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Photoionization spectroscopy and mass spectrometry of doped helium (He)nanodroplets rely on the ability to efficiently detect ions and/or electrons.Using a commercial quadrupole mass spectrometer and a photoelectron-photoioncoincidence (PEPICO) spectrometer, we systematically measure yields of ions andelectrons created in pure and doped He nanodroplets in a wide size range and intwo ionization regimes -- direct ionization and secondary ionization afterresonant photoexcitation of the droplets. For two different types of dopants(oxygen molecules, O$_2$, and lithium atoms, Li), we infer the optimal dropletsize to maximize the yield of ejected ions. When dopants are ionized bycharge-transfer to photoionized He nanodroplets, the highest yield of O$_2$ andLi ions is detected for a mean size of $\sim5\times10^4$ He atoms pernanodroplet. When dopants are Penning ionized via photoexcitation of the Hedroplets, the highest yield of O$_2$ and Li ions is detected for $\sim10^3$ and$\sim10^5$ He atoms per droplet, respectively. At optimum droplet sizes, thedetection efficiency of dopant ions in proportion to the number of primaryphotoabsorption events is up to 20\,\% for charge-transfer ionization of O$_2$and 2\,\% for Li, whereas for Penning ionization it is 1\,\% for O$_2$ and4\,\% for Li. Our results are instrumental in determining optimal conditionsfor mass spectrometric studies and photoionization spectroscopy of moleculesand complexes isolated in He nanodroplets.

Dopant ionization and efficiency of ion and electron ejection from helium nanodroplets