Quantum and quasiclassical study of the collinear reaction O(3P) + H2 → OH + H using a LEPS and fitted AB initio potential energy surface

Accurate quantum calculations of reaction probabilities P^T_ν′←ν have been carried out for the collinear reaction O(³P) + H₂ (ν = 0,1) → OH(ν′) + H using a LEPS and fitted ab initio potential energy surface. The energy dependence of the P^T_{ν′ ← ν} is similar for both surfaces. Collinear quasiclassical trajectory calculations have also been carried out, for comparison, on the LEPS surface for ν = 0, 1 and 2.     

SCF ab-initio ground state potential energy surfaces for HCN and HCN−

SCF computations for the ground state potential surfaces of HCN and HCN^? are performed. These calculations predict that the ground state geometry of the radical anion is R_e(CH) = 2.12 bohr, R_e(CN) = 2.33 bohr and the bond angle θ = 121.7°. The calculations also show that the CH bond in HCN^? is much weaker than in HCN and is similar to the CH bond in HCO. The computed electron affinity is ?1.95 eV. Since the minimum on the potential energy curve for the anion is above the neutral curve rapid auto-ionization should occur to HCN and an electron.     

Integral and state-to-state cross sections for the reaction D + H2(νf) → HD(νf) + H: A quantum mechanical study within the infinite order sudden approximation

In this paper are presented quantum mechanical t-initial and t-average cross sections and rate constants for the reactions D + H₂(ν₁ = 0, 1) → HD(ν_f = 0, 1) + H. The calculations were done employing the infinite order sudden approximation. It was found that the t-average total cross sections overlap very nicely with the available classical cross sections. As for rate constants a reasonably good fit was found with available experimental results.     

Kinematic viscosities of ternary mixtures containing ethane-1,2-diol, 2-methoxyethanol and water from −10°C to 80°C

Kinematic viscosities (ν) of the ternary ethane-1,2-diol (1)+2-methoxyethanol (2)+water (3) solvent system have been measured for 36 ternary mixtures covering the whole miscibility range expressed by the condition 0<X₁,X₂,X₃<1, at 19 temperatures in the range −10≤t (°C)≤80. The measured values have been used to test some empirical equations of the type ν=ν(t) and ν=ν(X_i), in order to provide for useful interpolation procedures to obtain calculated values in correspondence to the experimental data gaps. From the experimental data, the excess kinematic viscosities (ν^E) have been calculated. Sign and magnitude of these quantities have been discussed in terms of type and nature of specific intermolecular interactions. Furthermore, derived quantities such as thermodynamic parameters of the viscous flow (ΔG*, ΔH* and ΔS*), have been analysed on the basis of the Eyring's model. All the investigated excess mixing properties indicate the probable absence of stable three-component adducts in this ternary solvent system.     

Violation of microscopic reversibility and the use of reverse quais-classical trajectories for calculating reaction cross sections

In order to calculate the transition probabilities (or cross sections) for reactive collisions, such as A + BC(ν, j)→ AB(ν′, j) + C, using the quasi-classical trajectory method, one quantizes the internal energy of the reagents and in addition adopts some algorithm for calculating the internal quantum numbers of the products. A serious consequence of this procedure is that the quasi-classical results do not obey microscopic reversibility. It is shown that for the collinear F + H₂(ν = 0) → FH(ν = 2, 3)+ H reaction (and its D₂ counterpart), the quasi-classical trajectory probabilities for the reverse reaction not only differ substantially from the forward ones but in general are in much better agreement with accurate quantum calculations. A similar situation was found for the collinear H + H₂(0) → H₂(1) + H reaction. We suggest that in doing quasi-classical calculations, the reverse of the process of interest should also be considered. Comparison of forward and reverse quasi-classical collinear calculations with accurate collinear quantum results could give an indication of whether forward or reverse calculations should be used for the three-dimensional case.     

