Effects of deuteriation on ZFS and sublevel decay rates of ³ππ* benzaldehyde

Abstract

We have investigated deuterium effects on the ZFS and the sublevel decay rates of ³ππ* benzaldehyde in three different hosts. It was found that deuteriation of the formyl hydrogen reduces D considerably in acetophenone and 1,4-dichlorobenzene hosts. This effect is explained in terms of the changes in the ³ππ*-³ nπ* energy separations.

The deuterium effect on the sublevel decay rate is likely due to two causes. (1) The ratio between the radiative decay rate constant (k_i ^r ) and the radiationless decay rate constant (k_i ⁿ ) is dependent on the sublevel. (2) k_i ⁿ is sublevel dependent. The deuterium effect on k_z ⁿ is shown to be very large in ³ππ* benzaldehyde.

The deuteriation of formyl hydrogen predominantly affects k_z ⁿ which indicates, as predicted by Kanamaru and Lim, that ³ππ*-³ nπ* vibronic mixing is the most important mechanism in causing the radiationless decay. The correlation between the z sublevel decay rate constant (k_z ) and ΔE_TT found for a series of benzaldehydes is discussed in the light of the present results.