Spin-orbit quenching of Cl(2P(1∕2)) by H2

We report fully-quantum, time-independent, scattering calculations for the spin-orbit quenching of Cl((2)P(1∕2)) by H(2) molecules at low and moderate temperature. Our calculations take into account chemical reaction channels. Cross sections are calculated for total energies up to 5000 cm(-1) which are used to determine, by thermal averaging, state-to-state rate coefficients at temperatures ranging from 50 to 500 K. Spin-orbit relaxation of chlorine is dominated by collisions with H(2) in the rotationally excited states j = 2 and j = 3. In the former case the near-resonant energy transfer is the primary relaxation mechanism. The inclusion of the reactive channel could lead differences compared to pure inelastic calculations. Good agreement is obtained with experimental relaxation measurements at room temperature.     

Photodissociation of CS2+( 2 Πg) via (1+1) Excitation

Photodissociation dynamics of CS2+molecular ions has been investigated by (1+two-photon resonance technique. CS2+were prepared by (3+1) resonance-enhanced multi-photon ionization (REMPI) of CS2molecules at 483. 2nm. The photofragment S+excitati (PHOFEX) spectra were recorded by scanning another laser in the 424~482nm region, and we assigned essentially to CS2+(~A2Πu,3/2(v′=0~4)←~X2Πg,3/2(0,0,0)) and (~A2Πu,1/2(v′=0,4)←~X2Πg,1/2(0,0,0)) (herev′=v1′+(1/2)v2′) transitions. The S+production channel wpreliminarily attributed to, (i) one-photon excitation CS2+from the ground state~X2Πgto texcited state~A2Πu; (ii) vibronic coupling between the~A2Πustate and the high vibrational lev in the~X2Πgstate; (iii) second photon excitation from the coupling vibrational levels to the excied state~B2Σu+and dissociation to produce S++ CS via the repulsive4Σ-state through spin-orb interaction between the~B2Σu+and4Σ-states.     

Excited-state dynamics of trans,trans-1,3,5,7-octatetraene: estimation of decay rate constants of 1(1)B(u) ⇝ 2(1)A(g) and 2(1)A(g) ⇝ 1(1)A(g) internal conversions

The general expressions we previously derived for calculating internal conversion rate constants between two adiabatic displaced-distorted-rotated potential energy surfaces, by including all vibratinal modes, are applied to estimate the decay rate constants of 1(1)B(u) ? 2(1)A(g) and 2(1)A(g) ? 1(1)A(g) internal conversions in trans,trans-1,3,5,7-octatetraene molecule. The minimal models with respect to the number and types of vibrational modes are determined for these processes. Our calculations show that in the low temperature limit the 1(1)B(u) ? 2(1)A(g) internal conversion takes place on a 232-290 fs time scale in the condensed phase and 2 ps in the gas phase, whereas 2(1)A(g) ? 1(1)A(g) internal conversion takes place on a 2 μs time scale under the isolated conditions.     

Ab initio Study of H2O–HCl (1:1, 1:2, 2:1) Complexes

This paper reports on an ab initio (6-31G**) study of 1:1, 1:2, and 2:1 (H₂O) _n (HCl) _m complexes. Stable configurations of the 1:2 and 2:1 (H₂O) _n (HCl) _m complexes and their geometrical and energy characteristics were determined. The vibrational analysis of the complexes was carried out. The effect of hydrogen bonding due to S₁S₀ and T₀T₁ electronic excitations is considered.     

The 1(5)Π(g) state of C2

We report ab initio spectroscopic constants for the recently identified 1(5)Π(g) state of C(2) [P. Bornhauser, Y. Sych, G. Knopp, T. Gerber, and P. P. Radi, J. Chem. Phys. 134, 044302 (2011)]. The calculations are performed at the multi-reference configuration interaction level of theory with Davidson's correction using aug-cc-pV6Z basis sets and include core-valence correlation and relativistic corrections obtained with quadruple-zeta bases. Such treatment accurately reproduces the experimentally observed constants of the a(3)Π(u) and other states. Thus, we expect our calculated ω(e) value for the 1(5)Π(g) state to be within a few cm(-1), and rotational constants to be within 0.1% of experiment. Agreement with available spectroscopic data is excellent, with the calculations strongly suggesting that the 1(5)Π(g) vibrational level observed by Bornhauser et al. is v = 0.     

