Vibronic Structure in the Fluorescence Lifetimes and Quantum Yields of Aniline Vapor

Abstract

Aniline vapor has a well‐resolved vibronic absorption spectrum in the region of the first excited singlet transition. By means of high‐resolution phase fluorimetry we have determined the spectrum of fluorescence lifetimes and quantum yields over the region from 300 to 275 nm with a bandwidth of 2.7 Å. The emission spectrum was not resolved. Relative values of quantum yields at different wavelengths were measured directly while absolute values were estimated from literature data. Quantum yields fluctuate between 0.3 and 0.6 and the reciprocal lifetime, $\text{1\hspace{0.17em}/\hspace{0.17em}τ}$ , varies in the range (1.3 to 2.3) × 10⁸ sec⁻¹. $\text{1\hspace{0.17em}/\hspace{0.17em}τ}$ shows sharply pointed minima whereas the quantum yields have maxima at the wavelengths of all major absorption peaks. The calculated intersystems crossing rate constants $k_{\mathrm{isc}}$ have minimum values at these wavelengths. These features are interpreted in terms of symmetry selection rules for spin–orbit and vibronic coupling.