SIMPLE 2-PULSE DETECTION SCHEME IN PULSED EPR FOR STUDYING LOW-FREQUENCY NUCLEAR COHERENCES

A microwave two-pulse sequence with a weak and long 180 degrees first pulse and a hard 90 degrees second pulse is employed to detect nuclear coherences in pulsed EPR. The coherences created by the first pulse a re transferred after an evolution period T into an observable FID by t he second pulse. The free induction is measured at some fixed delay af ter the second pulse; it is modulated when T is varied. As the second pulse may be snitched on immediately after the first pulse, the nuclea r coherences may be detected immediately as they start to freely oscil late, without loss of information within the instrumental dead time. T he method is demonstrated for a sample of the radical cation of N-15-l abeled bacterio-chlorophyll a. (C) 1998 Academic Press.