Vibrational energy transfer in CH3I

Previous works have reported vibration—vibration and vibration—translation transfer rates in the methyl halides. Using the technique of laser induced infrared fluorescence we have studied energy transfer in the concluding member of this series, CH₃I. Following excitation by resonant lines of a Q-switch CO₂ laser, infrared fluorescence has been observed from the v₂, v₅ as well as the 2v₅, v₁, v₄ vibrational energy levels of CH₃I. All the observed states exhibit a single exponential decay rate of 23 ± 2 ms^?1 torr^?1. Measurements have also been made on deactivation of the various modes by rare gases. The risetime of the v₂, v₅ levels was found to be approximately 101 ± 20 ms^?1 torr^?1, while that of the 2v₅, v₁, v₄ levels was approximately 225 ± 45 ms^?1 torr^?1. Fluorescence was not detected from the v₃ level. These results are discussed in terms of SSH type theoretical calculations, and comparison is made with the results obtained for other members of the methyl halide series, namely CH₃F, CH₃Cl and CH₃Br.     

Unexpected frequency shifts and linewidth changes for rovibrational lines in the infrared emission spectra of CO2 excited by active nitrogen

Fourier transform emission spectra from flowing CO₂ excited by active nitrogen have been recorded in the 4.5 μm region, with a resolution of 0.0054 cm⁻¹, for different time intervals between the mixing of the two gases and observation of the emission. Significant frequency shifts (reaching 30 times the absolute uncertainty of the experimental frequencies) and linewidth changes are observed depending on the time interval and the value of the quantum number v₃, for thousands of rovibrational lines belonging to v₁v¹₂v₃ → v₁v¹₂(v₃-1) vibrational transitions.     

A laser induced fluorescence study of vibrational energy transfer processes in cyclopropane

Results of infrared laser induced fluorescence studies on cyclopropane are presented. Molecules were excited from the ground state to the v₁₀ level of cyclopropane using a Q-switched CO₂ laser operating on either the P(14) or P(20) transition of the 9.6 μ branch. Fluorescence was observed from the v₆, v₈, v₁₀ + v₁₁ and v₅ + v₁₀ levels of cyclopropane. The self-deactivation of vibrationally excited cyclopropane through V → T/R processes was found to have a rate of 8.0 ± 1.5 ms^?1 torr^?1. Deactivation by rare gas collisions was also studied with comparison to simple V → T and V → R theories. V → V equilibration processes are discussed involving the v₆, v₈, v₁₀, v₁₁, and v₁₀ + v₁₁ levels.     

The electronic structures of tetrahedral oxo-complexes. The nature of the “charge transfer” transitions

The electronic structures of MnO^?₄, MnO^2?₄, MnO^3?₄, CrO^2?₄, CrO^3?₄, VO^3?₄, RuO₄, RuO^?₄, RuO^2?₄, TcO^?₄ and MoO^2?₄ have been investigated using the Hartree-Fock-Slater Discrete Variational Method. The calculated ordering of the valence orbitals of all the comlexes is: t₁, 4t₂, 3a₁, 1c, 3t₂, with t₁ the orbital of highest energy. The calculated single transition energies are in good agreement with experimental values and indicate the uniform assignment: t₁ → 2e(v₁), 4t₂ → 2e(v₂). t₁ → 5t₂(v₃), and 4t₂ → 5t₂(v₄). A/D values, calculated from the theory of magnetic circular dichroism (MDC) also support this assignment.Population analyses reveal that all complexes, whether d⁰, d¹ or d², have d-orbital populations close to those of the corresponding M²⁺ ions in which two electrons have been removed from the (n + 1)s orbital of M. This is also true of the excited states, such as t₁ → 2e and 4t₂ → 2e, where a transfer of charge from the ligands to the metal has previously been assumed. It is shown that, instead of a transfer of charge from ligands to metal, electronic excitation consists of a rearrangement of electron density both at the ligands and at the metal.     

