Excitation of Bi, Bi2 and BiO via multiple collisions with singlet molecular oxygen

Chemiexcitation of metastable electronic states of atoms and small molecules has been suggested as a means of achieving efficient, cw laser operation in the visible (and near-IR and UV) wavelength region. The present research is part of an ongoing effort aimed at providing guidelines for obtaining excitation of metastable states via collisions with singlet molecular oxygen. The low excited states of the bismuth atom, belonging to the p3 ground-state configuration, are metastable with transition probabilities ⩽120 s−1. These metastable states can be populated as a result of one to three fruitful collisions of a ground state atom with an O2(1Δ) (E = 7882 cm−1) and/or O2(1∑) (E = 13,121 cm−1) molecules. Some of these collisional energy transfer steps are highly resonant. O2 (1Δ) and (1∑) can similarly populate electronic states of Bi2 and BiO. This paper reports on preliminary studies of reactions of O2(1Δ) and (1∑) with Bi vapor. Mechanisms for production of excited species in Bi/O2 mixtures are inferred from the dependence of the intensity of the emission from these species on the concentration of Bi atoms and Bi2 molecules.</jats:p

Generation of Photocurrents by Bis-aniline-Cross-Linked Pt Nanoparticle/Photosystem I Composites on Electrodes

Pt nanocrystals are implanted into photosystem I (PSI) by a photochemical reaction. The PSI with the associated Pt nanoclusters was modified with thioaniline and electropolymerized with thioaniline-functionalized Pt nanoparticles (NPs) to yield a bis-aniline-cross-linked PSI/Pt NPs composite. The alignment of the PSI with respect to the Pt NPs leads to effective charge separation and to generation of a photocurrent, ϕ (λ = 420 nm) = 2.6%, IPCE ∼ 0.35%. The bis-aniline units cross-linking the PSI/Pt NPs composite exhibit quasireversible redox features (E0′ = 0.05 V vs Ag/AgCl, at pH = 7.4). Biasing the electrode potential, E > 0.1 V vs SCE, results in the formation of the oxidized quinoid bis-aniline state that acts as an electron acceptor. At this applied potential, the bridges mediate the electron transfer to the electrode, resulting in a ∼10-fold higher photocurrent, as compared to the system that includes the reduced bis-aniline bridging units. Furthermore, the ferredoxin (Fd) electron relay was modified with thioaniline units and incorporated into the PSI/Pt NP composite during the electropolymerization process. The Fd bound to the matrix mediates the electron transfer toward the electrode and facilitates charge separation that results in enhanced generation of the photocurrent, ϕ (λ = 420 nm) = 3.8%, IPCE ∼ 0.5%