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.

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 have applied cavity ring-down spectroscopy 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 + CH3I was determined to be (4.1 ± 0.2) × 10-13 cm3 molecule-1 s-1 in 100 Torr of N2 diluent at 298 K and is pressure-independent. This reaction may significantly contribute to the formation of reactive iodine compounds in the atmosphere. [ABSTRACT FROM AUTHOR]

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 high-pressure limit rate constant for the Cl−DMS adduct formation is determined to be k1a(high) = (2.2 ± 0.2) × 10-10 cm3 molecule-1 s-1. The rate constant of Cl with DMS at atmospheric pressure is k1 = (3.6 ± 0.2) × 10-10 cm3 molecule-1 s-1. Error bars are 1σ. The Arrhenius plot of the forward reaction has a negative temperature dependence for 278−318 K. The calculated equilibrium constants of the reaction Cl and Br with DMS at 300 K are KClDMS = 2.8 × 10-12 and KBrDMS = 7.7 × 10-15 cm3 molecule-1, respectively. The binding energy (D0) is calculated to be 17.7 kcal mol-1 for Cl−DMS, and 14.1 kcal mol-1 for Br−DMS. D0(Br−C) is in fair agreement with the previously reported experimental value, 12 ± 1 kcal mol-1. The results are discussed in comparison with previous experimental reports of the bromine atom adduct, Br−DMS. Atmospheric implications regarding the fate of the X−DMS adducts (X = Cl and Br) in the troposphere are discussed. [ABSTRACT FROM AUTHOR]

Purpose: To clarify the presence or absence of differences in path pattern and movement during mastication between the habitual and non-habitual chewing sides., Methods: Participants were 225 healthy adults with natural dentition. Mandibular movement while chewing gummy jelly on each side was recorded, and masticatory path pattern was classified into five types (one normal and four abnormal). The frequency of each pattern was measured and compared between chewing sides. The amount, rhythm, velocity, and stability of movement and masticatory performance were measured and compared between chewing sides., Results: A normal pattern was observed on the habitual chewing side in 84.4% of participants. There was a significant difference between chewing sides in masticatory path pattern (χ 2 = 35.971, P < 0.001). Values of parameters regarding the amount and velocity of movement and masticatory performance were significantly higher on the habitual chewing side. Values of parameters regarding rhythm and stability of movement were significantly lower on the habitual chewing side., Conclusion: The present findings of functional differences between chewing sides in terms of path pattern and movement during mastication suggest that these factors should be analyzed on the habitual chewing side.

In this paper, we describe amplified spontaneous emission (ASE) from the f ' 0 g + ( 1 D 2 ) ion-pair state of I 2 populated through a two-step laser excitation technique via the B 3 Π(0 u + ) valence state. The intense infrared emission propagating in the direction of the incident laser beam is assigned to the ASE transition from the f ' 0 g + ( 1 D 2 ) state to the F ' 0 u + ( 1 D 2 ) ion-pair state. The subsequent ultraviolet fluorescence transition from the F ' 0 u + ( 1 D 2 ) state to the 0 g + ( bb ) state as well as the 0 g + ( ab ) state is also reported. By Franck-Condon simulation of the cascading F ' 0 u + ( 1 D 2 ) → 0 g + ( bb ) band, we determine the population distributions in the F ' 0 u + ( 1 D 2 ) state generated by ASE, which are consistent with the intensity profile of the mid-infrared ASE spectrum. Finally, employing these vibrational distributions for the F ' 0 u + ( 1 D 2 ) state, spectral parameters for the shallow 0 g + ( ab ) state are derived.