Display omitted
•The state-resolved scattering distributions of NO loss of Co(CO)3NO are measured by ion-imaging.•The fast and slow NO photofragments are observed, indicating two production origins ...in NO loss.•The fast NO fragments observed in certain final states show anisotropic angular distributions.•The NO fragment orientations are ascribed to transient bent structure in the photoexcited state.
Ultraviolet photodissociation dynamics of tricarbonylnitrosylcobalt, Co(CO)3NO, is studied by ion-imaging. The photon energy is large enough to eliminate both NO and CO ligands in this heteroleptic complex, among which state-specific scattering is observed in the NO loss channel. The velocity distributions of the NO ligands exhibit clear evidence of two pathways. NO fragments with higher and lower kinetic energies are ascribed to direct dissociation in the electronic excited state and secondary decomposition following relaxation processes, respectively. The state-specific angular distribution of the faster component corroborates the rotational alignment, indicating the bent coordination of the nitrosyl ligand in the photoexcited state.
Ab initio MO calculations were carried out to investigate the conformational preference of
n-propyl halides, isobutyl halides,
sec-butyl halides, and
n-butyl halides. It has been found in most cases ...that the conformer in which a methyl group is close to the halogen atom is favored.
Ab initio MO calculations were carried out to investigate the conformational preference of
n-propyl halides, isobutyl halides,
sec-butyl halides, and
n-butyl halides. It has been found in most cases that the conformer in which a methyl group is close to the halogen atom is favored. The distance between the halogen atom and one of the hydrogens in the interacting CH
3 group has been shown, in every case, to be shorter than the van der Waals distance. Natural bond orbital (NBO) charges have given results consistent with this finding. We suggest that the CH/
n hydrogen bond contributes in determining the conformation of these molecules.
Display omitted
•Oxygen atoms were detected by vacuum UV emission after two-photon excitation.•Time-resolved vacuum UV emission was recorded at varying pressures of He and N2.•The kinetic analysis of ...the time profiles was made by the integrated profiles method.•The quenching rate coefficients of O(3p 3P) by He and N2 have been determined.•State-to-state (3p 3P → 3 s 3S) quenching rate coefficients have been determined.
Electronically excited atomic oxygen O(2p33p3PJ) was prepared by ultraviolet (225.6 nm) two-photon excitation from the ground state 2p43P2. The 2p33p3PJ state transfers to the 2p33s3S state via the infrared transition at 845 nm and/or by collisions with ambient gases. The vacuum ultraviolet (VUV) emission at 130 nm via the transition 2p33s3S → 2p43PJ was detected, and the time-resolved VUV emission at varying pressures of He and N2 was recorded. The kinetic analysis made by the integrated profiles method has given the rate coefficients not only for the overall quenching of the 2p33p3PJ state but also for the state-to-state quenching 2p33p3PJ → 2p33s3S by He and N2.
Display omitted
•We investigate the photodissociation dynamics of methyl nitrite.•Moderate vibrational excitation and highly rotational excitation of NO are observed.•The rotational state ...distribution of NO is well represented by a Gaussian function.•The state-resolved scattering distributions of the NO product are measured.•The translational energy release is closely correlated to the NO rotational energy.
State-resolved scattering distributions of the NO product in the photodissociation of CH3ONO were measured at 213nm with resonantly-enhanced multiphoton ionization spectroscopy and ion-imaging. The spectra of the NO product displayed the vibrational population up to the v=3 state having the rotational state-distribution with a Gaussian-like function. The scattering data of the NO (v=1) product indicate that the rotational excitation of the NO fragment and the translational energy release are fairly well compensated. This result is explained as being an outcome of the strong repulsion in the CH3ONO bond in the S2 state.
Collision-free lifetimes and deactivation rate constants of SO(B3Σ-, v ‘ = 0, 1, and 2) by collisions with He have been determined. SO(X3Σ-) was generated in the photolysis of SO2 at 193 nm (ArF ...laser) and excited to a single rovibrational level of B3Σ- with a pulsed ultraviolet laser. We recorded dispersed fluorescence spectra, and found that 0−12 (350.8 nm), 1−14 (368.5 nm), and 2−17 (401.2 nm) bands are suitable for detecting fluorescence from single vibrational level of interest. Time profiles of wavelength-resolved fluorescence were recorded at various buffer gas pressures (5−165 Torr of He). Deconvolution by the integrated phase plane method derives apparent fluorescence lifetime at a given pressure. Total pressure dependence of fluorescence decay rates leads to collision-free lifetimes and rate constants for deactivation of SO(B3Σ-, v ‘ = 0, 1, and 2) by collisions with He. Lifetimes of SO(B3Σ-) have been determined to be (28 ± 2) ns (v ‘ = 0), (30 ± 3) ns (v ‘ = 1), and (27 ± 4) ns (v ‘ = 2). Rate coefficients for deactivation of SO(B3Σ-) by He have been obtained to be (6.3 ± 0.3) × 10-12, (3.9 ± 0.2) × 10-11, and (1.3 ± 0.2) × 10-10 in units of cm3 molecule-1 s-1 for v ‘ = 0, 1, and 2, respectively. To the best of our knowledge, deactivation rate constants for v ‘ = 0 and 1 of SO(B3Σ-) are measured for the first time in the present study. The large rate coefficient of deactivation by He and vibrational level dependence is explained by predissociation via the C3Π state.
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 Ã
A
state. The dispersed fluorescence spectrum, whose band structure is assigned to the Ã
A
→ X̃
B
transition, provides evidence of the CH
(v=0) + NH
(Ã
A
) pathway. The branching mechanism of the product pathway is discussed in terms of nuclear dynamics in the long-range region, where the conical intersection between the excited- and ground-state potential energy surfaces can play a significant role.
Theoretical Molecular Double-Core-Hole Spectroscopy of Nucleobases Takahashi, Osamu; Tashiro, Motomichi; Ehara, Masahiro ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
11/2011, Volume:
115, Issue:
44
Journal Article
Peer reviewed
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. The generalized relaxation energy and interatomic generalized relaxation energy were evaluated from the energy differences between ssDCH and single-core-hole (SCH) states and between tsDCH and SCH states, respectively. The generalized relaxation energy is correlated to natural bond orbital charge, whereas the interatomic generalized relaxation energy is correlated to the interatomic distance between the core holes at two sites. The present analysis using DCH spectroscopy demonstrates that the method is useful for the chemical analysis of large molecular systems.
Highly vibrationally excited disulfur S2 in the X3Σg – and a1Δg states has been detected in the gaseous mixture of O3 and OCS irradiated with light at 266 nm. Generation of CO2 in the reaction system ...has been reported; however, no direct detection of sulfur atoms (S(3P) and S(1D)) has been made. In the present study, we have employed the two-photon laser-induced fluorescence (2P-LIF) technique to detect S(3P) and S(1D) directly and recorded the time profiles of the atoms at varying pressures of OCS. Kinetic analyses of the profiles show that (i) S(1D) is generated in the O(1D) + OCS reaction and consumed by the S(1D) + OCS reaction, and (ii) S(3P) is mainly generated in the O(1D) + OCS reaction instead of quenching of S(1D) by collisions with OCS and ambient gases. The vibrational levels v = 19 and 10 of the respective electronic states X3Σg – and a1Δg of S2 were detected in the O3/OCS/266 nm system. The two vibrational levels cannot be generated by the available energy of the S(3P) + OCS reaction, giving evidence that S2 in the X3Σg – and a1Δg states are generated by the S(1D) + OCS reaction.
PDF