Detailed electron spectrometric study of the ionization of H2 by He* (21 S, 23 S)

The energy spectra of electrons released in thermal energy (≈ 50 meV) ionizing collisions of He*(2¹ S, 2³ S) with H₂ have been measured with high resolution and low background. Based on a detailed data analysis, we report accurate H ₂ ⁺ (v′) vibrational populationsP(v′) for both He*(2¹ S)+H₂(v′=0–10) and He*(2³ S)+H₂(v′=0–15) and the spectral shapeS(ε) for the individual vibrational peaks. The vibrational populationsP(v′) are quite similar to the Franck-Condon factorsf _v ′0 for unperturbed H₂(v″=0)→H ₂ ⁺ (v′) transitions, but, more in detail, the ratiosP(v′)/f _v ′0 show a characteristically differentv′-dependence for He*(2³ S), He*(2¹ S), and HeI_α(58.4 nm) ionization. The vibrational level separations in the He*(2¹ S, 2³ S)+H₂ spectra agree with those in the HeI photoelectron spectrum to within 1–2 meV. The spectral shapesS(ε) are characteristically different for He*(2¹ S)+H₂ and He*(2³ S)+H₂, reflecting the respective differences in the entrance channel potentials, as determined previously in ab initio calculations and from scattering experiments.     

A new approach to electron diffraction analysis of symmetric triatomic molecules with large-amplitude bending motion: The equilibrium geometry,force field and vibrational frequencies of BaI2 as determined by electron diffraction

Diffraction data on BaI₂, analyzed by a new approach, indicate an anharmonic potential with a barrier of 71(12) cm^?1 at a linear geometry. The structural and vibrational parameters were found to be r_e^h(Ba-I_o) = 3.150(7)Å, ∠_eIBaI = 148.0(9) °, f_q = 0.69(8) mdyn/Å,f_qq= 0.14(6) mdyn/Å, k₂ = ?0.0075(15) mdyn/Å, k₄ = 0.0025(9) mdyn/ų, v₁ = 106(12) cm^?1 and v₃ = 145(21) cm^?1. The bending frequency v₂ is predicted to be near 16 cm^?1.     

HF(B1Σ→X1Σ) UV chemiluminescence from the H+/H+2+F− ion-ion reactions

Chemiluminescence spectra attributable to the H⁺/H⁺₂+F⁻→ HF B¹Σ ion-ion reactions were obtained in the wavelength region 185–270 nm. The rovibrationally resolved bands were assigned as HF B ¹Σ (v', J') to HF X ¹Σ (v″,J″) transitions with 0⩽v'⩽4 and 12 ⩽ v″ ⩽ 16. The corresponding rotational branches all have peaks at high J values. These non-thermal distributions suggest that the corresponding product state v',J' populations reflect the nascent distribution from the ion-ion reactions.     

Combined analysis of microwave and infrared spectra of methyl iodide: rotational and l-type doubling constants of the v5, v3+v6 and v2 states

The rotational constant B and the l-type doubling constant q were determined for the v₅, v₃+v₆ and v₂, states of CH₂I from the microwave transition frequencies, in combination with the infrared data previously reported. Since these vibrational states were coupled through the Fermi resonance and the xy-type E-E and A₁-E Coriolis resonances, the analysis was made by setting up and solving the complete form of the secular determinants of the energy matrices. The rotational and l-type doubling constants were determined as B₅, = 0.250 173 cm^?1, B₃₆ = 0.247 600 cm^?1, B₂ = 0.249 369 cm^?1, q₅ = ?0.000 027 cm^?1 and q₃₆ = ?0.000 179 cm^?1, which are unperturbed by Fermi and Coriolis interactions. Other band constants for v₅ and v₃+v₆ were also refined in accordance with the new values of B₅ and B₃₆. The present study indicated that the combined analysis of microwave and infrared spectral data was useful for the precise determination of vibration-rotation, levels in the perturbed system.     

