Search

Cavity ring-down spectroscopy (CRDS) is used to investigate the rate constants for the reaction of BrO with C[H.sub.3][O.sub.2] at atmospheric temperatures. The results have shown that the reaction of BrO with C[H.sub.3][O.sub.2] will affect the halogen chemistry in the troposphere, thus contributing to ozone destruction cycles.

A study of the reaction of nitrate radical with dimethyl sulfide using cavity ring-down spectroscopy in 20-200 Torr of [N.sub.2] diluent in the temperature range of 283-318 K is presented. The rate constant for the reaction was found to be temperature dependent and pressure independent.

Cavity ring-down spectroscopy is applied to a kinetic study of the reaction of NO3 with CH3I in 20-200 Torr of N2 diluent at 298 K. The rate constant of the reaction of NO3+CH3l is determined to be (4.1plus over minus 0.2)*10(super -13) cm(super 3) molecule(super -1) s(super -1) in 100 Torr of N2 diluent at 298 K and is pressure-independent.

The reactions of C1 atoms with XCH(sub 2)I (X=H, CH(sub 3), C1, Br, I) were studied using cavity ring-down spectroscopy in 25-125 Torr total pressure of N(sub 2) diluent at 250K. Absorption attributable to the formation of the XCH(sub 2)I-C1 adduct following the reaction of C1 atoms with XCH(sub 2)I (X=H, CH(sub 3), C1, Br, I) was measured as a function of temperature over the range 250-320 K.

An attempt is made to investigate the rate constants and the IO yield for the reaction of CH2I with O2 by monitoring the absorption of IO radicals with cavity ring-down spectroscopy (CRDS). Results suggest that the two-body reaction mechanism is dominant in CH2I + O2, or possibly the CH2IO2 formation path reaches already its high-pressure limit with a very limited yield.

This paper reports the results of processes resulting in D0u+-X 1Σg+ emission when a single rovibrational level of the E0g+ state is prepared. Our study reveals that two kinds of processes populate the D0u+ state; which one occurs depends on the experimental conditions. One process involves amplified spontaneous emission from the E0g+ 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 D0u+ state from a given rovibrational level of the E0g+ state. The discrepancy between our results and previous results for the E0g+→D0u+ relaxation is briefly discussed. [ABSTRACT FROM AUTHOR]

We report the analysis of the 2g(1D) ion-pair state of I2 by perturbation-facilitated optical-optical double resonance. The present study began with the observation of the 2g(1D)–A′ 3Π(2u) emission at around 230 nm during the analysis of the ultraviolet emissions originating form the 1u(1D) ion-pair state. The identification of this new transition helped us to specify the wavelengths for detecting the 2g(1D) state by emission, and also to estimate its absolute position. The intermediate states used to observe the 2g(1D) state were the B 3Π(0u+)–b′ 2u mixed states by the hyperfine interaction, which allowed us to combine the X 1Σg+ ground state with the 2g(1D) state in the (1+1) photon excitation following the optical selection rules for one-photon transitions: 2g(1D)←b′ 2u–B 3Π(0u+)←X 1Σg+. Our analysis covered the 2g(1D) state in the 0≤v≤12 and 9≤J≤40 ranges. The molecular constants and Rydberg–Klein–Rees (RKR) potential of the 2g(1D) state were reported. We discussed the occurrence of the 2g(1D)–A′ 3Π(2u) emission, when exciting to the 1u(1D) v=0 state, and attributed it to the g/u mixing between the 2g(1D) and 1u(1D) states by the hyperfine interaction. The effect of the perturbation on measured line intensities and lifetimes was evident. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The state-resolved and isotope-specific detection of nascent C10 generated from the photodissociation of Cl[sub 2]O 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 Cl0 is performed by observing single-color two photon laser-induced fluorescence. The REMPI spectrum is assigned to the ClO(C² Σ[sup -],υ'=O←X²Π[sub ω], υ = 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 ²Π[sub &frac32;] spin-orbit state is preferred: p(²Π3[sub ½]): P(²Π[sub &frac32;]) = 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 state is assigned to a ¹B[sub 2] ← ¹ A[sub 1] transition, in agreement with recent ab initio calculations. The measured β value is smaller than the limiting value of 1.0, suggesting dynamic reasons and simultaneous excitation to more than one PES. A fast and direct fragmentation process is deduced, where the upper limit for the lifetime of the excited dissociative state is calculated to be 300 fs. [ABSTRACT FROM AUTHOR]

The reactions of iodine monoxide radical, IO with alkyl peroxide radicals, RO2 (R = CH3, C2H5, and CF3), are studied using cavity ring-down spectroscopy. The rate constant of the reaction of IO with CH3O2 is determined to be (7.0 + 3.0) x [10.sup.-11] cubic centimeters [molecule.sup.-1] [s.sup.-1] at 298 K and 100 Torr of N2 diluent, which could apply to atmospheric modeling in the marine boundary layer.

The adduct formation in the reactions of Cl and Br atom with dimethyl sulfide (DMS) is studied theoretically and experimentally. The rate constants of the forward reaction at several temperatures and pressures are determined from the rise and decay time profiles of the adduct Cl-DMS using cavity ring-down laser spectroscopy.

The reaction of IO radicals with dimethyl sulfide is studied using cavity ring-down laser spectroscopy. The reaction rate constant shows both a temperature and pressure dependence.

We report the first observation of collision induced state-to-state energy transfer from the 2u (1D2) (v2u = 3–7) ion-pair state of I2 using a perturbation facilitated optical–optical double resonance technique through the c 1Πg∼ B 3Π(0+u) hyperfine mixed double-faced valence state as the intermediate state. The excitation of the 2u (1D2) state yielded the weak UV fluorescence from the wide range of vibrational levels in the nearby 2g (1D2) state. The vibrational distribution in the 2g (1D2) state derived by the Franck–Condon simulation of the UV fluorescence showed that the population in the 2u (1D2) state transfers mostly to the 2g (1D2) vibronic levels which are located energetically above the laser-prepared level. The radiative lifetimes and the self-quenching rate constants were determined to be 21.3 ± 0.1 and 44.6 ± 0.8 ns, and (1.30 ± 0.01) × 10−9 and (2.26 ± 0.17) × 10−9 cm3 molecule−1 s−1 for the 2u (1D2) (v2u = 3) and 2g (1D2) (v2g = 5) states, respectively. The rate constant for the 2u (1D2) – 2g (1D2) collision induced state-to-state energy transfer was also evaluated to be (1.89 ± 0.01), (3.07 ± 0.07), and (3.77 ± 0.05) × 10−10 cm3 molecule−1 s−1 for the v2u = 3, 5, and 7 levels, respectively. The very large self-quenching cross sections for the ion-pair states of I2 could be explained by the harpoon mechanism. [ABSTRACT FROM AUTHOR]