Yukio Nakano

UV emission of I2 from the ion-pair state following amplified spontaneous emission

This paper reports the results of processes resulting in D0(u) (+)-X (1)Sigma(g) (+) emission when a single rovibrational level of the E0(g) (+) state is prepared. Our study reveals that two kinds of processes populate the D0(u) (+) state; which one occurs depends on the experimental conditions. One process involves amplified spontaneous emission from the E0(g) (+) state. The other is collision-induced energy transfer in self-quenching. We distinguish these two processes from the time profiles of fluorescence signals. These processes give completely different vibrational distributions in the D0(u) (+) state from a given rovibrational level of the E0(g) (+) state. The discrepancy between our results and previous results for the E0(g) (+)-->D0(u) (+) relaxation is briefly discussed.

Kinetics and mechanism of the gas phase reaction of Cl atoms and OH radicals with bromobenzene

Abstract Relative rate techniques were used to study the kinetics and mechanism of the reaction of Cl atoms and OH radicals with bromobenzene (C 6 H 5 Br) in 20–700 Torr of N 2 , O 2 , or air diluent at 295±2 K. Using the observed rate constant ratios k (C 6 H 5 Br+Cl)/ k (C 2 H 5 Cl+Cl)=1.56±0.05 and k (C 6 H 5 Br+Cl)/ k (C 2 H 6 +Cl)=0.24±0.01, the C 6 H 5 Br+Cl rate constant is determined to be k( C 6 H 5 Br + Cl )=(1.32±0.20)×10 −11 cm 3 molecule −1 s −1 giving exclusively C 6 H 5 Cl through a displacement mechanism. Using the observed rate constant ratios k (C 6 H 5 Br+OH)/ k (C 6 H 6 +OH)=0.77±0.06 and k (C 6 H 5 Br+OH)/ k (C 2 H 4 +OH)=0.11±0.004, the C 6 H 5 Br+OH rate constant is determined to be k( C 6 H 5 Br + OH )=(9.37±2.04)×10 −13 cm 3 molecule −1 s −1 . The product expected from a displacement mechanism, phenol, was not observed (

Excited state dynamics of Cl2O in the near ultraviolet

The state-resolved and isotope-specific detection of nascent ClO generated from the photodissociation of Cl2O parent molecules is performed by observing single-color (2+1) resonance enhanced multiphoton ionization (REMPI) spectra following excitation in the wavelength range from 336 to 344 nm; additionally state-resolved detection of nascent ClO is performed by observing single-color two photon laser-induced fluorescence. The REMPI spectrum is assigned to the ClO(C 2Σ−,v′=0←X 2ΠΩ,v=0) transition. The population of rotational states up to J=130 is evidence of large rotational excitation induced by a strong dependence of the excited potential energy surface (PES) on the Jacobi angle γ. Formation of the 2Π3/2 spin-orbit state is preferred: P(2Π1/2):P(2Π3/2)=0.30±0.05 suggesting significant radiationless transfer from the excited PES to closely lying neighboring states. The anisotropy parameter for the transition is determined to be β=0.35 independent of the ClO quantum state. The principal excited electronic...

Electronic structure and photochemical reaction intermediates of octakis(1,1,2-trimethylpropyl)octasilacubane

Abstract The electronic spectrum and photochemical reaction intermediates of octakis(1,1,2-trimethylpropyl)octasilacubane have been studied by analyzing the UV-VIS spectrum and transient absorption spectra. The first three absorption bands of the UV-VIS spectrum have been assigned to the transitions from HOMO (t 1u symmetry) to LUMO (a 2u ), from HOMO-1 (t 1g ) to LUMO, and from HOMO to LUMO+1 (t 2g ) by making reference to the results obtained by INDO/S-CI calculations. The photochemical reaction intermediate has been elucidated to be the isomer whose decay rate constant is 57±3 s −1 . The quenching rate constant of the isomer by oxygen is ca. 3×10 5 M −1 s −1 .

Infrared radiative decay dynamics from the γ 1u (3P2), H 1u (3P1), and 1u (1D2) ion-pair states of I2 observed by a perturbation facilitated optical-optical double resonance technique

We report the spectroscopic and temporal analyses on the amplified spontaneous emission (ASE) from the single rovibrational levels of the Ω = 1u ion-pair series, γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2), of I2 by using a perturbation facilitated optical-optical double resonance technique through the c (1)Πg ∼ B (3)Π(0u (+)) hyperfine mixed valence state as the intermediate state. The ASE detected in the infrared region was assigned to the parallel transitions from the Ω = 1u ion-pair states down to the nearby Ω = 1g ion-pair states. The subsequent ultraviolet (UV) fluorescence from the Ω = 1g states was also observed and the relative vibrational populations in the Ω = 1g states were derived through the Franck-Condon simulation of the intensity pattern of the vibrational progression. In the temporal profiles of the UV fluorescence, an obvious delay in the onset of the fluorescence was recognized after the excitation laser pulse. These results revealed that ASE is a dominant energy relaxation process between the Ω = 1u and 1g ion-pair states of I2. Finally, the lifetimes of the relevant ion-pair states were evaluated by temporal analyses of the UV fluorescence. The propensity was found which was the longer lifetime in the upper level of the ASE transitions tends to give intense ASE.