Single-rotational-level lifetimes from measurements of linewidths in the B3Π+←X1Σ+ system of ICI

Abstract

Lines in the 3−1 band of the B³Π_0⁺←X¹Σ⁺ system of ICl vapor havew been recorded using a Fabry–Perot interferometer spectrometer. A striking increase in linewidths is observed for transitions ending on excited‐state rotational levels above J′=37. Even at low J′, the linewidths are approximately twice the expected value. Examination of the probable causes of the broadening in the spectrum points to shortened excited‐state lifetimes and yields 3×10⁻¹¹ sec for the lifetime of I³⁵Cl in the J′=41 level and about 2×10⁻¹⁰ sec for J′ values below 20. These may be compared with the radiative lifetime, 9.8×10⁻⁷ sec, obtained from areas of some of the profiles measured here. The observed short lifetimes are discussed in terms of a homogeneous predissociation suggested also by earlier workers. The data require that the outer limb of the potential energy curve of the B state interact with an unstable O⁺ state. In addition it is suggested that a weaker, heterogeneous predissociation contributes to the widths for levels of low J′.