Knowledge Bank

The electronic spectrum of benzylidenecyclobutanc seeded in a supersonic jet expansion was recorded using resonantly enhanced two-photon ionization spectroscopy. [FIGURE] The main vibronic features in the spectrum belong to a low frequency progression assigned to the torsional motion of the phenyl ring. Several other low frequency modes were also observed. These were assigned by comparison with the spectra of several deuterated isotopomers in conjunction with ab initio calculations. The phenyl torsional potential was determined to have a minimum in the first excited singlet state corresponding to a planar conformation, while the ground state surface was characterized by a nonzero equilibrium torsional angle and a puckered cyclobutanc ring.