title: Communication: He-tagged vibrational spectra of the SarGlyH⁺ and H⁺(H₂O)(2,3) ions: quantifying tag effects in cryogenic ion vibrational predissociation (CIVP) spectroscopy.
abstract: To assess the degree to which more perturbative, but widely used "tag" species (Ar, H2, Ne) affect the intrinsic band patterns of the isolated ions, we describe the extension of mass-selective, cryogenic ion vibrational spectroscopy to the very weakly interacting helium complexes of three archetypal ions: the dipeptide SarGlyH(+) and the small protonated water clusters: H(+)(H2O)(2,3), including the H5O2(+) "Zundel" ion. He adducts were generated in a 4.5 K octopole ion trap interfaced to a double-focusing, tandem time-of-flight photofragmentation mass spectrometer to record mass-selected vibrational predissociation spectra. The H2 tag-induced shift (relative to that by He) on the tag-bound NH stretch of the SarGlyH(+) spectrum is quite small (12 cm(-1)), while the effect on the floppy H5O2(+) ion is more dramatic (125 cm(-1)) in going from Ar (or H2) to Ne. The shifts from Ne to He, on the other hand, while quantitatively significant (maximum of 10 cm(-1)), display the same basic H5O2(+) band structure, indicating that the He-tagged H5O2(+) spectrum accurately represents the delocalized nature of the vibrational zero-point level. Interestingly, the He-tagged spectrum of H(+)(H2O)3 reveals the location of the non-bonded OH group on the central H3O(+) ion to fall between the collective non-bonded OH stretches on the flanking water molecules in a position typically associated with a neutral OH group.
authors.affiliation: Sterling Chemistry Laboratory, Yale University, 225 Prospect St., New Haven, Connecticut 06520, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Johnson
authors.affiliation: Sterling Chemistry Laboratory, Yale University, 225 Prospect St., New Haven, Connecticut 06520, USA.
authors.forename: Arron B
authors.initials: AB
authors.lastname: Wolk
authors.affiliation: Sterling Chemistry Laboratory, Yale University, 225 Prospect St., New Haven, Connecticut 06520, USA.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Fournier
authors.affiliation: Department of Chemistry and Biochemistry, Fairfield University, 1073 North Benson Rd., Fairfield, Connecticut 06824, USA.
authors.forename: Erin N
authors.initials: EN
authors.lastname: Sullivan
authors.affiliation: Sterling Chemistry Laboratory, Yale University, 225 Prospect St., New Haven, Connecticut 06520, USA.
authors.forename: Gary H
authors.initials: GH
authors.lastname: Weddle
authors.affiliation: Sterling Chemistry Laboratory, Yale University, 225 Prospect St., New Haven, Connecticut 06520, USA.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Johnson