Synthesis of nanopowders of pentoxides Ta2y Nb2(1−y)O5

The processes of production of high purity nanopowders of niobium and tantalum pentoxide Ta_2y Nb_2(1–y)O₅ with a low content of fluorine and Nb₂O₅ in low-temperature polymorph were studied. Ceramic samples were prepared from a charge of solid solutions LiTa _y Nb_1–y O₃ and Li _x Na_1–x Ta _y Nb_1–y O₃ synthesized using coprecipitated pentoxide Ta_2y Nb_2(1–y)O₅. Therewith for solid solutions LixNa_1–x Ta _y Nb_1–y O₃ significantly larger values of high dielectric constant and ionic conductivity were achieved compared to the solid solutions obtained by using a mechanical mixture of Ta₂O₅ and Nb₂O₅. This converts solid solutions LixNa_1–x Ta _y Nb_1–y O₃ from acoustoelectronic and piezoelectric type of materials into the capacitor and ion-conductive type of solid materials.     

Enzymatic α(1→2)-l-fucosylation: investigation of the specificity of the α(1→2)-l-galactosyltransferase from Helix pomatia

The α(1→2)-l-galactosyltransferase from Helix pomatia transfers an l-fucosyl residue from GDP-l-Fucose to a terminal, non-reducing d-galactopyranosyl moiety of an oligosaccharide. The extent of the enzyme's specificity towards the stereochemistry at the d-galactopyranosyl anomeric centre, the site of interglycosidic linkage and the nature of the subterminal oligosaccharide residue has been investigated using HPAEC-PAD and MALDI-TOF technology. This α(1→2)-l-galactosyltransferase is specific for d-galactopyranosyl β-linkages, independent of the site of the interglycosidic linkage and aglycone configuration and with limited specificity for the nature of the subterminal sugar residue.     

Synthesis of 2-(3-hydroxy-2-methyl-1-alkenyl)-1-pyrrolines and 2-(3-hydroxybutyl)-1-pyrroline using α-lithiated 2-methyl-1-pyrroline

Condensation of 2-methyl-1-pyrroline with chloroacetone or 3-chloro-2-butanone using LDA in THF afforded novel 2-(3-hydroxy-2-methyl-1-alkenyl)-1-pyrrolines via a peculiar reaction mechanism instead of the anticipated 2-(3-oxobutyl)-1-pyrrolines. The intermediacy of 2-(2,3-epoxy-2-methylalkyl)-1-pyrrolines in the latter transformation was demonstrated by immediate reductive epoxide ring opening utilizing lithium aluminium hydride in diethyl ether. Furthermore, 2-(3-oxobutyl)-1-pyrroline was prepared via an alternative approach through alkylation of 2-methyl-1-pyrroline with 3-chloro-2-(methoxymethyloxy)-1-propene using LDA in THF, followed by acid hydrolysis. Reduction of 2-(3-oxobutyl)-1-pyrroline by sodium borohydride in methanol afforded the corresponding 2-(3-hydroxybutyl)-1-pyrroline in good yield.     

Formation of Unsymmetrical 2-(Diacylmethylene)-2,3-dihydro-1H-benzimidazoles During Acidolysis of 1-Benzoyl-2-(β-benzoyloxy-β-phenylvinyl)-1H-benzimidazole

The reaction of 1-benzoyl-2-(-benzoyloxy--phenylvinyl)-1H-benzimidazole with carboxylic acids was investigated. A convenient method was developed for the synthesis of unsymmetrical 2-(diacylmethylene)-2,3-dihydro-1H-benzimidazoles. 2-(4-Pyrazolyl)-1H-benzimidazoles were obtained by the reaction of 2-(benzoylformylmethylene)-2,3-dihydro-1H-benzimidazole with hydrazine.     

Observation of photocatalytic dissociation of water on terminal Ti sites of TiO2(110)-1 × 1 surface