The characteristic IR spectra of heterothiometallic cluster compounds

This article summarizes and presents the obtainable characteristic IR spectra of the existing heterothiometallic cluster compounds containing the [MXS₃]²⁻ (X=O, S; M=V, Mo, W, Re) moiety. The MS stretching vibration modes are classified into four categories including ν(MS_t), ν(Mμ₂-S), ν(Mμ₃-S) and ν(Mμ₄-S) according to the different conjunction ways between the transition metal and sulfur atoms. The structures of the heterothiometallic cluster compounds could be inferred from their characteristic IR spectra, the core structure's symmetry of the heterothiometallic clusters and the M/M′ ratio.     

Radiative lifetime of CO+ (X2∑+, ν) ions

The radiative relaxation of CO⁺(X²∑⁺, ν) ions produced by ionization of CO and of OCS with 70 eV electrons has been investigated using the monitor ion technique in a triple FT ICR spectrometer. Since the monitor reaction is exothermic for ν ≥ 1, the experimental lifetimes, 170 ms for CO⁺ from CO and 210 ms for CO⁺ from OCS, should correspond to the overall decay rate of ν ≥ 2 with a small contribution of ν = 1.These values being much larger than the theoretical lifetime of ν = 1 (128.5 ms), computer-simulated overall lifetimes for ν ≥ 1 and ν ≥ 2 have been determined using theoretical lifetimes calculated by Rosmus and Werner and a vibrational population deduced from photoelectron spectroscopy of CO with 40.8 eV photons (Gardner and Samson). The computer-simulated lifetimes, 250 ms for ν ≥ 1 and 125 ms for ν ≥ 2, are indeed about twice as large as the theoretical lifetimes for ν = 1 and ν = 2, respectively, indicating that the large experimental lifetimes may be accounted for by radiative cascade from the upper vibrational levels.     

Energy distribution among reaction products. XIV. F + CH4, F + CH3X(X  Cl,Br, I), F + CHnCl4−n(n = 1−3)

The infrared chemiluminescence technique has been used to obtain relative rate constants k(ν′) for HF(ν′) formed in the following reaction:

For reaction (1) the detailed rate constants [k(ν′ = 1) = 0.30;k(ν′ = 2) = 1.00; k(ν′ = 3) = 0.15; mean fraction of the available energy entering vibration <?^′_ν> = 0.56] confirmed, at much lower reagent pressures, results obtained by previous workers. In series I there was a slight increase in fraction of the energy entering vibration as the molecular reagent altered from CH₃Cl to CH₃Br to CH₃I, viz <?^′_ν> = 0.50 (1a), <?^′_ν> = 0.58 (1b), <?^′_ν> = 0.60 (1c). In series 2, by contrast, there was a marked decrease in fractional conversion of the available energy into vibration with increasing chlorination of the molecular reagent; <?^′_ν> = 0.50 (1a), <?^′_ν> = 0.23 (2a), <?^′_ν> = 0.13 (2b). The rate constants into ν′ = 0, k(ν′ = 0), were obtained by extrapolation of surprisal plots; the trends for both series were, however, also evident from k(ν′ > 0). No separate initial rotational distribution was observed for any of these reactions, indicating that the peak of the initial distribution is not far removed from a 300 K thermal distribution. The decrease in <?^′_ν> for the HF products along series 2 was tentatively ascribed to increasing internal excitation in the ejected radicals CH₂Cl, CHCl₂, CCl₃, due to increase in the number of secondary encounters between HF and the departing radical.     

Study of energy transfer from laser excited CO2 to chloromethanes

Collisional energy transfer from CO₂(ν₃) to chloromethanes was studied in the temperature range 300–700 K using the laser induced fluoresce technique. Theoretical calculations using SSH and SB theories were carried out to identify the CO₂(ν₃) deactivation process. The experimental probabilities were found to decrease linearly with increasing number of substituted chlorine atoms.     

