Study of the electron spin resonance of negative ions field emitted into liquid helium

Abstract

We report the unambiguous detection of the ESR signals of negative ions in liquid helium. The linewidth was measured to be 5.0 \ifmmode\pm\else\textpm\fi{} 0.4 mG, the $g$ value was found to be pressure independent and equal to the free-electron $g$ value to within 10 ppm, and ${T}_{1}$ was estimated to be greater than 100 msec. A theoretical framework has been developed which explains the microwave power and temperature dependence of the signal intensity and demonstrates the existence of an initial polarization at the time of formation of the bubble state. A striking dependence of this initial polarization on pressure was discovered. Studies have been made which apparently rule out the possibility that other species contributed to our observed signal. Extensive optical studies of a discharge region near the field emission tip have been carried out in an attempt to understand the mechanism responsible for the initial polarization. A correlation between the pressure dependences of the intensity of the ultraviolet radiation from the discharge region and the initial polarization was observed.