K.V.S. RamaRao

Dual sites of solvation for electrons produced by photoionisation in aqueous micellar solutions

Laser flash photolysis of either aqueous micellar solutions of triton X-165 at 248 nm or of a probe phenothiazine (PTH) in triton X-165 or brij-35 micelles at 351 nm gives transient absorption peaks at 630 and 720 nm which are attributed to electrons solvated in the palisade region of the nonionic micelle and to electrons hydrated in bulk water. Picosecond studies show that, at the end of a 35 ps pulse, the electrons are already solvated, a major fraction of which undergo geminate recombination with the sibling cations. After 10 ns, both the 630 and 720 nm peaks are clearly seen.

Infrared multiphoton dissociation in focused laser beams: I. Generalization

Various models for IR multiphoton dissociation of polyatomic molecules in focused laser beams are discussed. To appreciate the fluence dependence of the dissociation yield, the essential laser beam characteristics, like its mode structure, propagation and focusing aspects are dealt with in some detail. Specific applications to isotope separation are discussed in a subsequent paper.

Isotope selective IR multiphoton dissociation in an efficient laser waveguide reactor

Abstract Isotope selective IR multiphoton dissociation (MPD) was investigated in a simple Pyrex glass waveguide (WG) reactor. Important theoretical and experimental studies were performed concerning the excitation-dependent transmission properties of the WG with a transverse electric atmosphere (TEA) CO 2 laser. From these studies, the WG parameters can be selected for efficient MPD. Various important aspects such as laser beam quality excitation of various WG modes, beam coupling in the WG and wall-induced breakdown or reaction, etc. are discussed. The WG reactor was initially operated with well-known systems such as SF 6 and CF 3 Br. The dissociation yield was several times larger than that obtained with a conventional cylindrical reactor, whereas the separation factor remained unchanged. Therefore the WG reactor can be used for isotope selective dissociation and the process parameters can be determined using fewer laser pulses even in a poor absorptive medium. Using this reactor, we report, for the first time T—D separation in CTF 3 —CDF 3 mixtures by exciting at the wings of CTF 3 absorption. Optimization of these reactors will eventually lead to a better utilization of laser photons and the reactor may then be integrated into full-scale separation plants.

Dual sites of solvation for the electrons and cation-electron recombination observed in the radiolysis of Triton X-100 and water mixtures: homogeneous and liquid crystalline regions

Abstract Pulse radiolysis studies were carried out on mixtures of a nonionic surfactant Triton X-100 (Tx) and water. In the range 40–70% Tx, two transient absorption peaks at 630 and 720 nm were observed due to the solvation of radiolytically generated excess electrons in the palisade layer of the surfactant pseudophase and in water. Transient absorption due to the cation radical and triplet state of Tx was also observed. On shorter timescales (∼ 300 ns) a strong emission with λ max =305 nm due to the singlet state of Tx was also seen, generated by recombination of the cation radical and electrons. Scavenging studies by nitrate ions and pyrene demonstrated a preferential picking up of electrons from aqueous and surfactant pseudophases, respectively.

PHOTOPHYSICAL AND PHOTOCHEMICAL PROPERTIES OF TRITON X‐165 IN AQUEOUS AND METHANOLIC SOLUTIONS

Abstract Laser flash photolysis of the nonionic surfactant Triton X‐165 was carried out at 248 nm in methanolic and aqueous solutions at different pHs. Cation radical, triplet, phenoxy radical and solvated electron were observed as the transient absorbing species. Various characteristics of these transient species and their decay constants are reported. Photoionization was found to be a major process and it was monophotonic. The results obtained are compared with the photolysis of a small molecule p‐methoxytoluene (PMT). Fluorescence and phosphorescence properties of the surfactants Triton X‐100, Triton X‐165 and PMT are also studied. A suitable reaction scheme is proposed to account for the observed results.

Infrared multiphoton dissociation in focused laser beams: II. Application to T/D/H isotope separation

Abstract In the preceding paper it was shown that multiphoton dissociation (MPD) yield vs fluence can be expressed by a “power-law” model. Here the model is exploited for the purpose of presenting and analysing our experimental data on T/D/H separation. This approach permits a unified description of the experimental system regardless of the potential complexities.

Separation of tritium from deuterium by pulsed NH3 laser-selective multiple photon dissociation of CTCl3

The multiple photon dissociation of ppm level CTCl3 in CDCl3 and the selectivity of T/D separation were investigated using a pulsed ammonia laser. The effect of laser frequency, fluence and buffer gas pressure on the dissociation rate and isotopic selectivity were studied. The depletion of CDCl3 was not observed within experimental errors. A lower limit of single step selectivity factor was found to be >5000 at 133 Pa substrate pressure.

Chemiluminescent reaction of oxygen atoms with carbon disulfide

Abstract Broad chemiluminescent emission from the O( 3 P)+CS 2 reaction was observed in the 300–450 nm region and was attributed to the B 3 Σ − u −X 3 Σ + u transition of S * 2 . First-order kinetics was observed in both reactants. The chemiluminescent rate constant, photon yield and utilization of exoergicity in chemiluminescence were estimated.

Laser induced decomposition of uranium tetrahydroborate

Electronic excitation of uranium tetrahydroborate, U(BH 4 ) 4 , results in the decomposition of the molecule. Longer wavelength excitation seems to induce a molecular collapse and a larger quantum yield of hydrogen.

Chemiluminescent reactions of some bromine-containing hydrocarbons with samarium under beam-gas conditions

Abstract Chemiluminescent reactions of samarium with bromine-containing hydrocarbons are reported under atomic beam—gas conditions. The chemiluminescent emission is in the visible region and is attributed to SmBr 2 emitter. The scattering and chemiluminescent cross-sections and photon yields are determined and compared with corresponding chloro analogues. The photon yields for the emitters are found to be in the order: SmBrCl > SmBr 2 > SmCl 2 . The total cross-sections are estimated from the known polarizabilities of the reactants using the Massey—Mohr expression and are compared with those observed. The fraction of the total exoergicity appearing as product electronic excitation is estimated and is found to be about 0.1%.