Doublet rotational energy transfer of the SH (X ²Π, v'=0) state by collisions with Ar

The rotational energy transfer (RET) by Ar collisions within the SH X?(2)Π (v' = 0, J' = 0.5-10.5) state is characterized. The integral cross sections as a function of collision energy for each rotational transition are calculated using a quantum scattering method in which the constructed potential energy functions are based on a ground state potential energy surface (PES) reported previously. On the other hand, a laser-induced excitation fluorescence technique is employed to monitor the relaxation of the rotational population as a function of photolysis-probe delay time following the photodissociation of H(2)S at 248 nm. The rotational population evolution is comparable to its theoretical counterpart based on calculated Λ-resolved RET rate constants. The propensity in Λ-resolved RET transitions is found to approximately resemble the case of OH(X?(2)Π, v' = 0) + Ar. The Λ-averaged RET collisions are also analyzed and result in several propensity rules in the transitions. Most propensity rules are similar to those observed in the collisions of SH(A?(2)Σ(+)) by Ar. However, the behavior of the conserving ratio, defined as rate constants for spin-orbit conserving transition divided by those for spin-orbit changing transition, shows distinct difference from those described by Hund's case (b).     

Fully Λ-doublet resolved state-to-state differential cross-sections for the inelastic scattering of NO(X) with Ar

Fully Λ-doublet resolved state-to-state differential cross-sections (DCSs) for the collisions of the open-shell NO(X, (2)Π(1/2), ν = 0, j = 0.5) molecule with Ar at a collision energy of 530 cm(-1) are presented. Initial state selection of NO(X, (2)Π(1/2), j = 0.5, f) was performed using a hexapole so that the (low field seeking) parity of ε = -1, corresponding to the f component of the Λ-doublet, could be selected uniquely. Although the Λ-doublet levels lie very close in energy to one another and differ only in their relative parities, they exhibit strikingly different DCSs. Both spin-orbit conserving and spin-orbit changing collisions have been studied, and the previously unobserved structures in the fully quantum state-to-state resolved DCSs are shown to depend sensitively on the change in parity of the wavefunction of the NO molecule on collision. In all cases, the experimental data are shown to be in excellent agreement with rigorous quantum mechanical scattering calculations.     

Rotationally elastic and inelastic dynamics of NO(X2Π, v = 0) in collisions with Ar

A combined theoretical and experimental study of the depolarization of selected NO(X(2)Π, v = 0, j, F, ?) levels in collisions with a thermal bath of Ar has been carried out. Rate constants for elastic depolarization of rank K = 1 (orientation) and K = 2 (alignment) were extracted from collision-energy-dependent quantum scattering calculations, along with those for inelastic population transfer to discrete product levels. The rate constants for total loss of polarization of selected initial levels, which are the sum of elastic depolarization and population transfer contributions, were measured using a two-color polarization spectroscopy technique. Theory and experiment agree qualitatively that the rate constants for total loss of polarization decline modestly with j, but the absolute values differ by significantly more than the statistical uncertainties in the measurements. The reasons for this discrepancy are as yet unclear. The lack of a significant K dependence in the experimental data is, however, consistent with the theoretical prediction that elastic depolarization makes only a modest contribution to the total loss of polarization. This supports a previous conclusion that elastic depolarization for NO(X(2)Π) + Ar is significantly less efficient than for the electronically closely related system OH(X(2)Π) + Ar [P. J. Dagdigian and M. H. Alexander, J. Chem. Phys. 130, 204304 (2009)].     

Rotational energy transfer in the NO A 2Σ+(v' = 0) state with He and Ar

Rotational energy transfer cross sections are determined for NO (A ²Σ⁺, v' = 0, N' = 0, 7, and 15) +He and NO (A ²Σ⁺, v' = 0, N' = 0) +Ar by the two-color, double-resonance ionization method. Rotational jumps up to ΔN' = 8 take place as a single collision event. The cross sections determined are discussed in terms of the IOS and ECS scaling laws.     

