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Laser photolysis experiments on carboxymethylated chitin derivatives, such as carboxymethyl chitin (CM-chitin) and carboxymethyl chitosan (CM-chitosan), in aqueous solution by a 248 nm excimer laser were carried out for the first time. The transient absorption spectra of photolyzed CM-chitin or CM-chitosan solutions revealed a strong band with the maximum at 720 nm, which was assigned to the hydrated electron (eaq^- ). In the presence of argon, the eaq^- decays by reacting with CM-chitin or CM-chitosan, and the rate constants are (6.1 ± 0.1) × 10⁷ M^-1 s^-1 and (3.7 ± 0.1) × 10⁷ M^-1 s^-1, respectively. Long-lived radicals with relatively weak absorption intensity were detected in the near-UV region. The absorption band was not notably characteristic and showed only an increasing absorption toward shorter wavelengths. It is similar to the signal of ^•CM-chitin or ^•CM-chitosan macroradicals formed by the reaction of CM-chitin or CM-chitosan with an OH^• radical. It was assigned to ^•CM-chitin^- or ^•CM-chitosan^- macroradicals formed by eaq^- + CM-chitin or CM-chitosan reaction. CM-chitin aqueous solutions were further examined by pulse radiolysis in order to confirm the site of the long-lived radical.

The reactions of OH^• or SO4^•- radicals with carboxymethyl chitin (CM-chitin) and its deacetylated product, carboxymethyl chitosan (CM-chitosan), were investigated in aqueous solutions using a laser photolysis technique. The rate constants of the reactions of OH^• and SO4^•- radicals with CM-chitosan are always higher than those for CM-chitin, indicating that the amino-group could increase the reactivity of carboxymethylated chitin derivatives. The rate of the reactions of CM-chitin and CM-chitosan with OH^• radical was found to decrease at lower pH when polymers chains tend to the coiled conformation. In comparison, the rate constant of the reaction of SO4^•- radicals with CM-chitin or CM-chitosan decreased with pH, indicating that CM-chitin or CM-chitosan has a higher reactivity with the SO4^•- radical at low pH due to the protonation of the amino group.

Theoretical expectation that excitonic molecules are generated directly by the two-photon absorption, has been confirmed experimentally in CuCl and CuBr crystals. The luminescence of the radiative decay of the excitonic molecule thus created directly is found to show a very sharp emission band which is attributable to the Bose condensation at K≈ 0. In connection with the sharp emission, the two-photon resonance Raman scattering is studied.

High resolution polarization rotation spectroscopy is performed to evaluate the third-order nonlinear susceptibility, | χ(3)|, associated with the giant two-photon absorption (GTA) of biexcitons in CuCl. The true width of the biexciton atK≈ 0 and | χ(3)| at the resonant peak are obtained to be 24 ± 2 μeV and (3.0 ± 0.9) × 10-4esu at the weakest excitation density of ⩽ 1 kW/cm2for a high quality crystal, respectively.

Abstract: Two-photon excitation spectra of photo-voltaic effects and relevant excitonic emissions of a naturally grown single crystal of Cu2O have been studied at 77 K and 2 K. The photo-voltaic effects have been detected under local excitation at a macroscopical distance apart from the electrodes. The participation of the yellow series excitons in the generation of the photo-voltaic signal has been discussed.