Albert L. Shain

Static and dynamic paramagnetism of the undistorted triplet state of benzophenone

Existing discrepancies in reports of the EPR fine structure of triplet traps in uv‐excited benzophenone are clarified by studies of the population kinetics and the EPR of triplet benzophenone‐h10 in crystals of deuterobenzophenone. Benzophenone‐h10 provides a triplet trap of depth ≈30 cm−1 below the triplet exciton band of the deuterobenzophenone host and phosphoresces copiously at liquid helium temperatures. In deuterated crystals containing 1 mole% benzopheone‐h10, only the phosphorescence of ordinary benzophenone is detectible below 4.2°K; the quantum yield is 42%. The ordinary benzophenone traps are shown to have the same conformation as the triplet molecules formed by direct T1←S0 absorption and the molecules responsible for the excitonic phosphorescence of ordinary benzophenone crystals. The traps earlier reported by Sharnoff are shown to have nearly this conformation. The triplet states of the traps reported by Chan, Schmidt, Veeman, and van der Waals and by Winscom and Maki are shown not to have t...

Microwave-optical double resonance of the triplet state of cyclopentanone☆

Abstract Fine structure and hyperfine structure information on the chemically reactive 3nπ* state of cyclopentanone is obtained by the low field microwave-optical double resonance (MODOR) technique. The hyperfine structure is interpreted tentatively to indicate that the magnetic z axis lies perpendicular to the carbonyl bond and nearly parallel to the C5C1C2 plane. The principal values of the fine structure spin hamiltonian are D/hc = ±0.1404±0.0001 cm−1, E/hc = +- 0.0271 ± 0.0001 cm−1.

Transient effects in the microwave optical double resonance of cyclopentanone

Abstract We have observed microwave-driven inversion and recovery of the populations of the spin sublevels of the chemically reactive , n Π * triplet state of cyclopentanone at 77,4.2 and 1.4°K. By analyzing the transients in the phosphorescence, we have extracted the values of the kinetic parameters for the population and depopulation of the sublevels. The kinetics at 77°K are glossly different from those which prevail in the liquid helium temperature range.

Microwave—optical multiple resonance and dynamic interconversion of configurations in excited molecular states

Abstract Optically detected electron double resonance studies of excited molecules have brought to light two new phenomena: multiple, interconverting types of paramagnetism and multiple, interconverting types of luminescence. The multiple properties are characteristics of a single molecular state. Their interconversion occurs freely at temperatures as low as 1.4°K.

Optically detected multiple-quantum transitions in photoexcited molecular triplet states in zero external magnetic field

Abstract Multiple-quantum, microwave-driven transitions between zero-field spin sublevels of a photoexcited triplet state are observed and classified.