N-H and N-C Bond Dissociation Pathways in Ultraviolet Photodissociation of Dimethylamine.

We investigated the interlinked N-H and N-C photochemistry of primary and secondary amines via the state-resolved detection of vibrationally excited CH product and H atom product by 200-235 nm dimethylamine photodissociation using resonance-enhanced multiphoton ionization (REMPI) and velocity map imaging (VMI) techniques. The out-of-plane bending (ν) vibrationally excited CH showed a bimodal translational energy distribution that became unimodal with a near-zero product yield at longer photolysis wavelengths (λ). In contrast, a unimodal distribution was observed for the C-H stretching (ν) vibrationally excited CH products with an almost constant product yield in the examined λ region.

Primary and Secondary Processes in the Ultraviolet Photodissociation of CpCo(CO) (Cyclopentadienylcobalt Dicarbonyl).

We investigated the photodissociation dynamics of CpCo(CO) (cyclopentadienylcobalt dicarbonyl) in metal-to-ligand charge transfer (MLCT) bands. By employing DFT calculations, the absorption band (210-240 nm) was characterized as a charge transfer from the Co center to the Cp (cyclopentadienyl, CH) ligand. Ion imaging was utilized to analyze the CO fragments and coordinatively unsaturated complexes (CpCoCO, CpCo, and CoCH) across the entire MLCT band.

Nascent Vibrational Energy Distribution of CS(XΣ) Generated in the S(D) + CS Reaction.

The internal energy distributions of reaction products are important information in clarifying the mechanism of chemical reactions. There are few reports of the nascent vibrational energy distribution of CS(XΣ) generated in the S(D) + CS reaction. As long as S(D) is produced by photodissociation of CS, CS(XΣ), as a product of the chemical reaction and as a photoproduct of CS is indistinguishable.

Generation of Highly Vibrationally Excited CO in Sequential Photodissociation of Iron Carbonyl Complexes.

Ultraviolet photochemistry of iron pentacarbonyl, Fe(CO), was investigated with resonantly enhanced multiphoton ionization (REMPI) spectroscopy and ion imaging. The REMPI spectrum of CO photofragments, generated by ultraviolet irradiation of Fe(CO), showed the generation in the highly vibrationally excited states with = 11-15. Analysis of the band intensities observed in the 213-235 nm region indicated that the high- CO generation was maximized at around 220 nm.

Primary and Secondary Loss of CO and NO Ligands in the Ultraviolet Photodissociation of the Heteroleptic Co(CO)NO Complex.

The photodissociation dynamics of the heteroleptic Co(CO)NO complex were investigated in the metal-to-carbonyl (CO) ligand charge-transfer band to compare the reactivity of the CO and nitrosyl (NO) ligands. The final state distributions of both the CO and NO fragments were measured using resonance-enhanced multiphoton ionization (REMPI) spectroscopy and velocity-map ion-imaging. The primary CO photofragment was differentiated from the secondary fragments of the subsequent unimolecular decomposition of coordinatively unsaturated intermediates by comparing the momentum distributions.

Direct Detection of S(P) and S(D) Generated in the O(D) + OCS Reaction: Mechanism of the Formation of S(XΣ and aΔ).

Highly vibrationally excited disulfur S in the XΣ and aΔ states has been detected in the gaseous mixture of O and OCS irradiated with light at 266 nm. Generation of CO in the reaction system has been reported; however, no direct detection of sulfur atoms (S(P) and S(D)) has been made. In the present study, we have employed the two-photon laser-induced fluorescence (2P-LIF) technique to detect S(P) and S(D) directly and recorded the time profiles of the atoms at varying pressures of OCS.

Detection of the Excited-State NH (Ã A) in the Ultraviolet Photodissociation of Methylamine.

Ion-imaging and dispersed fluorescence spectroscopy are employed for the photodissociation dynamics study of methylamine in the photolysis wavelength range 205-213 nm. The methyl radical product is found to populate a wide range of ro-vibrational states, among which the CH fragment generated in the v = 0 state shows a bimodal kinetic energy distribution. The internal energy analysis of the NH counterproduct indicates that a lower kinetic energy component, which was observed only with the CH(v=0) fragment, energetically matches the electronically excited ÃA state.

Impact of Diradical Spin State (Singlet vs Triplet) and Structure (Puckered vs Planar) on the Photodenitrogenation Stereoselectivity of 2,3-Diazabicyclo[2.2.1]heptanes.

Versatile transformations of azo compounds are utilized not only in synthetic organic chemistry but also in materials science. In this study, a hitherto unknown stereoselectivity was observed by low-temperature in situ NMR spectroscopy for the photochemical denitrogenation of a cyclic azoalkane (2,3-diazabicyclo[2.2.

Multiple product pathways in photodissociation of nitromethane at 213 nm.