Quasi-resonant energy transfer in collisions: Na2(A1Σ u + )+K(4S)

Cross sections for electron energy transfer from the initial rotational stateJ′of the two lowest vibrational levelsv′=0 andv′=1 of excited dimers Na₂(A) to potassium atoms as described by Na₂(A¹Σ _u ⁺ ,v′J′)+K(4S)→Na₂ (X¹Σ _g ⁺ ,v″J″)+K(4P)+ΔE have been examined by laser-induced fluorescence. A strong increase of the cross section by as much as an order of magnitude has been observed for those dimerv′J′-levels for which the dipole transitions are close to resonance of the 4S-4P transitions in the atom (ΔE<4 cm^?1). The absolute cross sections for energy transfer have been calculated by the Rabitz approximation of first-order perturbation theory. In the case of closest energy resonance (ΔE=0.9 cm^?1) the cross section is Q=7.8×10^?13 cm².     

Vibrational relaxation of NH2|X2B1(O,v2, O)| radicals

Energy transfer processes in NH₂ radicals have been studied using the sensitive laser-induced fluorescence (LIF) technique. The NH₂ radicals were generated by infrared multiple-photon dissociation (IR MPD) of monomethylamine (CH₃NH₂), and the state-selected NH₂(v″₂ = 1) decay was observed by the LIF detection of [NH²]. The vibrational relaxation processes studied are NH₂(v″₂ = 1) + M → NH₂(v″₂ = O)+M, with M  He, Ne, Ar, Kr, H₂, D₂, CO, O₂, and total decay rate of NH₂(v″₂ = 1) in the presence of excess of CH₃NH₂. Rate constants of (3.41±0.03)×10⁻¹³, (1.75±0.09)×10⁻¹³, (3.03±0.08)× 10⁻¹³, (3.58±0.06)×10⁻¹³, (13.4±0.5)×10⁻¹³, (4.70±0.19)×10⁻¹³, (4.3±0.3)×10⁻¹³, (5.9±-0.4)×10⁻¹³, (9.2±0.5)×10⁻¹³), and 8.4×10⁻¹¹ cm³ molecule⁻¹ s⁻¹ were determined for the vibrational deactivation of NH₂(v″₂ = 1) by He, Ne, Ar, Kr, H², D₂, N₂, CO, O₂, and CH₃NH₂, respectively. The effect of the different collision partners on the relaxation rate is discussed. The results can be qualitatively well understood in terms of strong vibration—rotation coupling, due to the small moment of inertia of the NH₂ radicals.     

The electronic structure of FeO 4 2− , RuO4, RuO 4 − , RuO 4 2− and OsO4 by the HFS-DVM method

The electronic structures of FeO ₄ ^2? , RuO₄, RuO ₄ ^? , RuO ₄ ^2? and OsO₄ have been investigated using the Hartree-Fock-Slater Discrete Variational Method. The calculated ordering of the valence orbitals is 2t ₂, 1e, 2a ₁, 3t ₂ andt ₁ with thet ₁ orbital as the highest occupied. The first five charge transfer bands are assigned as:t ₁→2e(v ₁), 3t ₂→2e(v ₂),t ₁→4t ₂(v ₃), 3t ₂→4t ₂(v ₄) and 2a ₁→4t ₂(v ₅). It is suggested that ad-d transition should be observed at 1.5 eV in RuO ₄ ^? and RuO ₄ ^2? .     

Effect of the activation of a graphite-epoxy composite electrode and the buffer capacity of a solution on the reversibility of the hydroquinone electrode reaction

Peak potentials and the kinetics of hydroquinone oxidation at an electrode from a graphite-epoxy composite in activated and passivated states were studied in supporting electrolytes of different buffer capacities and pH varying from 0.1 to 8.8, using methods of direct-current and cyclic voltammetry. The electrode was activated before its polarization by mechanically cutting a 0.2–4-μm surface layer directly in a test solution. The electrode was passivated by storing in air for two or more days. The behavior of hydroquinone in its oxidation at the passivated and activated electrodes was compared using diagnostic criteria for the following functions: I _a?v ^1/2, logI _a?logv, I _a/v ^1/2?v ^1/2, and I _a/c, where v is the rate of the potential sweep and c is the volumetric concentration of hydroquinone. The potential difference of anodic and cathodic peaks in cyclic voltammograms indicated the reversibility of the electrode reaction in all supporting electrolytes.     

