EXCITED-STATE PROTON-TRANSFER IN JET-COOLED 2,5-DI-(2-BENZOXAZOLYL)PHENOL

The molecule 2,5-di-(2-benzoxazolyl)phenol (DBP) has been studied by l aser spectroscopy in a supersonic free jet. In the jet the fluorescenc e with a Stokes shift of 7000 cm(-1) arises exclusively from the proto n-transferred species. The fluorescence excitation spectrum of DBP exh ibits the broad fluorescence background underlying some weak, sharp fe atures. The first prominent band has been observed at 27830 cm(-1), bu t from 250 cm(-1) above the origin the spectrum becomes congested and broad. OH --> OD substitution of DBP produces a blue shift of 103 cm(- 1). For the deuterated sample (DBP-d(1)) resolved line structure in th e fluorescence excitation spectrum has been observed up to an excess e nergy of 400 cm(-1). To identify spectral features corresponding to de uterated DBP and other species double-resonance depletion spectroscopy has been applied. From analysis of the width of the vibronic bands of DBP-d(1), we estimated an upper limit of the excited state deuteron t ransfer rate constant, k(DT) = 1.7 x 10(12) s(-1). (C) 1998 Elsevier S cience B.V. All rights reserved.