Experimental and quantum chemical study of pyrrole self-association through N-H?π hydrogen bonding

An FT-IR study of pyrrole self-association in CCl₄ solutions was carried out. According to the IR measurements, pyrrole forms self-associated dimeric species via N-H?π hydrogen bonding. This was also confirmed by quantum chemical calculations for pyrrole monomer and dimer at B3LYP/6-31++G(d,p) level of theory. A T-shaped minimum was located on B3LYP/6-31++G(d,p) PES of pyrrole dimer characterized with a hydrogen bond of an N-H?π type, with centers-of-mass separation of monomeric units of 4.520 Å, H?π distance of 2.475 Å, the interplanar angle between the two monomeric units being 72.9°. The anharmonic vibrational frequency shift upon dimer formation calculated on the basis of 1D DFT vibrational potentials is in excellent agreement with the experimental data (84 vs. 87 cm⁻¹). Harmonic vibrational analysis predicts somewhat smaller shift (68 cm⁻¹). On the basis of NIR spectroscopic data, anharmonicity constants for the 2ν(N-H) and 2ν(N-H?π) vibrational transitions were calculated. The orientational dynamics of monomeric and self-associated pyrrole species was studied within the framework of the transition dipole moment time correlation function formalism. The period of essentially free rotation in the condensed phase reduces from 0.05 ps for the monomeric pyrrole to 0.02 ps for the proton-donor molecule within the dimer.     

Synthesis of (NHC)Rh(cod)Cl and (NHC)RhCl(CO)2 complexes – Translation of the Rh- into the Ir-scale for the electronic properties of NHC ligands

Twenty-three different Rh complexes of the (NHC)RhCl(cod) and (NHC)RhCl(CO)₂ type were synthesized from [RhCl(cod)]₂. The electron donating nature of the NHC ligands was changed in a systematic manner. The redox potentials of the various (NHC)RhCl(cod) and the ν(CO) of the various (NHC)RhCl(CO)₂ were determined. A correlation of the Rh redox potentials and the Rh ν(CO), respectively, with the related data from analogous (NHC)IrCl(cod) and (NHC)IrCl(CO)₂ complexes established two linear relationships. The linear regression (R² = 0.993) of the Rh and the Ir redox potentials results in an equation for the redox potential transformation: E_1/2(Ir) = 1.016 · E_1/2(Rh) ? 0.076 V. The linear regression (R² = 0.97) of the Rh and Ir ν_av(CO) results in an equation for the ν_av(CO) transformation: ν_av(CO)Ir = 0.8695 · ν_av(CO)Rh + 250.7 cm^?1. In this manner the Rh and the Ir-scale for the determination of the electron donating properties of NHC ligands are unified.     

Potential energy curve of 1Σ+ Li+/He

The potential energy curve of the system Li⁺/He has been determined with moderately large basis sets for 0.5 ? r ? 10.0 a₀ both at the SCF level and including correlation. The present SCF results predict a deeper well (?0.00248 au) at a smaller r(3.66 a₀) compared with earlier calculations. Correlation deepens the well further (?0.00274 au), but pulls it inward slightly (3.63 a₀). In the repulsive part the calculated curve lies above the experimental one, especially at shorter distances. A similar behavior has been noted in the systems Li⁺/H₂, Li⁺/CO and Li⁺/N₂, suggesting that the experimental determinations may underestimate the interaction in this region by 10–20%.     

Kinetic models for the CH4(ν3) deactivation in CH4-CH4 collisions. Interpretation of experimental results

Various kinetic models for the CH₄(ν₃) deactivation in CH₄-CH₄ collisions at low temperatures (T ? 300 K) are proposed and applied to interpret recently published experimental results. We discuss the value of the rate constant of the single-quantum process CH₄(2ν₄) → CH₄(ν₄) (V-T,R process).     

The lack of leaving-atom isotope effects on rotational state distributions in M* + H2 (HD) → MH(ν, N)+H (D) reactions: “Half-collision” classical trajectories on model H-M-H anisotropic potential surfaces

Simple “half-collision” classical trajectories on model potential surfaces show that the lack of leaving-atom isotope effects on initial rotational state distributions P(N) in reactions of the type M + H₂ (HD) → MH (ν, N)+H (D) would result from decomposition of H-M-H (D) intermediates on anisotropic potential surfaces.     