Steric effect in the energy transfer reaction of oriented CO (a 3Π, v'=0, Ω=1 and 2) + NO (X 2Π) → NO (A 2Σ+, B 2Π) + CO (X 1Σ+)

The oriented CO (a (3)Π, v' = 0, Ω = 1 and 2) beam has been prepared by using an electric hexapole and applied to the energy transfer reaction of CO (a (3)Π, v' = 0, Ω = 1 and 2) + NO (X (2)Π) → NO (A (2)Σ(+), B (2)Π) + CO (X (1)Σ(+)). The emission spectra of NO (A (2)Σ(+), B(2)Π) have been measured at three orientation configurations (C-end, O-end, random). The shape of the emission spectra (and/or the internal excitation of products) turns out to be insensitive to the molecular orientation. The vibrational distributions of NO (A (2)Σ(+), v' = 0-2) and NO (B (2)Π, v' = 0-2) are determined to be N(v'=0):N(v'=1):N(v'=2) = 1:0.40 ± 0.05:0.10 ± 0.05 and N(v'=0):N(v'=1):N(v'= 2) = 1:0.6 ± 0.1:0.7 ± 0.1, respectively, and the branching ratio γ/β [=NO (A (2)Σ(+))/NO (B (2)Π)] is estimated to be γ/β ～ 0.3 ± 0.1 by means of spectral simulation. These vibrational distributions of NO (A, B) can be essentially attributed to the product-pair correlations between CO (X, v″) and NO (A (2)Σ(+), v' = 0-2), NO (B (2)Π, v' = 0-2) due to energetic restriction under the vibrational distribution of CO (X, v″) produced from the vertical transition of CO (a (3)Π, v' = 0) → CO (X, v″) in the course of energy transfer. The steric opacity function has been determined at two wavelength regions: 220 < λ < 290 nm [NO (A → X) is dominant]; 320 < λ < 400 nm [NO (B → X) is dominant]. For both channels NO (A (2)Σ(+), B(2)Π), a significant CO (a (3)Π) alignment effect is recognized; the largest reactivity at the sideways direction with the small reactivity at the molecular axis direction is observed. These CO (a (3)Π) alignment effects can be essentially attributed to the steric asymmetry on two sets of molecular orbital overlap, [CO (2π) + NO (6σ (2π))] and [CO (5σ) + NO (1π (2π))]. All experimental observations support the electron exchange mechanism that is operative through the formation of a weakly bound complex OCNO.     

Ab initio study of electronic energy transfer in the quenching of CO*(a 3Π) by H2

Potential energy calculations for the interaction of CO(a ³Π) with H₂(X ¹Σ_g⁺) are presented, both at the MC SCF level and with the inclusion of extensive configuration interaction. In C_2v geometry, the lowest two ³B₂ surfaces exhibit a strongly avoided crossing. At the highest level of theory used, the lowest surface provides a barrier-free adiabatic pathway for energy transfer from CO(a) to H₂, the products being CO(X ¹Σ⁺) and H₂(b ³Σ_u⁺), which dissociates to two H atoms. The energy transfer occurs by a two-electron exchange mechanism.     

High-resolution spectroscopy on the B2Σ+,ν' = 0→X2Π, ν″ =1 transition in SiCl

High-resolution laser-induced fluorescence spectra of²⁸Si³⁵Cl and ²⁸Si³⁷Cl have been observed in a molecular beam. Accurate constants describing the rotational structure in the X ²Π, ν″ = 1 as well as in the electronically excited B ²Σ⁺, ν' = 0 state are given. An inverted fine structure was found in the excited state with a spin-splitting constant γ = −31.15±0.19 MHz for Si³⁵Cl and γ = −30.62 ±0.61 MHz for Si³⁷Cl.     

The O((1)D) + H2 (X (1)Σ+, v, j) → OH(X (2)Π, v', j') + H((2)S) reaction at low collision energy: when a simple statistical description of the dynamics works

In this communication, we highlight that statistical approaches for chemical reactions describe reasonably well the low energy dynamics of the title process. Consequently, such methods prove to be valuable to compute rate constants from low to room temperatures. Results are compared with experiment and recent precise quantum wave packet calculations [J. Phys. Chem. A, 2009, 113, 5285].     

