ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Intrinsic linewidths of the MJ=−1 to MJ=0 electron paramagnetic resonance (EPR) transitions of O2 for total rotational quantum numbers N=3, 5, and 7 were redetermined by the second harmonic zero crossing method using direct calibration of modulation depth and analytic accounting for the effect of harmonic distortion of the magnetic field modulation waveform. The collisional linewidths were found to be 4.38±0.05, 4.26±0.07, and 4.22±0.10 MHz/Torr, respectively, for N=3, 5, and 7, corresponding to relaxation/reorientation cross sections of 0.679, 0.661, and 0.655 nm2. Anomalous negative zero-pressure linewidths detected in an earlier study were also given by linear regression analysis of the present data at pressures over 0.5 Torr. Extending the pressure range down to 0.05 Torr using a voltage controlled oscillator (VCO) to mimic tracking gaussmeter signals showed that the linewidth does appear to extrapolate finally to a physically meaningful positive value at zero pressure. No satisfying interpretation of the measured intrinsic widths being approximately 200 kHz too small to yield physically meaningful linearly extrapolated zero-pressure widths was found.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.457066
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