Mark Sharnoff

Electron spin resonance and the non-bonding orbitals of the phosphorescent state of pyrazine☆

Abstract We have used a microwave-optical double quantum method to investigate the electron spin resonance of the phosphorescent state of pyrazine as a guest in paradichlorbenzene. The fine structure tensor of pyrazine has approximate axial symmetry about the in-plane axis normal to the N-N direction. The fine structuer parameters are D = −(0.309 ± 0.001) cm−1 and E = +(0.006 ± 0.002) cm−1.

Electron Spin Resonance of the Triplet State of a Photochemical Oxidation Product of Crystalline Durene

Abstract An optical method of detection of electron spin resonance of metastable states has permitted the investigation of the triplet entity responsible for the blue component in the phosphorescence of purified crystalline durene. This entity has fine structure parameters and D/hc = ±(0.335 ± 0.003) cm−1 E/hc = ∓ (0.043 ± 0.002) cm−1 The principal axes of the fine structure tensor and the magnitudes of its principal values are consistent with Sponer and Kandas attribution of this phosphorescence to an aldehydic photo-oxidation product of the durene molecule.

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.

Photoselective determination of the magnetic axes of pyrazine

Abstract By photoselective excitation of pyrazine molecules randomly oriented in rigid glassy solvents and magnetoselective optical detection of their triplet state EPR, we have confirmed an earlier assignment of the principal axes of the magnetic fine structure tensor.

Microwave-Optical Double Resonance Investigation of the ESR of Metastable Triplet States

Abstract X band microwave-optical double resonance studies of the metastable triplet states of naphthalene-d 8 and quinoxalene are presented and the amplitudes and linebreadths of the signals examined. It is noted that the amplitudes of the lines are consistently an order of magnitude or more smaller than expected on the basis of a simple theory; the discrepancy is shown to arise in part from the long triplet spin-lattice relaxation times which prevailed under the conditions of the measurements. K band microwave optical double resonance results for quinoxalene support this analysis and indicate that the double resonance method can be extended to permit study of the ESR of triplet systems of photochemical interest which are too short-lived to be observable by conventional ESR methods. A successful application of the double resonance method to triplet cyclopentanone is reported.

Migration of Triplet Excitons in Benzophenone: A persistent coherence

Abstract Magnetic resonance profiles of triplet excitons in ultrapure orthorhombic benzophenone at liquid helium temperatures are presented. A band-structural theory which accounts for all the major features of these profiles is given in outline form. Phosphorescence decay data and excitonic spin-lattice relaxation data are brought into the analysis, and the behavior of the excitons is seen to be very nearly free of extrinsic influence. The magnetic resonance profiles are then recognized as characteristic of excitations which make their way coherently through a lattice with whose vibrations they strongly interact.

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.

Microscopic mapping of subnanometric motion.

The sensitivity of a microscope-based holographic system designed for mapping the motion of components of a living cell is calibrated by means of a simple procedure. Bubbles of air are allowed to drift with known velocity in a nearly horizontal, glycerine-filled capillary observed through the microscope. The ultrafine motion of the bubbles is captured interferometrically by subtractive superposition of a pair of holograms recorded a few milliseconds apart. Stationary portions of the field of view are rendered dimly in images reconstructed from the interferogram, while the brightness of moving portions varies monotonically with their displacement. Displacements as small as 1.1 nm were betrayed in the images. Analysis of the experimental conditions suggests that bubble displacements as small as 0.7 nm will become detectable once minor improvements are made in the apparatus.

Radiative and radiationless triplet exciton decay in benzophenone

Abstract The EPR of triplet excitons and of shallow triplet traps in crystalline benzophenone is observed by an optical detection technique. The predominantly radiationless mode of de-excitation of the traps is demonstrated and shown to account for most of the quenching of electronic excitation energy in this system.