The electron affinity of the lutetium atom (element 71) was measured using the technique of photoelectron spectroscopy with an infrared laser (the essay on p. 310 describes this instrumental method, using X rays). In this experiment, a beam of lutetium negative ions, Lu–, was prepared and irradiated with a laser beam having a wavelength at 1064 nm. The energy supplied by a photon in this laser beam removes an electron from a negative ion, leaving the neutral atom. The energy needed to remove the electron from the negative ion to give the neutral atom (both in their ground states) is the electron affinity of lutetium. Any excess energy of the photon shows up as kinetic energy of the emitted electron. If the emitted electron in this experiment has a kinetic energy of 0.825 eV, what is the electron affinity of lutetium?
