Cavity ring-down spectroscopy study of neon assisted recombination of H3+ ions with electrons

•The third-body assisted recombination of H3+ ions with electrons in ambient neon gas is studied using combination of simultaneous Cavity Ring-Down spectroscopy and electron number density measurements.•Electron - ion recombination rate coefficients can be obtained even at conditions when the studied ions are not dominant in plasma.•The Einstein A coefficient for second overtone transition of H3+ 3v21(2,0)←0v20(1,0) is determined.