A Spectroscopic Study of the Torsional Modes of
Torsional Modes of 1,4-bis(phenylethynyl)benzene
The CRDS experiment has been used to study the torsional vibrational modes of 1, 4-bis(phenylethynyl)benzene (BPEB).
Only the symmetric torsional vibration moves the central phenyl ring, thus isotopic substitution of the hydrogens on the central ring can be used to identify spectral peaks belonging to the individual modes.
UV-Vis Spectrum of BPEB
The UV-vis spectrum of BPEB in the gas phase was recorded and compared with the spectrum recorded on cyclohexane solution. Due to the 20 nm blue shift in the gas phase the CRDS experiment was targeted under the shoulder of the spectrum at 320 nm.
The CRDS experiment was modified to seed the molecular beam with BPEB. An 'oven' design was adapted for use in our system.
When heated the solid sample sublimes in the vacuum of the chamber and creates a cloud of BPEB vapour in the exit of the oven. When the nozzle is fired the Ar pulse 'picks-up' and cools the BPEB as it travels towards the ring-down cavity axis. The 40 deg cone in the oven aids cooling and spatial focusing of the beam.
This allowed us to record the spectra of BPEB and D-BPEB.
From the spectra, we were able to deduce the tortional potentials of the electronic ground and excited states and to successfully simulate the spectra.
The results of this study are published at:
Cavity Ring-Down Spectroscopy of the Torsional Motions of 1,4-Bis(phenylethynyl)benzene.
The article has been released on the web and can be downloaded by subscribers of ASC journals using the following link: 10.1021/jp054426h