Communication: direct angle-resolved measurements of collision dynamics with electronically excited molecules: NO(A2Σ+) + Ar

We report direct doubly differential (quantum state and angle-resolved) scattering measurements involving short-lived electronically excited molecules using crossed molecular beams. In our experiment, supersonic beams of nitric oxide and argon atoms collide at 90°. In the crossing region, NO molecules are excited to the A(2)Σ(+)state by a pulsed nanosecond laser, undergo rotationally inelastic collisions with Ar atoms, and are then detected 400 ns later (approximately twice the radiative lifetime of the A(2)Σ(+)state) by 1 + 1(') multiphoton ionization via the E(2)Σ(+) state. The velocity distributions of the scattered molecules are recorded using velocity-mapped ion imaging. The resulting images provide a direct measurement of the state-to-state differential scattering cross sections. These results demonstrate that sufficient scattering events occur during the short lifetimes typical of molecular excited states (～200 ns, in this case) to allow spectroscopically detected quantum-state-resolved measurements of products of excited-state collisions.     

Picosecond and nanosecond kinetic spectroscopic investigations of the relaxation and the solute—solvent reaction of electronically excited 3,5-dinitroanisole

We investigated the relaxation of electronically excited nitro aromatic compounds, in particular 3,5-dinitroanisole (3,5-DINA), by means of picosecond and nanosecond laser kinetic spectroscopy. Complete neglect of differential overlap/spectroscopic—configuration interaction calculations were performed to characterize their excited states. The gas phase UV spectrum of 3,5-DINA and the electron spin resonance spectrum of the anion serve the same purpose. It is shown by means of IR spectroscopy that 3,5-DINA in its ground state does not form hydrogen bonds. The envelope of the first absorption band of 3,5-DINA in liquid solutions covers a weak nπ* and a strong ππ* transition. In non-hydrogen-bonding solvents, excitation in this band populates a primary excited state S_i which decays within 10 ps to S₀ and to T₀. The state T₀ (in CH₃CN) is converted within 780 ps to S₀. In hydrogen bonding solvents the decay is quite different. The conversion T₀ → S₀ and probably S_i → S₀ is much slower, while the intersystem crossing S_i → T₀ remains very fast. We conclude that in aprotic solvents both S_i and T₀ are nπ* states in which the excitation is localized on the NO₂ groups, which are consequently distorted to a large extent relative to the ground state. The distortion is thought to cause strong phonon coupling in the radiationless transitions S_i → S₀ and T₀ → S₀. Local vibrations in the NO₂ group, which modulate the overlap of lone pair orbitals on adjacent oxygen atoms, are efficient promoting modes in the radiationless decay and they make the rate constant much larger than in other cases involving local excitation of small chromophores, e.g. ketones. The primary state populated by excitation with our pulsed lasers is a ππ^* chare transfer state. When 3,5-DINA is brought into this state in hydrogen bonding solvents, it forms a (single) hydrogen bond before any other types of relaxation. Thus S_i and T₀ are both hydrogen-bonded delocalized ππ^* states. The known efficient bimolecular photo-induced reactions of 3,5-DINA involve the formation of the hydrogen bond as the first step. A reinterpretation is given of the variation in the triplet lifetime of 3,5-DINA over three orders of magnitude with solvent composition. The thermal dissociation of the hydrogen bond to the NO₂ group is the rate-determining step in the decay of 3,5-DINA in hydrogen bonding solvents. Both the activation energy and the activation entropy of this reaction depend on the solvent structure.     

Formation of acridones by ethylene extrusion in the reaction of arynes with β-lactams and dihydroquinolinones

N-Unsubstituted β-lactams react with a molecule of aryne by insertion into the amide bond to form a 2,3-dihydroquinolin-4-one, which subsequently reacts with another molecule of aryne to form an acridone by extrusion of a molecule of ethylene. 2,3-Dihydroquinolin-4-ones react under the same reaction conditions to afford identical results. This is the first example of ethylene extrusion in aryne chemistry.     

A crossed beam and ab initio investigation of the reaction of boron monoxide ((11)BO; X(2)Σ+) with acetylene (C2H2; X(1)Σ(g)+)

The reaction dynamics of boron monoxide (BO; X(2)Σ(+)) with acetylene (C(2)H(2); X(1)Σ(g)(+)) were investigated under single collision conditions at a collision energy of 13 kJ mol(-1) employing the crossed molecular beam technique; electronic structure RRKM calculations were conducted to complement the experimental data. The reaction was found to have no entrance barrier and proceeded via indirect scattering dynamics initiated by an addition of the boron monoxide radical with its boron atom to the carbon-carbon triple bond forming the O(11)BHCCH intermediate. The latter decomposed via hydrogen atom emission to form the linear O(11)BCCH product through a tight exit transition state. The experimentally observed sideways scattering suggests that the hydrogen atom leaves perpendicularly to the rotational plane of the decomposing complex and almost parallel to the total angular momentum vector. RRKM calculations indicate that a minor micro channel could involve a hydrogen migration in the initial collision to form an O(11)BCCH(2) intermediate, which in turn can also emit atomic hydrogen. The overall reaction to form O(11)BCCH plus atomic hydrogen from the separated reactants was determined to be exoergic by 62 ± 8 kJ mol(-1). The reaction dynamics were also compared with the isoelectronic reaction of the cyano radical (CN; X(2)Σ(+)) with acetylene (C(2)H(2); X(1)Σ(g)(+)) studied earlier.     

