text: In peptide bonds, one of these phenomena produces a well-characterized signal designated "NV1."
full_question: In peptide bonds, one of these phenomena produces a well-characterized signal designated "NV1." The intensity of these phenomena can be increased by d-p mixing or vibronic coupling. CT complexes can undergo LMCT or MLCT examples of these phenomena. In two types of diagrams depicting these phenomena, lines become curved due to the non-crossing rule. In one set of diagrams depicting the energies of these phenomena, both axes are normalized by the Racah parameter. Examples of this kind of process include intersystem crossing, where a difference in spin multiplicity allows this kind of process to occur in a non-radiative fashion. Sandwiching the electric dipole operator between the initial and final state wavefunctions for this process can be used to derive the fact that the azimuthal quantum number must change by plus or minus one, or this process is said to be "forbidden" according to a selection rule. For 10 points, name this process by which a molecule's electrons change energy levels.
first_sentence: In peptide bonds, one of these phenomena produces a well-characterized signal designated "NV1."
raw_answer: molecular electronic transitions [or electron excitation; or word forms; or light or energy absorption; or photon emission]