Time-resolved photoelectron spectroscopy of bulk liquids at ultra-low kinetic energy

► This is the first realization of time-resolved photoelectron spectroscopy of bulk liquid, in which bulk means the inside of the liquid and not the surface. ► This bulk-sensitivity was achieved by observing ultra-low photoelectron kinetic energy (ULKE). The inelastic mean free path of an electron is greatly extended at ULKE, and this is essential for photoelectron spectroscopy of liquid. As far as we notice, TR-PES-ULKE has never been demonstrated. ► The technical problem of the streaming potential is reduced by optimization of salt concentration, and reliable calibration was demonstrated by measuring photoelectron kinetic energy of gas-phase species above the liquid surface. This calibration procedure is presented for the first time. ► Detailed analysis of the photoelectron signal intensity and spectral shift is presented for the first time.