Laser-induced fluorescence detection of CH(X2Π) produced from the reaction of Ar(3p2,0) at thermal energy

CH (X ²Π) radicals have been observed from the reaction Ar(³P₂,₀) + CH₄→ CH (X) + H₂ + H + Ar by using a flowing afterglow apparatus coupled with laser-induced fluorescence. It has been found that only 3.5% of the available energy is convened into the vibrational energy of CH(X).     

Lowest energy electronic transition in aqueous Cl(-) salts: Cl(-) → (H2O)6 charge transfer transition

We use UV resonance Raman spectroscopy to probe the lowest energy allowed electronic transitions of aqueous solutions containing Cl(-) salts. We show that the waters hydrating the Cl(-) are involved in charge transfer transitions that transfer electron density from Cl(-) to the water molecules. These charge transfer transitions cause significant change in the H-O-H bond angle in the excited state, which results in a strong enhancement of the preresonance Raman intensity of the water bending modes. Our work gives the first insight into the lowest allowed electronic transition of hydrated Cl(-).     

Gas phase reactions of Cl2O with X−(D2O)n=0–4 (X = O,OD, O2, DO2, and O3)

The reactions of Cl₂O with the cluster ions X⁻(D₂O)_n=0–4 (X = O, OD, O₂, DO₂, and O₃) were studied in a He buffer gas at temperatures within the range 171–298 K and pressures of 0.27–0.51 Torr, using a flow-tube apparatus. All ions were found to react with Cl₂O at rates slower than predicted by the collision rate and the charge center was transferred from X⁻ to Cl⁻ or ClO⁻. The primary product ions Cl⁻(DOCl) and ClO⁻(DOCl) were observed to react further to produce the ions Cl₃O⁻ and Cl₃O₂⁻. The rate constants for the observed reactions are reported and the role that thermodynamics plays in determining possible reaction channels is discussed.     

Kinetics of the N-Monoalkylation of Aniline with Methanol Over Zn1?XCoXFe2O4 (X = 0, 0.2, 0.5, 0.8 and 1.0)-Type Systems

The kinetics of regioselective dichlorocyclopropanation of 4-vinyl-1-cyclohexene has been studied under controlled phase transfer catalysis conditions, using aqueous sodium hydroxide as the base and 2-benzylidine-N,N,N,N,N,N-hexaethylpropane-1,3-diammonium dibromide (Dq-Br) as a new phase transfer reagent. The reaction was carried out at 40 °C under pseudo-first order conditions by employing aqueous sodium hydroxide and chloroform in excess and was monitored by gas chromatography. The effect of various experimental parameters on the rate of the reaction has been studied and based on the experimental results, a suitable mechanism is proposed.     

Temperature dependence of vibrational energy transfer in liquids: VV relaxation of CO(ν = 1) by O2 in liquid Ar from 86 to 145 K

The rate constant for the energy transfer process

has been measured for CO and O₂ dilute in liquid Ar along the coexistence curve between 86 and 145 K. The results are compared to gas phase measurements of this rate constant over the same temperature range. The ratio of the rate constants in the two phases is compared to that predicted by an application of the isolated binary collision (IBC) model for energy trasnfer, which scales the energy transfer rate constants by the rate constants for binary collisions in the two phases. The theoretical predictions of the IBC model are that the liquid state energy transfer rate constant, k^ℓ, should be 30–60% greater than the gas phase energy transfer rate constant, k^g. The measured value of k^ℓ is, within the experimental error, equal to that for k^g. Possible reasons for the discrepancy are discussed.     

Collisional quenching of NO(B2Πr)υ′ = 0 produced by the reaction of N(2D) with N2O

The reaction of N(²D) with N₂O has been used as a source of NO(B²Π_r)υ′= 0. The effects of added gases on its emission have been used to determine quenching rate coefficients (using a radiative lifetime of 3 × 10⁻⁶ s). These coefficients have been compared with rate coefficients for quenching the isoenergetic species NO(A²Σ⁺)υ′= 0,1.     

