title: Vibrational dynamics. Experimental ground-state combination differences of CH₅⁺.
abstract: 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.
authors: I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.
authors: Oskar
authors: O
authors: Asvany
authors: Environmental Molecular Science Group, EMTech, AIST Tsukuba West, Onogawa 16-1, Tsukuba, Ibaraki 305-8569, Japan.
authors: Koichi M T
authors: KM
authors: Yamada
authors: I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.
authors: Sandra
authors: S
authors: Brünken
authors: I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.
authors: Alexey
authors: A
authors: Potapov
authors: I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany. schlemmer@ph1.uni-koeln.de.
authors: Stephan
authors: S
authors: Schlemmer