Radiationless transitions between excited singlet states of biacetyl

✍ Scribed by C. Richard; M. Bouchy; J. C. Andre; M. Niclause

• Publisher: John Wiley and Sons
• Year: 1978
• Tongue: English
• Weight: 577 KB
• Volume: 10
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550100207

✦ Synopsis

Emission processes from lower excited states S1 (fluorescence) and 2' 1 (phosphorescence) have been studied in the gas and liquid phases when biacetyl is excited into the second singlet state Sz. (In agreement with Kasha's rule no fluorescence is observed from the S2 state.)

In the liquid phase, when biacetyl is excited into the singlet states Sl and Sz, no difference is observed between these emission processes. This phenomenon certainly results from an efficient nonradiative transition between the second excited singlet state S Z and the first excited state S1 with practically no excess vibrational energy. The quantum yield of this transition is almost unity and does not depend on the nature of the solvent.

In the gas phase no emission processes are observed when biacetyl is excited into the S Z state at low pressure (less than 10 mm Hgf. High pressure of inert gas is necessary in order to observe these processes. As for excitation into the S I state with vibrational energy, loss of vibrational energy through collisions occurs from the S2 state. The quantum yield of the S Z -SI transition by excitation a t 290 nm is estimated around 0.5-0.6 at 6 atm of inert gas (ethane, ethylene, or carbon dioxide).