Mass spectrometric study of O, O$_{\mathrm{2}}(a^{\mathrm{1}}\Delta _{\mathrm{g}})$ and O$_{\mathrm{3}}$ in time-modulated RF driven atmospheric pressure plasma jets*

A molecular beam mass spectrometer (MBMS) was established to measure fluxes of neutral and ionic species from atmospheric pressure plasma at a substrate. In this work, we report the first measurements of absolute densities of O$_{\mathrm{2}}(a^{\mathrm{1}}\Delta_{\mathrm{g}})$ in an atmospheric pressure plasma jet (APPJ) by MBMS. The ability to measure spatial profiles of O$_{\mathrm{2}}(a^{\mathrm{1}}\Delta _{\mathrm{g}})$ impinging on a substrate in the effluent of the APPJ is a key advantage of the MBMS over previously reported optical methods. The measured large O$_{\mathrm{2}}(a^{\mathrm{1}}\Delta_{\mathrm{g}})$ densities in the APPJ effluent, up to one order of magnitude higher than the O density, underline the potential importance of O$_{\mathrm{2}}(a^{\mathrm{1}}\Delta_{\mathrm{g}})$ in many applications. In addition, we also investigate the change of species fluxes impinging on a dielectric substrate for touching and non-touching conditions by equipping the MBMS with a dielectric sampling plate. Spatially resolved measurements of neutral and ionic species in an He$+$1{\%} O$_{\mathrm{2}}$ RF-driven APPJ are reported. The spatially resolved distribution of O, O$_{\mathrm{2}}(a^{\mathrm{1}}\Delta_{\mathrm{g}})$ and O$_{\mathrm{3\thinspace }}$is dominated by convection and, remarkably shows minimum differences between touching and non-touching conditions.