Rapid collisional quenching of the N = 1, υ = 2 level of the H2(c3Πu) metastable state by H2

The rate coefficient for collisional quenching of the N = 1, υ = 2 level of the H₂(c³Π_u) metastable state by H₂ is measured to be (2.0 ± 0.2)×10⁻¹⁵ m³/s at 300 K. The metastables are produced by an electric discharge, radiatively quenched by a pulsed laser, and the recovery of metastable population monitored by cw dye laser absorption.     

The formation of Pt(P–P)(X)(COAr) (X=Cl, I; Ar=Ph, 2-Tioph) complexes via insertion of carbon monoxide

Pt(diphosphine)X(aryl) complexes [diphosphine = 1,3-bis(diphenylphosphino)propane (dppp); aryl=phenyl, 2-thiophenyl; X=Cl, I] have been reacted with carbon monoxide in chloroform. It has been revealed by in situ NMR studies that the starting compounds insert carbon monoxide into the Pt-aryl group resulting in Pt(diphosphine)X{C(O)aryl} complexes. It has been found that the phenyl complexes are much more reactive than the corresponding 2-thiophenyl complexes. Similarly, higher reactivity has been observed with iodo than with the chloro complexes.     

Dynamics of X+CH4 (X=H,O,Cl) reactions: how reliable is transition state theory for fine-tuning potential energy surfaces?

Trajectory calculations run on global potential energy surfaces have shown that the topology of the entrance channel has strong implications on the dynamics of the title reactions. This may explain why huge differences are observed between the rate constants calculated from global dynamical methods and those obtained from local methods that employ the same potential energy surfaces but ignore such topological details. Local dynamics approaches such as transition state-based theories should then be used with caution for fine-tuning potential energy surfaces, especially for fast reactions with polyatomic species since the key statistical assumptions of the theory may not be valid for all degrees of freedom.     

The mechanism and kinetics of energy transfer processes in Xe–CCl4–M (M=CO,CO2) mixtures irradiated by xenon resonance light

The mechanism and kinetics of energy transfer from the Xe(6s[3/2]₁) resonance state to CO and CO₂ molecules have been investigated by XeCl(B–X) (λ_max=308 nm) fluorescence intensity measurements at stationary conditions in Xe–CCl₄–M systems. Steady-state analysis of the fluorescence intensity dependence on the xenon and M pressure at constant CCl₄ concentration shows that these processes occur in two- and three-body reactions: Xe(6s[3/2]₁⁰)+M→products; Xe(6s[3/2]₁⁰)+M+Xe→products. The two-body rate constants for above reactions have been found to be (0.7±0.2)×10⁻¹⁰ and (4.9±0.4)×10⁻¹⁰ cm³ s⁻¹ for CO and CO₂, respectively. The three-body rate constants have been found to be (3±1)×10⁻²⁹ and (2.4±0.3)×10⁻²⁸ cm⁶ s⁻¹ for CO and CO₂, respectively. It has been shown that the third order reaction is a very effective channel of xenon excited atoms decay at high xenon pressures (P(Xe)>50 Torr).     

Studies on the Intramolecular Inclusion Complexes of Functionalized Calixarenes with CH_3X (X=CN, NO_2)

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Synthesis and crystal structures of π complexes of copper(I) halides with diallyl disulfide 2CuX · DADS (X = Cl, Br; DADS = CH2=CH-CH2-S-S-CH2-CH=CH2)

Compounds 2CuCl · DADS (I) and 2CuBr · DADS (II) (DADS is diallyl disulfide) are prepared by the ac electrochemical synthesis, and their crystal structures are determined. The complexes are isostructural, space group P2₁/n, Z = 4; I: a = 8.995(2) Å, b = 12.541(2) Å, c = 9.644(2) Å, β = 98.74(2)°, V = 1075.3(4) ų, II: a = 9.064(2), b = 12.878(3), c = 9.832(2) Å, β = 98.61(3)°, V = 1134.7(4) ų. In complexes I and II, the tetradentate DADS ligand is chelate-bridging and is coordinated by two crystallographically independent copper atoms of two inorganic Cu₄X₄ fragments. An insignificantly distorted tetrahedral environment of each of the two copper atoms consists of the olefin group, sulfur atom, and two halogen atoms. The complexes are stabilized additionally by the formation of C-H?S hydrogen bonds involved in characteristic seven-membered rings in the structures.