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CP: Chemische Physik

CP 7: Spektroskopie

CP 7.4: Vortrag

Montag, 22. März 1999, 14:45–15:00, Gg

Spin and Molecular Dynamics of Biradicals at Variable Temperature — •Alexandra Yurkovskaya¹, Stefan Grosse², Sergeij Dvinskikh³, Olga Morozova¹, and Hans-Martin Vieth² — ¹International Tomography Center, Institutskaya 3a, 630090 Novosibirsk-90, Russia — ²FU-Berlin, Institut fü Experimentalphysik, Arnimalle 14, 14195 Berlin — ³Institut für Physik, Universität St.Petersburg

1H and 13C Chemically Induced Dynamic Nuclear Polarization

(CIDNP) and time resolved Stimulated Nuclear Polarization (SNP)

have been applied to the investigation of spin and molecular

dynamics of two consecutive biradical stages, the primary

acyl-alkyl and the secondary bis-alkyl biradical generated in

the photolysis of 2,2,12,12-tetramethyl-cyclododecanone, at low

magnetic field in the temperature range from 200 to 360 K.

Calculations have been performed based on the numerical solution

of the stochastic Liouville equation for the biradical spin

density matrix for the description of the spin and molecular

dynamics and take into account the distance dependence of the

exchange interaction. Good quantitative agreement between the

calculations and experimental data is found for the whole

temperature range when using the appropriate dependence of some

of the parameters on temperature. The model calculations

qualitatively confirm that the low temperature broadening of the

CIDNP field dependencies and the increase of the SNP decay time

are caused by the slowing down of the molecular mobility and the

decreasing of reactivity.