Single-molecule chemical reactions with individual single-walled carbon nanotubes were observed through near-infrared photoluminescence microscopy. The emission intensity within distinct submicrometer segments of single nanotubes changed in discrete steps after exposure to acid, base, or diazonium reactants. The steps were uncorrelated in space and time and reflected the quenching of mobile excitons at localized sites of reversible or irreversible chemical attack. Analysis of step amplitudes revealed an exciton diffusional range of about 90 nanometers, independent of nanotube structure. Each exciton visited about 10,000 atomic sites during its lifetime, providing highly efficient sensing of local chemical and physical perturbations.

Unimolecular pathways for the isomerization and/or dissociation of HSOO, HOSO, HSO 2 , and HOOS to H + SO 2 and OH + SO have been investigated computationally, as well as HSO formation via an HSOO intermediate. The atmospheric lifetime of HSO 2 is discussed. Some pathways have no barrier, including OH + SO f HOSO and H + SOO f HSOO and SOOH, while structures and vibrational frequencies of transition states for HOSO f H + SO 2 , HOOS f OH + SO, HOSO f HSO 2 , HSOO f HS + O 2 , and HSO 2 f H + SO 2 have been characterized at the MP2)FULL/6-31G(d) level. Some geometries were further refined at the QCISD/6-311G(d,p) level. Gaussian-2 theory was employed to calculate approximate QCISD(T)/6-311+G-(3df,2p) energy barriers, and the kinetics were analyzed by RRKM theory. Rate constant expressions at the high and low-pressure limits and thermochemical properties for transient intermediates are tabulated, and the results are discussed in the context of atmospheric and combustion chemistry. A revised theoretical H-OSO bond strength is compatible with the flame data for SO 2 -catalyzed recombination of H atoms.

Single-nanotube photometry was used to measure the product of absorption cross section and fluorescence quantum yield for 12 (n,m) structural species of semiconducting single-walled carbon nanotubes in aqueous SDBS suspension. These products ranged from 1.7 to 4.5 x 10(-19) cm(2)/C atom, generally increasing with optical band gap as described by the energy gap law. The findings suggest fluorescent quantum yields of approximately 8% for the brightest, (10,2) species and introduce the empirical calibration factors needed to deduce quantitative (n,m) distributions from bulk fluorimetric intensities.