Molecular beam resonant two-photon ionization study of caffeine and its hydrated clusters.
We investigated electronically excited states of caffeine and its 1:1 complex with water by using resonant two-photon ionization (R2PI) and UV-UV hole-burning techniques. Strong vibronic coupling between a pair of close-lying pi-pi* and n-pi* transitions is proposed to be responsible for the broad spectral feature observed. By comparing the experimental results with those of theoretical calculations, both the O-bonded and N-bonded forms were suggested to be initially produced for the 1:1 complex. The electronic transitions of the O-bonded complex were blueshifted in the R2PI spectrum. For the N-bonded complex, the excited state undergoes an ultrafast decay process, followed by dissociation on a repulsive potential energy surface, which gives rise to a characteristically anomalous cluster distribution in nanosecond experiments.
Kim
Doory
D
Department of Chemistry, Seoul National University, Seoul 151-747, Korea.
Kim
Hyung Min
HM
Yang
Key Young
KY
Kim
Seong Keun
SK
Kim
Nam Joon
NJ
D002110:Caffeine / Q000737:chemistry* / Q000528:radiation effects*; D003198:Computer Simulation; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation / Q000528:radiation effects; D017785:Photons; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry*
D014867:Water; D002110:Caffeine