In this paper, we present a photodissociation dynamics study of nitromethane at 213 nm in the π → π(*) transition. Resonantly enhanced multiphoton ionization spectroscopy and ion-imaging were applied to measure the internal state distributions and state-resolved scattering distributions of the CH3, NO(X (2)Π, A (2)Σ(+)), and O((3)PJ) photofragments. The rotationally state-resolved scattering distribution of the CH3 fragment showed two velocity components, of which the slower one decreased the relative intensity as the rotational and vibrational excitations.

Photodissociation dynamics of C₃H₅I in the near-ultraviolet region.

The ultraviolet photodissociation dynamics of allyl iodide (C3H5I) have been studied by ion-imaging at 266 nm and 213 nm. These photolysis wavelengths are located in the two lowest absorption bands in the near-ultraviolet region. The atomic iodine products were detected by [2+1] resonantly enhanced multiphoton ionization spectroscopy.

Kinetics and dynamics on the formation of S2(X3Σg–,a1Δg) in the S(1D) + OCS reaction.

The reaction of electronically excited sulfur S((1)D) with OCS has exothermic channels generating S(2) in two electronic states X(3)Σ(g)– and a(1)Δ(g). The a(1)Δ(g) state is correlated directly to the reactants via the spin-allowed singlet surface; the X(3)Σ(g)– state, on the other hand, is a product of the spin-forbidden channel. There has been no report on kinetic evidence for the simultaneous generation of the two electronic states, although the two electronic states have been detected so far.

Rate coefficients for vibrational relaxation of OH(X2Π, v = 1-4) by He.

The vibrational relaxation of OH(X(2)Π) by collisions with rare gases is very slow due to small molecular interactions. No measurement of the rate coefficients has been made for relaxation of relatively low vibrational levels v ≤ 4 of OH by He, and there is only one report of the upper limit for v = 2, <1 × 10(-14) cm(3) molecule(-1) s(-1). In this article, we have studied vibrational relaxation of the levels v = 1-4 of OH(X(2)Π) by collisions with He.

Vibrational relaxation of O2(X3Σ(-)g, v = 6-8) by collisions with O2(X3Σ(-)g, v = 0): solution of the problems in the integrated profiles method.

The linear kinetic analysis called the integrated profiles method (IPM) makes it simple to analyze the multistep relaxation processes of vibrational manifold. The problem that plots for linear regression in the IPM analysis cannot be made, however, has been found in the study of self relaxation of O2(X3Σ(-)g, v = 6-8). The cause of the problem is the identical time-dependence of the populations of the adjacent vibrational levels.

Theoretical molecular double-core-hole spectroscopy of nucleobases.

Double-core-hole (DCH) spectra have been investigated for pyrimidine, purine, the RNA/DNA nucleobases, and formamide, using the density functional theory (DFT) method. DCH spectra of formamide were also examined by the complete-active-space self-consistent-field (CASSCF) method. All possible single- and two-site DCH (ssDCH and tsDCH) states of the nucleobases were calculated.

Acceleration of the reaction OH + CO → H + CO2 by vibrational excitation of OH.

The collision complex formed from a vibrationally excited reactant undergoes redissociation to the reactant, intramolecular vibrational relaxation (randomization of vibrational energy), or chemical reaction to the products. If attractive interaction between the reactants is large, efficient vibrational relaxation in the complex prevents redissociation to the reactants with the initial vibrational energy, and the complex decomposes to the reactants with low vibrational energy or converts to the products. In this paper, we have studied the branching ratios between the intramolecular vibrational relaxation and chemical reaction of an adduct HO(v)-CO formed from OH(X(2)Π(i)) in different vibrational levels v = 0-4 and CO.

Nascent vibrational energy distributions of O2(X3Sigma(g)-, nu = 6-13) generated in the photolysis of O3 at 266 nm.

The vibrational levels of O2(X3Sigma(g)-) generated in the ultraviolet photolysis of O3 at 266 nm were detected via laser-induced fluorescence (LIF) of the B3Sigma(u)- - X3Sigma(g)- system. The nascent vibrational energy distributions of O2(X3Sigma(g)-, nu = 6-13) have been measured by two different methods. One is a kinetic analysis based on the originally developed integrated profiles method (IPM).

The origin of the generalized anomeric effect: possibility of CH/n and CH/pi hydrogen bonds.

Ab initio MO calculations were carried out at the MP4/6-311++G(3df,3pd)//MP2/6-311++G(3df,3pd) level to investigate the conformational Gibbs energy of a series of methyl ethers CH(3)O-CH(2)-X (X=OH, OCH(3), F, Cl, Br, CN, C triple bond CH, C(6)H(5), CHO). It was found that the Gibbs energy of the gauche conformers is lower in every case than that of the corresponding anti conformers. In the more stable gauche conformers, the interatomic distance between X and the hydrogen atom was shorter than the sum of the van der Waals radii.

