UV photoelectron spectroscopy (UPS) 

https://doi.org/10.1351/goldbook.U06583
Sources:
Orange Book, 2nd ed., p. 250 [Terms] [Book]
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2282 [Terms] [Paper]