Ultrafast investigations of vibrationally hot molecules after internal conversion in solution

✍ Scribed by W. Wild; A. Seilmeier; N.H. Gottfried; W. Kaiser

• Publisher: Elsevier Science
• Year: 1985
• Tongue: English
• Weight: 396 KB
• Volume: 119
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(85)80413-9

✦ Synopsis

After electronic excitation most organic molecules return to the electronic ground state via radiationless processes. Internal conversion is one of the most important relaxation mechanisms. Usually, internal conversion rates are investigated by time-resolved bleaching experiments where the absorption recovery is monitored. These experiments only give information on the time the molecules require to return from the excited to the ground electromc state. The state of the molecules after internal conversion is not studied in most cases. After lntemal conversion the energy still resides in the individual molecule. Anharmonic coupling leads to a redistribution of energy over the many degrees of freedom. The vibrational excess energy may be related to an increase of internal temperature. Different absorption and fluorescence spectra are observed m steady-state experiments depending upon the internal temperature of molecules in the gas phase [l]_ Absorption changes have also been used to measure the deactivation of vibrationally highly excited molecules in gas-phase experiments on a microsecond time scale PI-Recently, we have introduced an ultrafast molecular thermometer which aIlows us to measure transient internal temperatures of molecules on a picosecond time scale [3,4] _ The instantaneous excess population of vibrational states or the internal temperature of the molecule is monitored via absorption changes at the long-wavelength edge of the S, absorption. This