T. Hikida

Fluorescence of excited ethynyl radicals produced by pulsed vacuum ultraviolet photolyses of C2H2, C2D2, and C2HBr

Electronically excited ethynyl radicals were produced by pulsed vacuum ultraviolet photolyses of C2H2, C2D2, and C2HBr. The broad fluorescence spectra of the ethynyl radical extending from 410 to wavelengths longer than 750 nm were found to be insensitive to parent molecules photolyzed, their pressures, and also pressures of an added gas, He. Time profiles of the fluorescence intensity were found to be a superposition of two components. The dominant component is due to excited ethynyl radicals formed within the excitation pulse duration of ∼20 ns. At higher pressures, however, some minor contribution from a long‐lived precursor to the fluorescence was detected. Zero‐pressure decay rates and quenching rate constants were obtained. Formation mechanism of fluorescent ethynyl radicals is discussed briefly.

Lifetime studies of NO(A 2Σ+, υ′ = 4), NO(B 2Π, υ′ = 9) and NO(D2 Σ+, υ′ = 0)

Abstract Lifetimes of NO(A 2 Σ + , υ′=4), NO(B 2 Π, υ′ = 9) and NO(D 2 Σ + , υ = 0) have been studied using a single photon counting techniques combined with nanosecond flash excitation. The zero-pressure lifetimes and quenching rate constants have been obtained. These values and our earlier reports show that both NO(B 2 Π, υ′ = 9) and NO(C 2 Σ, υ′ = 0) predissociate with large quantum yields of 0.9 or more. On the contrary, NO(A 2 Σ + , υ′ = 4) and NO(D 2 Σ + , υ′ = 0) undergo very slow predissociation, though these levels are more energetic than NO(C 2 Π, υ′ = 0). Possible dissociation mechanisms are discussed.

Lifetime of NO C2Π(υ′ = 0)

Abstract The lifetime of NO C 2 Π(υ′ = 0) was measured by a single photon counting technique using a nanosecond light pulser. After deconvolution, the decay rate constant of the predissociating rotational levels, (0,7 ± 0.1) x 10 9 s −1 , and that of the non-predissociating rotational levels, (7.2 ± 2.0) x 10 7 s −1 , were obtained. The self-quenchin rate constant for the non-predissociating levels of NO C 2 Π(υ′ = 0) was found to be 4.5 x 10 11 M −1 s −1 .

Mercury-photosensitized luminescence of NH3 at low pressure

Abstract The mercury-photosensitized luminescence of ammonia was investigated at low pressures. With [NH 3 ] 3 ] 3 P 0 ) by using well established reaction rate constants. The origin of a new emitter is discussed briefly and although it is not certain, an encounter complex formed between an Hg(6 3 P 1 ) atom and an ammonia molecule may be responsible.

Fluorescence of nitric oxide excited by the 184.9 nm mercury resonance line

The fluorescence of NO was obtained by excitation from the 184.9 nm resonance line of a low pressure mercury lamp. It was found that the β (v′=9) emission was induced by the absorption of the 184.9 nm line for [NO]=1.0 torr. Quenching of the β (v′=9) bands by He or N2 molecules was accompanied by an enhancement of the γ bands, v′=4 or 0 and 1, respectively. When CO was added to NO, intensities of the emission were weakened. These effects were explained by the following reaction scheme.

TICT state formation in the 4′-dimethylaminoacetophenone–α-cyclodexdtrin inclusion complex

Abstract Fluorescence properties of excited 4′-dimethylaminoacetophenone (DMAAP) complexed with α-cyclodextrin (CD) were studied. The complex exhibited dual fluorescence in neutral aqueous solutions and no TICT fluorescence was observed in alkaline solutions. The dependence of TICT emission intensity on pH and α-CD concentration suggested that a 1:2 DMAAP–α-CD complex, which was formed by the association of the 1:1 complex and α-CD, was responsible for the TICT fluorescence.

Formation of NH(c1Π), NH(A 3Π) and NCO(A 2Σ) in the VUV photolysis of HNCO

Abstract Photodissociative excitation processes of gaseous HNCO are studied in the wavelength region 107–180 nm using synchrotron radiation as a light source. Fluorescence excitation spectra of the photofragments, NH(c 1 Π, A 3 Π) and NCO(A 2 Σ), are measured under near collision-free conditions. The quantum yields for formation of these excited radicals are also determined.

Fluorescence lifetime studies of no a 2Σ+(ν = 5, N = 9), B2Π32(ν = 8, J = 8.5), CwΠ32(ν = 1, J = 8.5), D2Σ+ (ν = 0, N = 5) and D2Σ+(ν = 1, N = 9)

Abstract Fluorescence decay profiles of NO excited levels slightly above the dissociation limit have been measured by a single-photon counting technique with nanosecond pulse excitation using an iodine flash lamp. Three iodine atomic lines in the vicinity of 180 nm are found to bring NO molecules into the levels A2Σ+(ν = 5, N = 9), B22Π 3 2 (ν = 8, J = 8.5), C2Π 3 2 (ν = 1, J = 8.5), D2Σ+(ν = 0, N = 5) and D2Σ+(ν = 1, N = 9). Extrapolated zero-pressure lifetimes for single rotational levels are obtained, except for the C state where only a lifetime of ⩽0.4 ns was obtained. Self-quenching rate constants are also determined under higher-pressure conditions. Helium was found to quench the NO A2Σ+(ν′ = 5) fluorescence very efficiently.

Two-dimensional photoelectron spectroscopy of acetylene: Rydberg-valence interaction between the (3σg)−1(3pσu)1 and (3σg)−1(3σu)1 states

Two-dimensional photoelectron spectroscopy is performed for studying autoionization of acetylene in the Franck–Condon gap between the X 2Πu and A 2Ag states of C2H2+. The photoelectron spectrum in the photon energy range from 12.8 to 13.6 eV shows exclusive vibrational excitation of the symmetric C–H stretching mode ν1 of C2H2+(X 2Πu), which results from autoionization of the valence state (3σg)−1(3σu)1. Vibrational frequencies with anharmonicities of the ν1 and ν2 (the symmetric C–C stretch) modes are determined by a least-squares fit of the ionization energies of the observed peaks to a second order expansion. At the photon energy of 14.120 eV, autoionization of the Rydberg state (3σg)−1(3pπu)1 leads to a complicated photoelectron spectrum where probably the trans-bending mode ν4 of C2H2+(X 2Πu) as well as ν1 is excited, reflecting a substantial geometrical change during autoionization. Furthermore, a similar excitation of the ν4 mode is observed at ∼13.8 eV. An excellent agreement in positions of the v...

Superexcited states of OCS probed by using photoelectron spectroscopy for autoionizing atomic sulfur

Neutral dissociation of superexcited states of OCS has been studied by two-dimensional photoelectron spectroscopy using synchrotron radiation in the photon energy range of 14.2–16.8 eV. A two-dimensional spectrum exhibits noticeable features which are assigned as resulting from autoionizing transitions of excited atomic sulfur, S*, from Rydberg states converging to S+(2Do) to S+(4So). The precursor molecular states leading to S*+CO are considered to be multiple-electron-excited Rydberg states, OCS*(Dis), converging to OCS+ with 2Σ− and/or 2Δ symmetry. The electron signal counts due to autoionization of S* show enhancement at excitation photon energies for the Rydberg states, OCS*(RB), converging to OCS+(B 2Σ+). These results support a predissociation mechanism for the formation of S*: conversion from OCS*(RB) to OCS*(Dis). The quantum yield for the predissociation is evaluated to be ∼1% at the photon energy corresponding to the 5sσ state of OCS*(RB).