substitution on the OH bond being more effective than on the CH bond.Our studies are helpful for acquiring a better understanding of isotope effects in the double-hydrogen transfer processes.

Influence of Isotope on Shell Effects of Pre-scission Particle Evaporation

The shell effects on the particle evaporation prior to fission for three Pb isotopes, ^204Pb, ^208Pb, and ^212pb,as well as three Sn isotopes, ^128Sn, ^132Sn, and ^136Sn, are explored by a diffusion model. Calculations show that the magnitude of shell effects in the emission of particles changes with the neutron-to-proton ratio N/Z of these fissioning nuclei, and this change is affected significantly by the spin and excitation energy of the system. It is shown that high angular momentum enhances the dependence of shell effects on the N/Z while high excitation energy weakens such a dependence.

Influence of Isotope Effects on Product Polarizations of N(~2D)+D_2, N(~2D)+H_2 and N(~2D)+HD Reactive Systems

To figure out the influence of isotope effect on product polarizations of the N（2D）＋D2 reactive system and its isotope variants, quasi-classical trajectory（QCT） calculation was performed on Ho＇s potential energy surface（PES） of 2A″ state. Product polarizations such as product distributions of P（θr）, P（φr） and P（θr,φr）, as well as the generalized polarization-dependent differential cross sections（PDDCSs） were discussed and compared in detail among the four product channels of the title reactions. Both the intermolecular and intramolecular isotope effects were proved to be influential on product polarizations.

Dynamics of the reaction of O with H_2 and its isotopic variants in different rotational excited states

Scalar properties and vector correlations of the reactions of O＋H2 →OH＋H, O＋HD→OH＋D, O＋DH→OD＋H, and O＋D2 -＋OD＋D at collision energies of 25 and 34.6 kcal/mole have been studied via the quasi-classical-trajectory （QCT） method based on a BMS1 potential energy surface （PES）. The generalized polarization-dependent differential cross section and the distributions of the dihedral angle at the collision energy of 34.6 kacl/mole are presented. The calculated results indicate that both the reagent rotational angular momentum and the mass factor have a significant influence on the scalar properties and vector correlations of the title reactions.

Investigation of isotope effects of dynamic properties for H(D) + OF reactions by the quasi-classical trajectory method

Quasi-classical trajectory （QCT） calculations are employed to study the dynamic properties for H（D）＋OF reactions on the adiabatic potential energy surface （PES） of the 1^3A″ triplet state. Obvious differences between the reaction probabilities for J=0, integral cross sections for J≠0, branch ratios of the product and internuclear distances as well as product rotational alignments between the title reactions axe found. These differences are attributed mainly to the different reduced masses of the reactants and the different zero-point energies （ZPEs） of the transition state.

Quasi-classical Trajectory Study of F-I-H20→HF-I-OH Reaction： Influence of Barrier Height, Reactant Rotational Excitation, and Isotopic Substitution

The reaction dynamics of the F＋H20/D20→HF/DF＋OH/OD are investigated on an accurate potential energy surface （PES） using a quasi-classical trajectory method. For both isotopomers, the hydrogen/deuterium abstraction reaction is dominated by a direct rebound mechanism over a very low ＂reactant-like＂ barrier, which leads to a vibrationally hot HF/DF product with an internally cold OH/OD companion. It is shown that the lowered reaction barrier on this PES, as suggested by high-level ab initio calculations, leads to a much better agreement with the experimental reaction cross section, but has little impact on the product state distributions and mode selectivity. Our results further indicate that rotational excitation of the H20 reactant leads to significant enhancement of the reactivity, suggesting a strong coupling with the reaction coordinate.

Deuterium Isotope Effects in Oxidative Deamination of L-Alanine Catalyzed by L-Alanine Dehydrogenase

Solvent and kinetic isotope effects in the reaction of oxidative deamination of L-alanine, catalyzed by L-alanine dehydrogenase, AIaDH, （EC 1.4.1.1） were determined using a non-competitive spectroscopic method. The progress of the reaction was monitored spectrophotometrically by measuring the increasing absorbance of the reduced form of NADH at 340 nm. L-alanine, stereospecifically labeled with deuterium was synthesized by enzymatic reductive amination of pyruvate in presence of [（4R）-2H]-NADH, which was obtained by deuterium transfer from deuteriated formic acid to NAD~ catalyzed by FDH （formate dehydrogenase） （EC 1.2.1.2）. [2-2H]-L-alanine, the product of enzymatic synthesis catalyzed by AIaDH, was obtained with 75% deuterium enrichment and values of isotopic effects were approximated to the values corresponding to 100% of deuterium incorporation. The enzyme AIaDH isolated from Bacillus subtilis shows pro-R stereospecificity, what indicates that hydrogen is exclusively transferred from pro-R position at C-4 of the nicotinamide ring of NADH to C-2 of pyruvate to form L-alanine. Some intrinsic mechanistic details of enzymatic oxidative deamination of L-alanine were discussed using determined numerical values of kinetic and solvent isotope effects on Vmax and Vmax,│KM

