Electronic relaxation processes in polyatomic molecules. Progress report, October 1, 1976--September 31, 1977

Technical Report · Thu Sep 01 04:00:00 EDT 1977

DOI:https://doi.org/10.2172/7078081· OSTI ID:7078081

Lim, E. C.

Experimental and theoretical studies of isotope and substituent effects on T/sub 1/ radiationless decay rates have been carried out as a test of the working hypothesis that vibronic coupling between n..pi..* and ..pi pi..* states lead to very efficient radiationless decay from the lower of the two vibronically coupled pair (proximity effect). In addition to providing general support to this hypothesis, the results indicate that isotope effects on spin sublevel decay rates are needed for a stringent test of the proximity effect. The radiationless decay rates of the /sup 3/B/sub 1g/ state of anthracene and its derivatives have been deduced from the quantum yield of /sup 3/B/sub 1g/ ..-->.. /sup 3/B/sub 2u/(T/sub 1/) fluorescence and the oscillator strength of /sup 3/B/sub 1g/ ..-->.. /sup 3/B/sub 2u/ absorption. The results suggest that there is a hitherto unrecognized triplet state (probably a /sup 3/B/sub 3u/) slightly below the /sup 3/B/sub 1g/, which has long been thought to be the second triplet state of the molecules. Very fast /sup 3/B/sub 1g/ ..-->.. /sup 3/B/sub 3u/ internal conversion, over a small energy gap, is proposed to ''drive'' intersystem crossing from the /sup 1/B/sub 2u/(S/sub 1/) state to the triplet manifold via a resonance mechanism. This proposal has important bearing on the understanding of the mechanisms for singlet ..-->.. triplet intersystem crossing in aromatic hydrocarbons.

• Research Organization: Wayne State Univ., Detroit, Mich. (USA)
• Sponsoring Organization: USDOE
• OSTI ID: 7078081
• Report Number(s): COO-2192-23
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ANTHRACENE
AROMATICS
CONDENSED AROMATICS
DE-EXCITATION
DEUTERIUM
ENERGY LEVELS
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
HYDROCARBONS
HYDROGEN ISOTOPES
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
RADIATIONLESS DECAY
STABLE ISOTOPES
VIBRATIONAL STATES