The water splitting reaction based on the promising TiO(2) photocatalyst is one of the fundamental processes that bears significant implication in hydrogen energy technology and has been extensively studied. However, a long-standing puzzling question in understanding the reaction sequence of the water splitting is whether the initial reaction step is a photocatalytic process and how it happens. Here, using the low temperature scanning tunneling microscopy (STM) performed at 80 K, we observed the dissociation of individually adsorbed water molecules at the 5-fold coordinated Ti (Ti(5c)) sites of the reduced TiO(2) (110)-1 × 1 surface under the irradiation of UV lights with the wavelength shorter than 400 nm, or to say its energy larger than the band gap of 3.1 eV for the rutile TiO(2). This finding thus clearly suggests the involvement of a photocatalytic dissociation process that produces two kinds of hydroxyl species. One is always present at the adjacent bridging oxygen sites, that is, OH(br), and the other either occurs as OH(t) at Ti(5c) sites away from the original ones or even desorbs from the surface. In comparison, the tip-induced dissociation of the water can only produce OH(t) or oxygen adatoms exactly at the original Ti(5c) sites, without the trace of OH(br). Such a difference clearly indicates that the photocatalytic dissociation of the water undergoes a process that differs significantly from the attachment of electrons injected by the tip. Our results imply that the initial step of the water dissociation under the UV light irradiation may not be reduced by the electrons, but most likely oxidized by the holes generated by the photons.     

Synthesis of derivatives of 2-aminoimidazole and 2-iminoimidazolidine by cyclization of 1-aryl-2-(4,6-dimethylpyrimidin-2-yl)guanidines with α-bromocarbonyl compounds

Cyclization of 1-aryl-2-(4,6-dimethylpyrimidin-2-yl)guanidines with α-bromoacetophenone and ethyl bromoacetate gave derivatives of 1,4-diphenyl-1H-imidazole-2-amine and 2-amino-1-phenylimidazolidin- 4-one respectively. The mechanism of the reaction was determined on the basis of quantum-chemical calculations, NOESY NMR spectroscopy, and X-ray crystallography.     

Samarium(Ⅱ) Iodide Promoted Synthesis of 1-ethoxycarbonylmethyl-2-hydrofullerene

The ethyl analog of the above compound has been reported before by severalgroupsg- I 1. For example Komatsu and coworkers synthesized C60(H)(CHZCOOEt) by aReformatsky-type of reaction, treating ethyl bromoacetate and zinc with C60 in avibrating mill without any solventg. Besides the main product C60(H)(CHZCOOEt),three other byproducts were also isolated including a l,4-dihydrofullerene derivativeC60(CHZCOOEt)2. The spectroscopic data of the present product confirm its structure asd…     

Two-photon (A1B2 ← X1 A1) supersonic jet spectrum of aniline

The supersonic jet multiphoton ionization (2 photons to resonance, 4 to ionization) ¹A ← ¹X spectrum of aniline is reported in the 560–590 nm region. The two-photon ¹A ← ¹X spectrum is very similar to the analogous one-photon spectrum. In particular, ν₁₄, the Kekulé signature mode of two-photon ¹L_b substituted benzene spectra is not prominent, but two quanta of the amino inversion mode, ν_I, are. A dispartiy between theoretical calculations of the ¹A ← ¹X two-photon cross-section, and the thermal lensing cross-section reported by Rice and Anderson [J. phys. Chem. 90, 6793 (1986)] is noted. The theoretical considerations only account for about half the thermal lensing intensity.     

Crossed beam reactions of methylidyne [CH(X2Π)] with D2-acetylene [C2D2(X1Σg(+))] and of D1-methylidyne [CD(X2Π)] with acetylene [C2H2(X1Σg(+))

The crossed molecular beam reactions of ground state methylidyne, CH(X(2)Π), with D2-acetylene, C(2)D(2)(X(1)Σ(g)(+)), and of D1-methylidyne, CD(X(2)Π), with acetylene, C(2)H(2)(X(1)Σ(g)(+)), were conducted under single collision conditions at a collision energy of 17 kJ mol(-1). Four competing reaction channels were identified in each system following atomic 'hydrogen' (H/D) and molecular 'hydrogen' (H(2)/D(2)/HD) losses. The reaction dynamics were found to be indirect via complex formation and were initiated by two barrierless-addition pathways of methylidyne/D1-methylidyne to one and to both carbon atoms of the D2-acetylene/acetylene reactant yielding HCCDCD/DCCHCH and c-C(3)D(2)H/c-C(3)H(2)D collision complexes, respectively. The latter decomposed via atomic hydrogen/deuterium ejection to form the thermodynamically most stable cyclopropenylidene species (c-C(3)H(2), c-C(3)D(2), c-C(3)DH). On the other hand, the HCCDCD/DCCHCH adducts underwent hydrogen/deuterium shifts to form the propargyl radicals (HDCCCD, D(2)CCCH; HDCCCH, H(2)CCCD) followed by molecular 'hydrogen' losses within the rotational plane of the decomposing complex yielding l-C(3)H/l-C(3)D. Quantitatively, our crossed beam studies suggest a dominating atomic compared to molecular 'hydrogen' loss with fractions of 81 ± 23% vs. 19 ± 10% for the CD/C(2)H(2) and 87 ± 30% vs. 13 ± 4% for the CH/C(2)D(2) systems. The role of these reactions in the formation of interstellar isomers of C(3)H(2) and C(3)H is also discussed.     

