The magnified infectious power of the SARS-CoV-2 virus compared to its precursor SARS-CoV is intimately linked to an enhanced ability in the mutated virus to find available hydrogen-bond sites in the host cells. This characteristic is acquired during virus evolution because of the selective pressure exerted at the molecular level. We pinpoint the specific residue (in the virus) to residue (in the cell) contacts during the initial recognition and binding and show that the viruscell interaction is mainly due to an extensive network of hydrogen bonds and to a large surface of noncovalent interactions. In addition to the formal quantum characterization of bonding interactions, computation of absorption spectra for the specific viruscell interacting residues yields significant shifts of Deltalambdamax =47 and 66 nm in the wavelength for maximum absorption in the complex with respect to the isolated host and virus, respectively.