The detailed analysis of the phase transition occurring in the metallic monatomic mercury layer (MMML) deposited electrolytically on the chemically inert carbon fiber is presented. The electrochemical equivalent (Q) of the MMML, which measures ≈ 420 μC cm^-2, denotes that the phase transition results in formation of a new two dimensional mercury phase with a compactly packed perfect quasi-crystallographic lattice. At fractional coverage of the carbon fiber by the Hg atoms close to the unity at room temperature there are reached the necessary conditions for the Bose-Einstein condensation of the MMML specified by de Broglie wavelength of the order of ∼3.34 × 10^-8 cm and by the weak Hg-Hg and Hg-carbon support interactions. The compactly packed perfect quasi-crystallographic lattice of the MMML and the high planar density of Hg atoms (1.31 × 10¹⁵ cm^-2) creates conditions for the Hg valence (6s²) electrons to form so called the superconducting 'Cooper pairs'. The dc biasing, trough an entrapped Cu atom connected to the power source, shows that at room temperature the 2D Hg phase possesses superconducting properties confirmed by the transport of the double charged quasi-particles-the quasi electron e∗ = -2 e during the positive bias, and the quasi-hole h∗ = +2 e during the negative bias. The superconducting properties at room temperature of the 2D mercury phase are a direct confirmation of the Einstein hypothesis that during BE condensation the added extra bosons collapse to the ground state. The opening of the superconductor energy gap, compiling 1.26 meV, stipulates a strong absorption by the 2D Hg phase of light in visible domain of the electromagnetic spectrum. The absorption of all incident on the MMML photons confirms that the valence electrons of all Hg atoms in the MMML are 'Cooper' paired. It is shown that the absorbed photon energy is converted to the electrical one in real time trough the non-adiabatic Landau-Zener collisional mechanism of energy transfer from the optically excited Hg atoms to the biased Cu atom.