45eV

45 eV (eighty‑five electronvolts) is a unit of energy equal to 45 times the elementary charge times one volt. It is commonly used in atomic, molecular, and solid‑state physics to describe the energy of photons, electrons, or ions that interact with matter. In the vacuum ultraviolet (VUV) and soft X‑ray regions, 45 eV corresponds to a wavelength of about 27.6 nanometers. This energy is sufficient to ionize helium atoms, to promote electrons from inner valence shells in heavier elements, and to excite certain electronic transitions in molecules and solids.

In photoelectron spectroscopy, beams of electrons with an energy near 45 eV are routinely employed because they provide a good balance between surface sensitivity and kinetic energy of the emitted electrons. The energy also lies within the range of many laboratory‐generated laser pulses and synchrotron radiation sources, enabling precise studies of electron dynamics on femtosecond timescales. Because 45 eV is above the ionization threshold for many light atoms, it is used to investigate radiation damage in biological samples and to monitor the formation of plasmas in high‑energy density experiments.

The value is also relevant in astrophysics, where processes such as the photoionization of interstellar gas by far‑ultraviolet starlight often involve photons with energies around 45 eV. In these environments, absorption by elements like carbon and nitrogen illustrates the importance of this energy range for the chemistry and cooling of the intergalactic medium.