Molecular dynamics studies of the structural change in 1,3-diamino-2,4,6-trinitrobenzene (DATB) in the crystalline state under high pressure.

Molecular dynamics (MD) calculations were performed to reveal the effect of high pressure on the crystal of 1,3-diamino-2,4,6-trinitrobenzene (DATB). The coordinates of the individual atoms in the DATB crystal structure were obtained using X-ray diffraction analysis. The primary simulation cell consists of 54 molecules in a monoclinic cell, corresponding to 27 unit cells obtained by replicating the experimentally determined unit cell.

Kinetic study of vibrational energy transfer from a wide range of vibrational levels of O2(X(3)Sigma(g)-, v = 6-12) to CF4.

A wide range of vibrational levels of O2(X(3)Sigma(g)(-), v = 6-13) generated in the ultraviolet photolysis of O3 was selectively detected by the laser-induced fluorescence (LIF) technique. The time-resolved LIF-excited B(3)Sigma(u)(-)-X(3)Sigma(g)(-) system in the presence of CF4 has been recorded and analyzed by the integrated profiles method (IPM). The IPM permitted us to determine the rate coefficients k(v)(CF4) for vibrational relaxation of O2(X(3)Sigma(g)(-), v = 6-12) by collisions with CF4.

Vibrational relaxation of O2(X3 Sigma g-, v = 9-13) by collisions with O2.

Vibrationally excited O(2)(X(3) Sigmag(-)) was generated in the UV laser flash photolysis of O(3) and single vibrational level was detected via laser-induced fluorescence (LIF) in the B(3) Sigmau(-)-X(3) Sigmag(-) system. The time-resolved LIF of adjacent vibrational levels has been analyzed by the integrated-profiles method and the rate coefficients for single-quantum relaxation, O(2)(X(3)Sigmag(-), v = 9-13)+ O(2)(v = 0)--> O(2)(X(3)Sigmag(-), v - 1)+ O(2)(v = 1), have been determined. To the best of our knowledge, the rate coefficients for v = 12 and 13 are measured for the first time in the present study.

Origin of the pi-facial stereoselectivity in the addition of nucleophilic reagents to chiral aliphatic ketones as evidenced by high-level ab initio molecular-orbital calculations.

Ab initio molecular-orbital (MO) calculations were carried out, at the MP2/6-311++G(d,p)//MP2/6-31G(d) level, to investigate the conformational Gibbs energy of alkyl 1-cyclohexylethyl ketones, cyclo-C6H11CHCH3-CO-R (R = Me, Et, iPr, and tBu). In each case, one of the equatorial conformations was shown to be the most stable. Conformers with the axial CHCH3COR group were also shown to be present in an appreciable concentration.

The anomeric effect revisited. A possible role of the CH/n hydrogen bond.

Ab initio MO calculations were carried out at the MP2/6-311++G(d,p) level to investigate the conformational energy of 2-substituted oxanes and 1,3-dioxanes. It has been found that the Gibbs free energies of the axial conformers are smaller than those of the corresponding equatorial conformers in every case when the 2-substituent Z is electron withdrawing (OCH(3), F, Cl, Br). The difference in Gibbs energy between the equatorial and axial conformers DeltaG(eq-ax) increases from Z=OCH(3) to F, Cl, and then to Br.

Quenching and vibrational relaxation of SO(B3Sigma-, v'

Fluorescence from a single vibronic level of SO(B3Sigma-, v' View Article and Find Full Text PDF

Efficient vibrational relaxation of O2(X 3sigma(g)-, nu = 8) by collisions with CF4.

A laser flash photolysis-laser-induced fluorescence (LIF) technique has been employed to study the relaxation kinetics of vibrationally excited O2(X 3sigma(g)-. The time-resolved LIF excited B 3sigma(u)(-)-X 3sigma(g)- system has been recorded and analyzed by the integrated-profiles method. The rate coefficient for vibrational relaxation of O2(X 3sigma(g)-, nu = 8) by collisions with CF(4), [1.

Isotope effects in the dissociation of the B 1A1 state of SiH2, SiHD, and SiD2 using three-dimensional wave packet propagation.

Dissociations after the A 1B1-->B 1A1 photoexcitation of SiH2, SiHD, and SiD2 were studied to investigate excited-state dynamics and effects of the initial vibrational state. The cross section (sigma) for the photodissociation relative to SiH2(B)-->Si(1D)+H2 and the rovibrational population of the H2 fragment were computed using the wave packet propagation technique based on the three-dimensional potential energy surfaces (PESs) of the A and B electronic states and the transition dipole surfaces, which were reported in our previous paper [J. Chem.