Observation of the intermediate states in the (Xe-Cl2)*→ XeCl* (B,C) + Cl reaction

The Xe-Cl₂ van der Waals complex formed in a supersonic expansion is excited in a two-photon process. The XeCl(B,C) reaction spectra (excitation of the complex and detection of the XeCl (B→X) and (C→A) fluorescence) are obtained in the region 290–310 nm. In addition to a diffuse band also obtained in the C action spectrum, the B action spectrum presents a vibronic structure similar to the Xe-Cl (B←X) absorption band. Xe-Cl₂ (¹Π_u) resonantly enhanced two-photon process with two chromophores is proposed to account for the results.     

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.     

Reaction of β-nitrostyrenes with benzene catalyzed by trifluoromethanesulfonic acid. Formation and reaction of n,n-dihydroxyiminium-benzyl dications

β-Nitrostyrenes are diprotonated on the nitro group to yield N,N-dihydroxyiminium-benzyl dications in trifluoromethanesulfonic acid. These dications comprise a new class of reagents that can react with benzene. The reaction is dependent on the substituent (H or alkyl group) at the β-position of nitrostyrene: β-nitrostyrene yields diphenylacetophenoneoxime, and β-methyl-β-nitrostyrene yields acetophenoneoxime and triphenylmethane. An essentially common mechanism is suggested to be involved in both reactions. These reactions are novel examples of acidcatalyzed reactions of nitro olefins.     

Reaction of CN(X2Σ+) with OCS and formation of SCN

The reaction between CN(X²Σ⁺) and OCS has been investigated using both time-resolved spectrophotometry and flash spectroscopy. The reaction is shown to be fast (k ⩾ 3 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹) and to lead to the formation of SCN.     

Investigation on the electronically excited state properties of multiwalled carbon nanotube (MDDA) in solution

Since their discovery by Iijima in 1991, carbon nanotubes have inspired considerable research inter-ests worldwide because of their unique structure to-gether with electric, magnetic, thermal conductivity and mechanical properties[1]. Apart from the hexag…     

The reaction of β-lactam carbenes with 3,6-di(2-pyrimidinyl)tetrazine: regulating products by reaction conditions

The reaction of β-lactam carbenes with 3,6-di(2-pyrimidinyl)tetrazine was studied, which produced good yields of novel 5-(3-[1,2,3]triazolo[1,5-a]pyrimidinyl)pyrrol-2-ones or pyrrolo[3′,2′:3,4]pyrrolo[1,2-a]pyrimidin-2-ones under heating at 100 °C or 140 °C, respectively. This work provided a highly efficient strategy for the construction of both [1,2,3]triazolo[1,5-a]pyrimidine and pyrrolo[3′,2′:3,4]pyrrolo[1,2-a]pyrimidine ring systems from the same reactants, and extended the application of β-lactam carbenes in the syntheses of complex heterocycles.     

Formation of thiazol-2(3H)-imines by reaction of α-amino acids,aroylisothiocyanates, and α-bromoketones in an ionic liquid

An efficient one-pot synthesis of functionalized thiazol-2(3H)-imines by a three-component reaction between aroylisothiocyanates, a-amino acids, and a-bromoketones in an ionic liquid is described.     

One-pot synthesis of α-phenylsulfinyl ketones by reaction of phenyl benzenethiosulfinate with enolate anions,and synthesis of sulfoxides and sulfides by its reaction with Grignard reagents

Phenyl benzenethiosulfinate reacts with enolate anions derived from ketones to give α-phenylsulfinyl ketones directly, together with minor amounts of α-phenylsulfanyl ketones. These are easily separated by forming the water-soluble sodium salts of the sulfinyl compounds. Grignard reagents also react with phenyl benzenethiosulfinate, to give mixtures of sulfoxides and sulfides.     

Formation of n-α-diazoacetylureas by the reaction of derivatives of 5-hydroxy-1,2,3-triazole-4-carboxamide with phenylisocyanate and phenyl isothiocyanate

The reaction of derivatives of 5-hydroxy-1,2,3-triazole-4-carboxamide with phenyl isocyanate and phenyl isothiocyanate proceeds at the 4-carboxamide fragment of the first, leading to the formation of derivatives of N-phenyl-N-(2-diazo-2-carbamoylacetyl)urea and -thiourea correspondingly.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1347–1350, October, 1992.     