Optical properties of alkaline-earth metal oxides from first principles

This study reports the results of an ab initio electronic and optical calculation of alkaline-earth metal oxides (MgO, CaO, SrO and BaO) in the NaCl crystal structure using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory. The exchange-correlation potential is treated by the generalized gradient approximation within the Perdew et al scheme. Moreover, the Engel–Vosko GGA formalism is applied so as to optimize the corresponding potential for band structure calculations. The real and imaginary parts of the dielectric function ?(ω), the optical absorption coefficient I(ω), the reflectivity R(ω) and the energy loss function are calculated by random phase approximation (RPA). The calculated results show a qualitative agreement with the available experimental results in the sense that we can recognize some peaks qualitatively, those due to single particle transitions. Furthermore the interband transitions responsible for the structures in the spectra are specified. It is shown that the oxygen 2p states and metal d states play the major role in optical transitions as initial and final states respectively. The effect of the spin–orbit coupling on the optical properties is also investigated and found to be quite small, especially in the low energy region. The dielectric constants are calculated and compared with the available theoretical and experimental results.     

Correlation analysis of characteristic infrared spectral data of hydantoin derivatives: evidence for vibrational coupling

The characteristic vibrations (ν_CO and ν_CC) of a large number of hydantoin derivatives are reported. Especially the very fine correlations ν_CO(sym) versus ν_CO(asym) (r²=0.985) but also successful correlations of the vibration wave numbers to HAMMETT's substituent constants and some other experimental parameters (pK_s, OxPot, RedPot) as well, corroborate reassignments of previously obtained results [Monatsh. Chem. 92 (1961) 361] and prove the doublet obtained in the region of the CO stretching vibrations to be the symmetrical and anti-symmetrical vibrational modes of a mechanically coupled system of two quasi-symmetrical CO bonds.     

Reducedab initio theoretical internuclear potentials of diatomic molecules

Ab initio theoretical ground state potentials of diatomic molecules calculated with the use of the variational CI-MO (configuration interaction method based on molecular orbitals) are analyzed with the use of the RPC (reduced potential curve) method. It is shown on a series of examples that the following statement is true even for inaccurateab initio calculations: in reduced form, the theoretical potential coincides to a high degree of accuracy with the reduced RKR (Rydberg-Klein-Rees) potential calculated from the spectroscopic data. Thus, with the use of the RPC method, even inaccurateab initio calculations (in particular for heavier molecules) may be used for the construction of rather accurate internuclear potentials and hence obtain a practical significance. The statement also holds for excited states if strong perturbations are not present.     

Quantum-mechanical differential reaction cross sections for the F + H2(ν = 0) - FH(ν′= 2.3) + H reaction

Velocity scatterring angle intensity maps for the F + H₂(ν = 0): j = 0) $\text{\$}\text{?}$FH(ν′ = 2, 3: j′) + 11 reaction are predicted from quantum-mechanical J conserving, calculations. The extent of the shift in the angular distribution from backscattering at 1.8 kcal/mole to sideways scattering (intensity peak at 100°) at 3.0 kcal/mole is in quantitative agreement with recent crossed molecular beans experiments.     

Density and temperature effects on relative Raman intensities in liquid toluene

Raman spectra of toluene at pressures up to 4.1 kbar and temperatures up to 100°C, have been studied. The frequency and intensity changes of the symmetric (ν_6a) and antisymmetric (ν_6b) ring breathing vibrations have been related principally to changes in density. Increasing density at constant temperature increases I(ν_6b/ν6a) and increases the frequency of (ν_6a) but has little effect on the frequency of ν_6b. Increasing temperature at constant density decreases I(ν_6b/ν_6a) and increases the frequency of ν_6a but has little effect on the frequency of ν_6b. An explanation of the different intensity changes with density for these two bands is suggested in terms of the contrasting volume changes associated with the two modes.