Pulsed Laser Thermal Lens Spectrophotometry of Liquid Samples Using an Optical Fiber Beam Guidewith Interference Orthogonal Signal Processing

An apparatus for thermal lens spectrophotometry of liquid samples is conshucted using a pulsed nitrogen laser excitation source and a heliium-neon laser probe. Both laser beams are passed through a fused silica optlcal fiber prlor to being tightly focused Into the sample cell. The optical flber is used to reduce mode and pointng varlatlons in the laser outputs. A dlgltal correlation filter is developed and used for estlmatlon of the thermal lens signal. This dlgltal estimation procedure exhlblts a considerably enhanced slgnal-to-nolse ratio over that of other estimation methods. Moreover, It is relatively Immune to background Interference and rapid In estlmatlon time. Finally, the effectlve sample path length for focused beams In pulsed laser exclted thermal lens spectrophotometry is examlned from a theoretical basis. It is found that the slgnal will be very near maximum for cell path lengths on the order of 4 times the Raylelgh range

Temperature Dependence of the HO\u3csub\u3e2\u3c/sub\u3e + ClO Reaction. 1. Reaction Kinetics by Pulsed Photolysis-Ultraviolet Absorption and ab Initio Studies of the Potential Surface

The kinetics of the HO2 + ClO reaction was studied using the flash photolysis/ultraviolet absorption technique over the temperature range 203-364 K and pressure range 50-700 Torr of N2. In contrast to previous work, the temperature dependence displayed linear Arrhenius behavior over the entire temperature range with the rate constant being described by the expression k(T) = 2.84 × 10-12 exp{(312 ± 60)/T} cm3 molecule-1 s-1. Ab initio calculations of intermediates and transition states have been carried out on the singlet and triplet potential energy surfaces. These calculations show that the reaction proceeds mainly through the ClO-HO2 complex on the triplet surface; however, collisionally stabilized HOOOCl formed on the singlet surface will possess an appreciable lifetime due to large barriers toward decomposition to HCl and HOCl. Termolecular rate calculations using ab initio parameters lead to a strong collision rate constant of ∼5 × 10-32 cm6 molecule-2 s-1 for HOOOCl formation. This intermediate may be important under both laboratory and atmospheric conditions

Temperature Dependence of the HO_2 + ClO Reaction. 1. Reaction Kinetics by Pulsed Photolysis-Ultraviolet Absorption and ab Initio Studies of the Potential Surface

The kinetics of the HO_2 + ClO reaction was studied using the flash photolysis/ultraviolet absorption technique over the temperature range 203−364 K and pressure range 50−700 Torr of N_2. In contrast to previous work, the temperature dependence displayed linear Arrhenius behavior over the entire temperature range with the rate constant being described by the expression k(T) = 2.84 × 10^(-12) exp{(312 ± 60)/T} cm^3 molecule^(-1) s^(-1). Ab initio calculations of intermediates and transition states have been carried out on the singlet and triplet potential energy surfaces. These calculations show that the reaction proceeds mainly through the ClO−HO_2 complex on the triplet surface; however, collisionally stabilized HOOOCl formed on the singlet surface will possess an appreciable lifetime due to large barriers toward decomposition to HCl and HOCl. Termolecular rate calculations using ab initio parameters lead to a strong collision rate constant of ∼5 × 10^(-32) cm^6 molecule^(-2) s^(-1) for HOOOCl formation. This intermediate may be important under both laboratory and atmospheric conditions