Reactive quenching of OH A (2)Σ(+) by O(2) and CO: Experimental and nonadiabatic theoretical studies of H- and O-atom product channels

The outcomes following collisional quenching of electronically excited OH A (2)Σ(+) by O(2) and CO are examined in a combined experimental and theoretical study. The atomic products from reactive quenching are probed using two-photon laser-induced fluorescence to obtain H-atom Doppler profiles, O ((3)P(J)) atom fine structure distributions, and the relative yields of these products with H(2), O(2), and CO collision partners. The corresponding H-atom translational energy distributions are extracted for the H + O(3) and H + CO(2) product channels, in the latter case revealing that most of the available energy is funneled into internal excitation of CO(2). The experimental product branching ratios show that the O-atom producing pathways are the dominant outcomes of quenching: the OH A (2)Σ(+) + O(2) → O + HO(2) channel accounts for 48(3)% of products and the OH A (2)Σ(+) + CO → O + HCO channel yields 76(5)% of products. In addition, quenching of OH A (2)Σ(+) by O(2) generates H + O(3) products [12(3)%] and returns OH to its ground X (2)Π electronic state [40(1)%; L. P. Dempsey, T. D. Sechler, C. Murray, and M. I. Lester, J. Phys. Chem. A 113, 6851 (2009)]. Quenching of OH A (2)Σ(+) by CO also yields H + CO(2) reaction products [26(5)%]; however, OH X (2)Π (v(") = 0,1) products from nonreactive quenching are not observed. Theoretical studies characterize the properties of energy minimized conical intersections in four regions of strong nonadiabatic coupling accessible from the OH A (2)Σ(+) + CO asymptote. Three of these regions have the O-side of OH pointing toward CO, which lead to atomic H and vibrationally excited CO(2) products and∕or nonreactive quenching. In the fourth region, energy minimized points are located on a seam of conical intersection from the OH A (2)Σ(+) + CO asymptote to an energy minimized crossing with an extended OH bond length and the H-side of OH pointing toward CO in a bent configuration. This region, exoergic with respect to the reaction asymptote, is likely to be the origin of the dominant O + HCO product channel.     

Global potential energy surface, vibrational spectrum, and reaction dynamics of the first excited (Ã (2)A(')) state of HO(2)

The authors report extensive high-level ab initio studies of the first excited (A??(2)A(')) state of HO(2). A global potential energy surface (PES) was developed by spline-fitting 17?000 ab initio points at the internal contracted multireference configuration interaction (icMRCI) level with the AVQZ basis set. To ascertain the spectroscopic accuracy of the PES, the near-equilibrium region of the molecule was also investigated using three interpolating moving least-squares-based PESs employing dynamically weighted icMRCI methods in the complete basis set limit. Vibrational energy levels on all four surfaces agree well with each other and a new assignment of some vibrational features is proposed. In addition, the dynamics of both the forward and reverse directions of the H+O(2)(a??(1)Δ(g))?OH+O reaction (J=0) were studied using an exact wave packet method. The reactions are found to be dominated by sharp resonances.     

A one-pot reaction of (chlorocarbonyl) phenyl ketene with β-ketoamides and thiochromen-2-one

Readily available (chlorocarbonyl)phenyl ketene and a varied set of β-ketoamides were reacted in a one-step procedure to produce 2-pyrone derivatives. β-Ketoamide derivatives are versatile intermediates for the synthesis of heterocyclic compounds. For instance, 1-morpholino-3-phenyl-1,3-propanedione, 1-phenyl-3-piperidino-1,3-propanedione, 1-phenyl-3-pyrrolidino-1,3-propanedione, 1-piperidino-1,3-butanedione, 1-morpholino-2-phenyl ethanone were used in these reactions to produce 2-pyrone derivatives. In addition, the preparation of 4-hydroxy-3-phenylthiochromeno[4,3-b]pyran-2,5-dione derivatives and 4-hydroxy-7-methyl-3-phenyl pyrano[3,2-c]chromeno-2,5-dione were described. For the synthesis of these compounds 4-hydroxy-2H-thiochromen-2-ones and 4-hydroxy-8-methyl-2H-chromen-2-one were reacted with (chlorocarbonyl)phenyl ketene and the final products were isolated in good yields.     

Synthesis of 2-arylpyrrolidines by reaction of γ-ureidoacetals with benzene-1,3,5-triol

New 2,2′-(2,4,6-trihydroxybenzene-1,3-diyl)dipyrrolidine derivatives have been synthesized by reaction of benzene-1,3,5-triol (phloroglucinol) with γ-ureidoacetals in the presence of trifluoroacetic acid as catalyst.     

Formation of “three-bridge” cobalt-copper commo-cluster with the (B-H)3...Cu bond in the reaction of [Cs][commo-3,3′-Co(1,2-C2B9H11)2] with copper(i) and copper(ii) compounds

Zwitterionic 4,8,8′-exo-{Ph₃PCu}-4,8,8′-(μ-H)₃-commo-3,3′-Co(1,2-C₂B₉H₉)-(1′,2′-C₂B₉H₁₀) and ionic [(PPh₃)₃Cu][commo-3,3′-Co(1,2-C₂B₉H₁₁)₂ complexes were synthesized in moderate yields by the reaction of anionic commo-complex [Cs][commo-3,3′-Co-(1,2-C₂B₉H₁₁)₂]) in a CH₂Cl₂ solution with anhydrous CuCl₂ or CuCl in the presence of PPh₃. The complexes were also synthesized by alternative methods and characterized by NMR and X-ray diffraction methods.