The interpretation of optically detected ENDOR in zero field and their relationship to N-14 nuclear quadrupole interactions in (3)(pi pi*) states of quinoline and quinoxaline

It is shown that the proper assignment of N-14 ENDOR transitions in azaaromatic pi, pi* triplet states must take into consideration the contribution of the electron magnetic moment operator to the intensity of a given transition. In quinoline and quinoxaline, the electron magnetic moment operator is found to give the dominant contribution to ENDOR intensities, and to a high degree of accuracy the nuclear moment operator may be neglected. An erroneous ENDOR assignment of quinoxaline is corrected on this basis, and the ENDOR of quinoline is assigned. In particular, we find for these molecules that the dominant ENDOR transitions do not yield the N-14 qudrupole parameters e(2)qQ and eta independently, but only the value of 3e(2)qQ (1-eta/3)/4.