Oxygen Isotope Effects on T_(c) Related to Polaronic Superconductivity in Underdoped Cuprates

The planar oxygen isotope effect on Tc observed in copper oxide superconductors is remarkable in that it increases from near nil at optimal doping to a value twice that derived from BCS theory in the underdoped region. This behavior is quantitatively followed by a formula proposed by Kresin and Wolf in 1994 for polarons along the c-axis. Herein it is revisited in a more transparent way, and it is pointed out that the heterogeneity of pairing is relevant and has to be taken into account to explain the unusual planar isotope effects on Tc in underdoped cuprates.

Study of the Isotope Effects of Novel Superconducting LaH₁₀-LaD₁₀and H₃S-D₃S Systems

This paper is directed to study the isotope effects of some superconducting materials that have a strong coupling coefficient λ > 1.5, and focuses on new superconducting materials whose critical temperature is close to room temperature, specifically LaH10-LaD10 and H3S-D3S systems. The Eliashberg-McMillan (EM) model and the recent Gor’kov-Kresin (GK) model for evaluating the isotope effects coefficient α were examined for these systems. The predicted values of α as a function of pressure, as compared to experimental values led to inference that these two models, despite their importance and simplicity, cannot be considered complete. These models can be used to calculate isotope effect of most superconducting materials with strong coupling coefficients but with critical reliability. The significance of studying the isotope effect lies in the possibility of identifying the interatomic forces that control the properties of superconducting materials such as electrons-mediated phonons and Coulomb interactions.

Vibronic effect study of ^(1)A_(2) state of H_(2)O and D_(2)O

The generalized oscillator strengths of the dipole-forbidden excitations of the ^(1)A_(2) of H_(2)O and D_(2)O were calculated with the time dependent density functional theory,by taking into account the vibronic effect.It is found that the vibronic effect converts the dipole-forbidden excitation of the ^(1)A_(2) into a dipole-allowed one,which enhances the intensities of the corresponding generalized oscillator strength in the small squared momentum transfer region.The present investigation shows that the vibronic effect of H_(2)O is slightly stronger than that of D_(2)O,which exhibits a clear isotopic effect.

Interaction of Impurity (Li, Be, B and C) and Hydrogen Isotope Pellet Injection with Reactor-relevant Plasmas

Based on the two-dimensional kinetic ablation theory of the hydrogen pellet ablation developed by Kuteev [B.V. Kuteev, Nuclear Fusion, 35 (1995) 431], an algorithm of erosion speed and ablation rate calculations for Li, Be, and B impurity pellets in reactor-relevant plasma has been derived. Results show compatibilities of lithium pellet injection used in α-particle diagnostics are positive in comparison with other solid impurity pellets (e.g. Be, B and C). Using the 2-D Kuteev lentil model, including kinetic effects, we find that currently existing pellet injection techniques will not meet core-fueling requirements for ITER-FEAT. A pressure as high as 254 MPa must be applied to a pellet accelerator with a 200 cm-long single-stage pneumatic gun, in order to accelerate a pellet with a radius rpo = 0.5 cm to a velocity of vpo, 24 × 105 cm/s penetrating 100 cm into the ITER plasma core. Comparisons of pellet velocity- and radius-dependent penetration depth between the Neutral Gas Shielding and the Kuteev's models are made. However, we find that the isotopic effects can lead to a 33% lower pellet speed for solid DT, compared to an identical H2 pellet penetrating the same length in ITER-FEAT plasma, and our calculations show that HFS injection will much improve core fueling efficiency.

Theoretical Study on Stereodynamics of Reactions of N（^2D）＋H2→NH＋H and N（^2D）＋D2→ND＋D

The vector correlations between products and reagents for the title reactions have been calculated by the quasi-classical trajectory method at a collision energy of 21.32 kJ/mol on an accurate potential energy surface of Ho et al. （J. Chem. Phys. 119, 3063 （2003））. The peaks of the product angular distribution are found to be in both backward and forward directions for the two title reactions. The product rotational angular momentum is not only aligned, but also oriented along the negative direction of y-axis. These theoretical results are in good agreement with recent experimental findings for the two title reactions. The isotopic effect is also revealed and primarily attributed to the difference of the mass factor in the two title reactions.