X- and Y-Polarized Spectra of Chlorophyll a and Pheophytin a in the Red Region: Resolution Enhancement and Gaussian Deconvolution

Abstract

The red region of the X- and Y-polarized spectra obtained from the measurement of linear dichroism of chlorophyll a and pheophytin a oriented in a liquid crystal^-1 has been reexamined. A combination of resolution enhancement of the spectra involving their Fourier transformation and manipulation in the Fourier domain, and deconvolution into Gaussian bands on the wavenumber scale has produced results conforming to previous conclusions that place the origin of the Q_x transition in chlorophyll a some 800-900 cm-¹ to the blue relative to the origin of the Q_y transition. In pheophytin a, however, the separation between the Q_x and Q_Y bands is much larger, about 3600 cm^-l. The results also confirm previous reports of an angle near 70º between the transition moment directions of the Q_y transitions and the molecular X-axis for both chlorophyll a and pheophytin a. The resolved vibronic bands in the case of the Q_y transition of chlorophyll a, at least, have their counterparts in both solution spectra and high-resolution low-temperature fluorescence excitation spectra.