Sub-doppler two-photon spectrum of asymmetric rotor molecules: analysis of the qqQ rotational branch of the S1(1B2u)141 ← S0(1A1g) system of benzene-d1

The Doppler-free two-photon excitation spectrum of the ^qqQ branch of the 14¹₀ vibrational band of the S₁(¹B_2u) ← S₀(₁A_1g) transition of benzene-d₁ has been recorded using a cw single-mode dye laser coupled to an external concentric resonator. The spectrum has been analysed using a non-rigid Watson Hamiltonian. More than 200 lines with J up to 20 have been assigned and the rotational constants which best reproduce the spectrum are A¹_v = 0.181435, B¹_v = 0.169990, C¹_v = 0.089055 cm⁻¹. The K_a = odd lines of the ^qqQ₅(J) subbranch show small and quite regular perturbations of 60 ± 5 MHz which are probably due to a coupling to another vibrational state of the S₁ manifold.     

Inclusion compounds of (±) gossypol. Structure of the gossypol-n-valeric acid (1/2) coordinato-clathrate

The crystal structure of the inclusion compound of gossypol withn-valeric acid as a guest molecule has been determined by X-ray structure analysis. The crystals of C₃₀H₃₀O₈·(C₅H₁₀O₂)₂, are triclinic, space group ,a=6.912(2),b=14.506(3),c=19.387(4) Å, =78.85(2)°, =83.92(3)°, =86.78(3)°V=1895(1) ų,Z=2,D _x=1.267 g cm^–3, (CuK )=0.768 mm^–1,T=292 K. The structure has been solved by direct methods on intensity data collected for a twinned crystal and refined to the finalR value of 0.062 for 1606 observed reflections and 470 refined parameters.Gossypol-n-valeric acid (1/2) coordinato-clathrate is not isostructural with any of the previously investigated gossypol inclusion compounds but shows some structural similarities to gossypol-acetic acid (1/1). The host and one of the carboxylic acid molecules are connected via hydrogen bonds into molecular assemblies of a column type which are further bonded to centrosymmetric dimers of the secondn-valeric acid molecule. In effect, host and guest molecules are assembled into layer-type H-bonded aggregates. Structural features common to gossypol-n-valeric acid (1/2) and other earlier reported gossypol inclusion compounds are discussed.Supplementary Data relevant to this article have been deposited with the British Library under the number SUP 82194 (9 pages)     

Regioselective silylation of 5-(2′-hydroxyethyl)cyclopent-2-en-1-ol and 6-(2′-hydroxyethyl)cyclohex-2-en-1-ol

Herein we report regioselective and mild reactions for the tert-butyldimethylsilyl mono-protection of 5-(2′-hydroxyethyl)cyclopent-2-en-1-ol (2) and 6-(2′-hydroxyethyl)cycohex-2-en-1-ol (5) at the primary hydroxyl group or at the secondary allylic hydroxyl group. The different steric environment surrounding the secondary allylic and saturated primary alcohols is mainly invoked to rationalize the observed regioselectivity.     

Conductivities of 1∶1 salts in 2-cyanopyridine

Electrolytic conductivities of eight simple 11 electrolytes have been measured in dilute solutions of 2-cyanopyridine (2CNP) at 30°. Infinite dilution mobilities and association constants were calculated using the Fuoss-Hsia equation. With the exception of LiCF₃SO₃ all salts show very little association, consistent with the very high dielectric constant of 2CNP. The weak association which does occur is attributed to weak ion-solvent interactions. No evidence was found for triple ion formation. Conductivities of concentrated solutions of LiAsF₆ in 2CNP increase slowly with concentration reaching a maximum at a concentration of around 0.65 mol-dm^–3. These conductances are slightly lower than those in propylene carbonate which has a lower dielectric constant and a higher viscosity. Conductivities of concentrated LiAsF₆ solutions in 2CNP mixtures with acetonitrile vary monotonically, consistent with solution viscosities, and show no sign of the maximum commonly observed in mixed organic solvents.