Photoabsorption and fluorescence spectroscopy of BF3 in the extreme-vacuum-ultraviolet region.

Abstract

Absorption and fluorescence cross sections of ${\mathrm{BF}}_{3}$ were measured in the 45--113-nm region. Partial ionization cross sections are derived from the absorption cross section and the known branching ratios and then compared with theoretical calculations. The absorption spectrum shows many vibrational progressions and broad bands that are attributed to the Rydberg and/or valence transitions. Fluorescence from excited ${\mathrm{BF}}_{2}^{\mathrm{*}}$ is observed from photoexcitation of ${\mathrm{BF}}_{3}$. The fluorescence quantum yield shows two repulsive excited states that give maximum yields of 34% at 88 nm and 20% at 96 nm. These two states produce four ${\mathrm{BF}}_{2}^{\mathrm{*}}$ emission bands that are distinguished by different fluorescence spectra and radiative lifetimes. The photoexcitation processes that lead to fluorescence and ionization are discussed.