title: Microsolvation of the formanilide cation (FA+) in a nonpolar solvent: infrared spectra of FA(+)-Ln clusters (L = Ar, N2; n ≤ 8).
abstract: Infrared photodissociation (IRPD) spectra of cationic formanilide (N-phenylformamide) clusters, FA(+)-Ln, with L = Ar (n = 1-8) and N2 (n = 1-6), are recorded in the hydride stretch (amide A, νNH, νCH) and fingerprint (amide I-III) ranges to probe the preferred interaction motifs and the cluster growth. Cold FA(+)-Ln clusters are generated by electron ionization in a supersonic expansion, which generates predominantly the most stable cluster isomers. Size- and isomer-specific νNH frequencies unravel the microsolvation process of FA(+) in a nonpolar (L = Ar) and a quadrupolar (L = N2) solvent. The H-bound FA(+)-L dimer with L binding to the NH proton of the amide group is the most stable isomer, and further ligands are attached to the aromatic ring (π-stacking). Ionization changes the preferred binding motif from π-stacking to H-bonding in FA((+))-L. Quantum chemical calculations at the ωB97X-D/aug-cc-pVTZ level confirm the experimentally derived sequential cluster growth and the vibrational and isomer assignments. The calculated FA(+)-L binding energies of D0(H) = 594/1054 cm(-1) for H-bound and D0(π) = 459/604 cm(-1) for π-bound Ar/N2 ligands are consistent with the observed photofragmentation branching ratios. Ionization of FA results from removal of a bonding π-electron delocalized over the phenyl and amide moieties and thus weakens the N-H bond and strengthens the C-O bond.
authors.affiliation: Institut für Optik und Atomare Physik, Technische Universität Berlin , Hardenbergstrasse 36, 10623 Berlin, Germany.
authors.forename: Johanna
authors.initials: J
authors.lastname: Klyne
authors.forename: Matthias
authors.initials: M
authors.lastname: Schmies
authors.forename: Otto
authors.initials: O
authors.lastname: Dopfer
mesh_terms: D001128:Argon / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D003198:Computer Simulation; D005559:Formamides / Q000737:chemistry*; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry*; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry; D013055:Spectrophotometry, Infrared
chemical_list: D002412:Cations; D005559:Formamides; D012997:Solvents; C045976:N-phenylformamide; D001128:Argon; D009584:Nitrogen