Jahn—Teller effects in the mindo approximation: structures of the molecular cations of methane and the chloromethanes

The MINDO/3 technique gives geometries for (CH₄)⁺, (CCl₄)⁺ and the intermediate ions (CH_nCl_{4 ? n})⁺ (n = 1, 2, 3) which have symmetries in precise accord with the predictions of the Jahn—Teller effect. The ground state of (CH₄)⁺ has D_2d symmetry, with a C_3v structure ca. 45.6 kJ mol^?1 higher. (CCl₄)⁺ has a C_2v ground state, with a D_2d structure ca. 144 kJ mol^?1 higher: no bound state of C_3v symmetry could be found. (CH₃Cl)⁺ and (CHCl₃)⁺ both have C_s symmetry, and (CH₂Cl₂)⁺ has C_2v symmetry. The analogous fluoro ions are discussed briefly.     

LC Determination and Pharmacokinetic Study of Sinomenine in Dog Plasma

A simple HPLC method has been developed for determination of sinomenine in dog plasma and has been used to evaluate the pharmacokinetics of sinomenine tablets in dogs. Chromatographic separation was performed on a reversed-phase column with 0.78% (w/v) NaH₂PO₄-acetonitrile, 88:12 (v/v), as mobile phase, delivered at a flow rate of 1.5 mL min^?1. Detection was performed at 265 nm. The limit of quantification was 5.0 ng mL^?1. The calibration range was from 5.0 to 1000 ng mL^?1. The developed method was applied to pharmacokinetic studies of sinomenine sustained-release tablets (test preparation) and sinomenine conventional tablets (reference preparation) in six dogs. Pharmacokinetic data t _max, C _max, AUC _0-t , AUC _0-∞, and t _1/2 for both preparations were determined from plasma concentration-time profiles. The method was sufficiently sensitive, simple, and repeatable for use in pharmacokinetic studies.     

Force constants,vibrational assignment and geometry of methyl amine from hartree—fock calculations

The force constants and geometry of CH₃NH₂ have been calculated from Hartree—Fock wave-functions by the force method, using a 73/3/1 Gaussian basis set. The fundamental frequencies obtained from the ab initio force constants corroborate the assignment of Gray and Lord except for the uncertain A″ NH₂ twisting and CH₃ rocking frequencies. The results indicate that the 1335 cm^?1 band in CH₃NH₂ is v₁₃, the antisymmetric combination of these modes, and that their symmetric combination, v₁₄, is located between 880 and 1000 cm^?1. The calculations reproduce the experimentally observed tilting of the CH₃ group toward the lone pair on nitrogen.     

Model calculations of the vibrations of bonded water molecules

Model calculations have been made of the vibrational frequencies and normal modes of a water molecule vibrating in a combined internal and external field. A constant internal force field has been used together with an external central force field from four or three nearest-neighbour atoms to the water molecule. These neighbour atoms have been arranged either tetrahedrally or trigonally around the water molecule. The external force field has been further restricted by the use of five possible site symmetries for the water molecule, C_2v, C₂, C_s(σ_xz, C_s(σ_yz) and C₁. A series of calculations have been made where the external force constants have been varied within the range 1—80 Nm^?1.The nine calculated normal modes can be divided into three groups: intra-molecular, rotational and translational vibrations. Among the rotational vibrations it is found that, in the tetrahedral environment, the rocking mode occurs at lower frequencies than the twisting and wagging modes, whereas the opposite occurs for the trigonal environment. Frequency ratios have been calculated using the isotopic species H₂O, D₂O, HDO and H,¹⁸O. The twisting and wagging modes have the vH₂O/vD₂O ratio in the range 1.35-3-1.41 and the rocking mode in the range 1.26—1.41.     

