Origin of Photoacoustic Signals in the Visible Spectrum of I₂ Vapour

Abstract

Vibronically resolved laser photoacoustic spectrum of I₂ vapour at room temperature in presence of air at atmospheric pressure has been recorded in the region 14700–20300 cm ⁻¹ for the first time. The bands are identified with the B ³ π (O u ⁺) ← X ¹ Σ _g ⁺ transition and evidence of energy transfer to atmospheric oxygen around 19700 cm⁻¹ region as well as predissociation around v’~23–27 have been observed. The relative intensities of nonradiative transitions have been estimated in the light of the Frank-Condon Factors (FCF’s) from optical absorption spectra and Boltzmann factors of the ground state vibrational levels. The entire spectrum has been divided into four parts on the basis of radiationless processes leading to the photoacoustic signals.