The g-Factor Anisotropy of Plant Chlorophyll a•+

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 gα = 2.00329 ± (5 × 10-5), gβ = 2.00275 ± (8 × 10-5), and gγ = 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.