## 1 Introduction
Regarding the species and interaction modes appearing in the TPPE method are as follows: (a) The key functional group: -OH group adsorbed on the metal surface and its polarity; (b) the electron density of the oxygen of -OH group, which depends on the negative electric potential and the intensity of irradiated light; (c) the orientation of adsorbate molecules due to the acid-base interaction in the adsorption on the -OH group; (d) the formation of electric dipoles between the -OH group and adsorbate molecules; (e) the change in the components of O1s spectra before and after the TPPE measurement. The dependence of TPPE on temperature and environment is quantified using PE stimulation spectra [26]. The following data and its relationship to the properties of the adsorbate molecules are obtained: (a) the total count of emitted electrons in the incident light wavelength scan (PE total count, \(N_{\rm T}\)), which may correspond to the transport distance of electrons released from the base metal. (b) The photothreshold representing the minimum photon energies needed to remove an electron from the surface of a material. But in this study, the values were not estimated. (c) The activation energies of \(N_{\rm T}\) for all Cu samples were obtained from an Arrhenius-type equation of \(N_{\rm T}=A_{0\rm NT}\) exp (\(-\Delta E/kT\)), where \(A_{0\rm NT}\) indicates the pre-exponential factor, \(k\) is the Boltzmann factor, and \(T\) is Kelvin. This expression was applied to \(N_{\rm T}\) values in the temperature increase and subsequent temperature decrease processes. (d) The relation of activation energies of \(\Delta E_{\rm Up1}\) (Up1 indicates the first temperature increase process) to [PERSON]'s acceptor number (\(AN\)), representingbasicity, and the reciprocal of dielectric constant (\(\epsilon/\epsilon_{0}\)) of the used liquids is examined. Regarding contact killing of viruses by metals, the action of electrons accumulated in the neighborhood of the reaction site is considered to be most essential according to Ref. [3], because of the increase in the reducibility of the metal. As the electron emission mechanism will be described in detail later, electrons in the base metal are captured by hydroxyl group radicals adsorbed at the surface, and then, Auger emission occurs, giving rise to a PE stimulation spectrum. \(\Delta E\) is considered to correspond to the trap depth of the hydroxyl group radical to attract electrons from the base metal. Further, we are interested in the relation of \(AN\) to \(1/(\epsilon/\epsilon_{0})\) of the liquids. As shown later it was found that the \(1/(\epsilon/\epsilon_{0})\) decreases with increasing \(AN\) for the liquids. The dependence of \(\Delta E\) on \(1/(\epsilon/\epsilon_{0})\) is also clarified for the liquids. The relation of TPPE to the XPS results is featured as follows: (a) Two components of O1s spectra, -OH (hydroxyl group) and O\({}^{2-}\) (oxide), are of great importance. (b) The increase in \(N_{\rm T}\) in PE stimulation spectra is confirmed to be strongly related to the increase in the intensity of -OH before the TPPE measurement. After the TPPE measurement, only the O\({}^{2-}\) component appears and the \(N_{\rm T}\) disappears. Although the detailed mechanism of the -OH group adsorbed at the surface is not clear, it is considered that it has the character of a radical, with the ability to attract electrons by tunnelling from the base metal, followed by Auger emission. The PE stimulation spectra appear as a result of the Auger emission. The ability of the hydroxyl group radical to attract electrons is influenced by the acid-base interaction between the -OH group and the liquids adsorbed around the -OH group, producing different \(\Delta E\)s.