O-atom transfer biomimetic oxidation of benzoin in the presence of monooxomolybdenum(IV) thiolate complexes

Novel catalytically active monooxomolybdenum(IV) species containing four thiolate ligands obtainable in solution by NaBH₄ reduction of [Mo^vO(SC₆H₅)₄]⁻, [Mo^vO(Z-cys-Val-OMe)₄]⁻, (Z=benzyloxycarbonyl), or [Mo^vO(S₂C₆H₄)₂]⁻ perform the pyridine-N-oxide oxidation of benzoin in N,N-dimethylformamide at 30 °C. The order of catalytic activity is [Mo^vO(Z-cys-Val-OMe)₄]⁻ > [Mo^vO(S₂C₆H₄)₂]⁻ > [Mo^vO(SC₆H₅)₄]⁻ ([benzoin]/[oxidant]/[catalyst]= 20/20/1), while the oxidation by air under the same catalytic conditions gives a different order, [Mo^vO(Z-cys-Val-OMe)₄]⁻> [Mo^vO(SC₆H₅)₄]⁻ >[Mo^vO(S₂C₆H₄)₂]⁻. During the catalytic cycle in the amine-N-oxide oxidation, two intermediate species, [Mo^IVOL₄]²⁻ and [Mo^VIO₂L₄]²⁻, were detected by ¹H NMR, while in the air oxidation an unidentified Mo(VT) species is involved.     

Hyperfine structure measurements in the B3IIo+u—X 1Σ+g electronic transition of Br2

Hyperfine splittings in some band heads of the B—X system of Br₂ were measured using laser molecular-beam spectroscopy. Quadrupole coupling constants were derived: eqQ(⁷⁹Br) = 810.0(5) MHz for X¹Σ⁺_g, v = 1, and eqQ(⁷⁹Br) = 179.1(16) MHz for B³πino⁺u, v' = 13.     

The emission spectrum of the 1B1(π*-n+) state of 1,2-cyclobutanedione excited at 488.0 nm

The spectrum of the emission from the ¹B₁(π^*-n₊) state of 1,2-cyclobutanedione excited at 488.0 nm has been measured. Wavelengths and vibrational assignments are reported for 24 bands between 490 and 550 nm, 12 of which can be identified with hot bands in the absorption spectrum. Prominent bands in the emission spectrum are associated with excitation of V^''₈, the symmetric in-plane carbonyl bend (281 cm⁻¹); v^''₁₂, the asymmetric carbonyl wag (488 cm⁻¹); and v^''₇, a symmetric ring distortion (522 cm⁻¹). Sequences in v₁₃, the ring-twisting vibration, are also prominent; the initial excitation lies in the 13³₃ absorption band, while the emission shows intensity maxima for v^'₁₃ = 0 and 2, and a bimodal vibrational relaxation is suggested.     

Volumetric, viscometric and refractive index behavior of some α-amino acids in aqueous tetrapropylammonium bromide at different temperatures

Densities, ρ, viscosities, η, and refractive indices, n _D, of glycine (Gly), DL-alanine (Ala), DL-valine (Val) (0.05, 0.10, 0.15, 0.20, 0.25 mol kg^?1), and L-leucine (Leu) (0.02, 0.05, 0.10 mol kg^?1) in water and in 0.20 mol kg^?1 aqueous tetrapropylammonium bromide (TPAB) have been measured at 298.15, 303.15, 308.15, and 313.15 K. The density data have been utilized to calculate apparent molar volumes, ?_v, partial molar volumes at infinite dilution, ?_v°, and partial molar volumes of transfer, ? _v°(tr) of amino acids. The viscosity data have been analyzed by means of Jones-Dole equation to obtain Falkenhagen coefficient, A, and Jones-Dole coefficient, B, free energy of activation of viscous flow per mole of solvent, Δµ₁°*, and solute, Δµ₂°*, and enthalpy, ΔH*, and entropy of activation, ΔS*, of viscous flow. The refractive index data have been used to calculate molar refractivity, R _D, of amino acids in aqueous tetrapropylammonium bromide solutions. It has been observed that ?_v°, B-coefficient and Δµ₂°* vary linearly with increasing number of carbon atoms in the alkyl chain of amino acids, and they were split to get contributions from the zwitterionic end groups (NH₃ ⁺, COO^-) and methylene group (CH₂) of the amino acids. The behavior of these parameters has been used to investigate the solute-solute and solute-solvent interactions as well as the effect of tetrapropylammonium cation (C₃H₇)₄N⁺ on these interactions.