OPTICAL AND ODMR INVESTIGATION OF THE LOW-LYING EXCITED-STATES OF NEAT ALPHA-OXALIC ACID DIHYDRATE

The lowest excited singlet and triplet states of neat α-oxalic acid dihydrate have been investigated by optical, optical Zeeman, and zero-field optically detected magnetic resonance (ODMR) spectroscopy at T ≲ 4 K. The observed electronic transitions in absorption are assigned as 1Au ← 1Ag (ν0 = 34131 cm-1) from its normal polarizatio These correspond to the expected lowest lying 1,3nπ* excitations in trans-α-dicarbonyls. The 3Au → 1Ag phosphorescence is also observed. Monitoring the phosphorescence intensity, the fine structure splittings and principal axes' orientation and the kinetic parameters of the 3Au s The fine structure constants are X = 2510.0, Y = -1800.3, and Z = -709.7 MHZ where the x axis is in-plane and parallel to the carbo The absolute signs of the constants have been established by optical Zeeman measurements. The τx zero-field spin state has the largest total phosphorescence rate, radiative rate, and populating rate. The τx activity in the 0 - 0 band is polarized mainly along the x axis. However, considerable normal polarization associated with an in-p. © 1979.