Nanosecond time-resolved EPR in pulse radiolysis via the spin echo method

Journal Article · Sat Dec 01 04:00:00 EST 1979 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.438243· OSTI ID:5977464

Trifunac, A D; Norris, J R; Lawler, R G

The design and operation of a time-resolved electron spin echo spectrometer suitable for detecting transient radicals produced by 3 MeV electron radiolysis is described. Two modes of operation are available: Field swept mode which generates a normal EPR spectrum and kinetic mode in which the time dependence of a single EPR line is monitored. Techniques which may be used to minimize the effects of nonideal microwave pulses and overlapping sample tube signals are described. The principal advantages of the spin echo method over other time-resolved EPR methods are: (1) Improved time resolution (presently approx.30--50 nsec) allows monitoring of fast changes in EPR signals of transient radicals, (2) Lower susceptibility to interference between the EPR signal and the electron beam pulse at short times, and (3) Lack of dependence of transient signals on microwave field amplitude or static field inhomogeneity at short times. The performance of the instrument is illustrated using CIDEP from acetate radical formed in pulsed radiolysis of aqueous solutions of potassium acetate. The relaxation time and CIDEP enhancement factor obtained for this radical using the spin echo method compare favorably with previous determinations using direct detection EPR. Radical decay rates yield estimates of initial radical concentrations of 10/sup -4/10/sup -3/M per electron pulse. The Bloch equations are solved to give an expression for the echo signal for samples exhibiting CIDEP using arbitrary microwave pulse widths and distributions of Larmor frequencies. Conditions are discussed under which the time-dependent signal would be distorted by deviations from an ideal nonselective 90/sup 0/--tau--180/sup 0/ pulse sequence.

• Research Organization: Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439
• OSTI ID: 5977464
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 71:11; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400600* -- Radiation Chemistry
440000 -- Instrumentation
47 OTHER INSTRUMENTATION
BEAMS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
DECOMPOSITION
DESIGN
ELECTRON BEAMS
ELECTRON SPIN RESONANCE
ENERGY RANGE
EPR SPECTROMETERS
IRRADIATION
LEPTON BEAMS
MAGNETIC RESONANCE
MEASURING INSTRUMENTS
MEV RANGE
MEV RANGE 01-10
OPERATION
PARTICLE BEAMS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIOLYSIS
RESONANCE
SPECTROMETERS
SPIN ECHO