Experimental ground-state combination differences of CH5

• Published in: Science (American Association for the Advancement of Science) Vol. 347; no. 6228; pp. 1346 - 1349
• Main Authors: Asvany, Oskar, Yamada, Koichi M. T., Brünken, Sandra, Potapov, Alexey, Schlemmer, Stephan
• Format: Journal Article
• Language: English
• Published: Washington American Association for the Advancement of Science 20.03.2015; The American Association for the Advancement of Science
• Subjects: Clusters; Grounds; Headways; Hydrogen; Hydrogen bonds; Methane; Molecular chemistry; Molecular structure; Order disorder; Quantum Mechanics; Spectra; Spectroscopy
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.aaa3304

Protonation of methane (CH4), a rather rigid molecule well described by quantum mechanics, produces CH5+, a prototypical floppy molecule that has eluded definitive spectroscopic description. Experimental measurement of high-resolution spectra of pure CH5+ samples poses a formidable challenge. By applying two types of action spectroscopy predicated on photoinduced reaction with CO2 and photoinhibition of helium cluster growth, we obtained low-temperature, high-resolution spectra of mass-selected CH5+. On the basis of the very high accuracy of the line positions, we determined a spectrum of combination differences. Analysis of this spectrum enabled derivation of equally accurate ground state–level schemes of the corresponding nuclear spin isomers of CH5+, as well as tentative quantum number assignment of this enfant terrible of molecular spectroscopy.