Theg-Factor Anisotropy of Plant Chlorophylla•+

High-field EPR experiments at 12 T /330 GHz were performed on chlorophyll a radical cations in methylene chloride at low temperatures. Using fully deuterated chlorophyll it was possible to obtain the principal components of the rhombic g -tensor as g α = 2.00329 ± (5 × 10 -5 ), g β = 2.00275 ± (8 × 10 -5 ), and g γ = 2.00220 ± (8 × 10 -5 ). Protonated chlorophyll radicals did not give enough spectral resolution to yield the g -anisotropy from the EPR spectrum. This was true even at higher field/frequency combinations up to 24 T /670 GHz. Semiempirical calculations were performed using the INDO/S method (ZINDO) which yielded good agreement with the experimental data.