Abstract

A tuneable dye laser was used to study the energy-level structure near the dissociation limit of the BΠ3o,u+ state of I2. The laser was continuously scanned from 498.0 to 520.0 nm while irradiating iodine vapor. Use of a wide-band filter, selected to pass only the third Stokes line of the fluorescence over the range of the laser scan, resulted in a continuous plot of the energy-level structure from about 35 vibrational levels below the dissociation limit to beyond the dissociation limit. From the spectrum, a value for the dissociation energy of the BΠ3o,u+ state was determined, corresponding to λ = 498.8 ± 0.3 nm, in agreement with recent absorption-spectroscopy experiments. The laser was then set at each of two wavelengths: 517.1 nm, well below the dissociation limit, and 501.2 nm, close to the dissociation limit; the absolute self-quenching and foreign-gas (N2) quenching cross sections for I2 were measured by use of a digital detection system. The results were Stern-Volmer plots that yielded values of σ2τ, where πσ2 is the quenching cross section and τ is the lifetime. Cross sections are reported on the basis of τ = 1.15 × 10−6 s. A surprisingly large background fluorescence, due to collisional excitation transfer, was superimposed on the line spectrum in the foreign-gas quenching data, but not for self-quenching; appropriate corrections therefore were required for the former. Values obtained for λ = 517.1 and 501.2 nm were, respectively, σself2=40±8 and 75 ± 15 Å2, σN22=3.7±1.0 and 15 ± 3 Å2.

© 1976 Optical Society of America

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