We report observations by the Voyager 1 and 2 spacecraft of low-frequency magnetic waves excited by newborn interstellar pickup ions H + and He + during 1978-1979 when the spacecraft were in the range from 2 to 6.3 au. The waves have the expected association with the cyclotron frequency of the source ions, are left-hand polarized in the spacecraft frame, and have minimum variance directions that are quasi-parallel to the local mean magnetic field. There is one exception to this in that one wave event that is excited by pickup H + is right-hand polarized in the spacecraft frame, but similar exceptions have been reported by Cannon et al. and remain unexplained. We apply the theory of Lee & Ip that predicts the energy spectrum of the waves and then compare growth rates with turbulent cascade rates under the assumption that turbulence acts to destroy the enhanced wave activity and transport the associated energy to smaller scales where dissipation heats the background plasma. As with Cannon et al., we find that the ability to observe the waves depends on the ambient turbulence being weak when compared with growth rates, thereby allowing sustained wave growth. This analysis implies that the coupled processes of pitch-angle scattering and wave generation are continuously associated with newly ionized pickup ions, despite the fact that the waves themselves may not be directly observable. When waves are not observed, but wave excitation can be argued to be present, the wave energy is simply absorbed by the turbulence at a rate that prevents significant accumulation. In this way, the kinetic process of wave excitation by scattering of newborn ions continues to heat the plasma without producing observable wave energy. These findings support theoretical models that invoke efficient scattering of new pickup ions, leading to turbulent driving in the outer solar wind and in the IBEX ribbon beyond the heliopause.

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We report observations of low-frequency waves at 1 au by the magnetic field instrument on the Advanced Composition Explorer (ACE/MAG) and show evidence that they arise due to newborn interstellar pickup He+. Twenty-five events are studied. They possess the generally predicted attributes: spacecraft-frame frequencies slightly greater than the He+ cyclotron frequency, left-hand polarization in the spacecraft frame, and transverse fluctuations with minimum variance directions that are quasi-parallel to the mean magnetic field. Their occurrence spans the first 18 years of ACE operations, with no more than 3 such observations in any given year. Thus, the events are relatively rare. As with past observations by the Ulysses and Voyager spacecraft, we argue that the waves are seen only when the background turbulence is sufficiently weak as to allow for the slow accumulation of wave energy over many hours.

Photoejection of electrons from pyrenide ions (π. - ) or sodium pyrenide ion pairs (π. - , Na + ) was effected in tetrahydrofuran (THF) or tetrahydropyran (THP) solution by flash of light (λ > 420 nm). As the reaction was performed in the presence of a large excess of biphenyl (B) the ejected electrons were captured preferentially by that hydrocarbon reducing it to biphenylide radical ion (B. - or B. - , Na + ). Due to the low concentration of pyrene (π) the subsequent reactions between biphenylide and pyrene, namely B. - + π ( k 1 →) B + π. - (1) and B. - , Na + + π ( k 2 →) B + π. - , Na + , (2) could be easily monitored after the flash. By varying the ratio of [B. - ]/[B. - , Na + ] it was possible to make either (1) or (2) dominant, and hence to determine the rate constants k 1 and k 2 . Thus, k 1 = (4.8 ± 0.5) x 10 10 1 mol -1 s -1 and k 2 = 0.6 x 10 10 1 mol -1 s -1 for the electron transfer in THF, and k 2 = 0.5 x 10 10 1 mol -1 s -1 for the reaction in THP, all the constants referring to ≈ 20 °C.

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