The molecule 2,5-di-(2-benzoxazoly)phenol (DBP) has been studied by laser spectroscopy in a supersonic free jet.
In the jet the fluorescence with a Stokes shift of 7000 cm-1 arises exclusively from the proton-transferred species.
The fluorescence excitation spectrum of DBP exhibits the broad fluorescence background underlying some weak, sharp features.
The first prominent band has been observed at 27830 cm-1, but from 250 cm-1 above the origin the spectrum
becomes congested and broad. OH to OD substitution of DBP produces a blue shift of 103 cm-1. For the deuterated
sample (DBP-d1) resolved line structure in the fluorescence excitation spectrum has been observed up to an excess
energy of 400 cm-1. To identify spectral features corresponding to deuterated DBP and other species double-resonance
depletion spectroscopy has been applied. From analysis of the width of the vibronic bands of DBP-d1, we estimated
an upper limit of the excited state deuteron transfer rate constant, kPT=1.7*1012s-1.