Photoionization-induced large-amplitude pendular motion in phenol(+)-Kr

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The dynamics of the intermolecular motion of the phenol+–Kr cation generated by photoionization of the neutral π-structure is probed by picosecond time-resolved infrared spectroscopy. The spectrum at zero delay displays only the free OH stretch band of the π-structure. The appearance of the hydrogen-bonded OH stretch band of the H-structure after a few ps is due to ionization-induced π → H site switching. Spectra at long delay (>20 ns) show that the Kr atom delocalizes from one π-site of the aromatic ring to the opposite π-site via the OH-site, like a pendular motion in the classical picture

Ionization-induced pi -> H site switching dynamics in phenol-Ar-3

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Electronic excitation spectra of the S1 ← S0 transition obtained by resonance-enhanced two-photon ionization (REMPI) are analysed for phenol–Arn (PhOH–Arn) clusters with n ≤ 4. An additivity rule has been established for the S1 origin shifts upon sequential complexation at various π binding sites, which has allowed for the identification of two less stable isomers not recognized previously, namely the (2/0) isomer for n = 2 and the (2/1) isomer for n = 3. Infrared (IR) spectra of neutral PhOH–Arn and cationic PhOH+–Arnclusters are recorded in the vicinity of the OH and CH stretch fundamentals (νOH, νCH) in their S0 and D0 ground electronic states using IR ion dip spectroscopy. The small monotonic spectral redshifts ΔνOH of about −1 cm−1 per Ar atom observed for neutral PhOH–Arn are consistent with π-bonded ligands. In contrast, the IR spectra of the PhOH+–Arn cations generated by resonant photoionization of the neutral precursor display the signature of H-bonded isomers, suggesting that ionization triggers an isomerization reaction, in which one of the π-bonded Ar ligands moves to the more attractive OH site. The dynamics of this isomerization reaction is probed for PhOH+–Ar3 by picosecond time-resolved IR spectroscopy. Ionization of the (3/0) isomer of PhOH+–Ar3(3π) with three π-bonded Ar ligands on the same side of the aromatic ring induces a π → H switching reaction toward the PhOH+–Ar3(H/2π) isomer with a time constant faster than 3 ps. Fast intracluster vibrational energy redistribution prevents any H → π back reaction

Structural motifs of 2-(2-fluoro-phenyl)-ethylamine conformers

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Vibronic and vibrational spectra of 2-(2-fluoro-phenyl)-ethylamine (2-FPEA) conformers were measured in a molecular beam by resonant two-photon ionization (R2PI), ultraviolet-ultraviolet hole burning (UV-UV HB) spectroscopy, and ionization-loss stimulated Raman spectroscopy (ILSRS). The measured ILSR spectral signatures in the survey spectra of the amino group region and in the broad spectral range revealed the presence of five different conformers, which were confirmed by the HB spectra. The determination of the structures of the conformers of 2-FPEA was assisted by quantum chemical calculations of the torsional potential energy surface and of the scaled harmonic Raman spectra. Comparison of the measured ILSR spectra with the calculated Raman spectra allowed us to identify one gauche structure with the ethylamino side chain folded toward the fluorine atom, two gauche structures with the ethylamino side chain folded to the opposite side and two anti conformers with extended tails. The effect of fluorination on the spectra and on the stability and structures of these species is discussed

Unusual behavior in the first excited state lifetime of catechol

International audienceWe are presenting vibrationally selective pump-probe measurements of the first electronic excited-state (pp*) lifetime of jet-cooled neutral catechol (1,2-dihydroxybenzene). The lifetime of the 0-0 transition is very short (7 ps) as rationalized by the small pp*/psigma* gap calculated. However the lifetimes implying higher out-of-plane vibrational levels are longer (~11 ps). This emphasizes the role of the out-of-plane vibration in the pp*/psigma* coupling not only in its nature but also in the number of quant

Collision-assisted stripping for determination of microsolvation-dependent protonation sites in hydrated clusters by cryogenic ion trap infrared spectroscopy: the case of benzocaineH+(H2O)n

The protonation site of molecules can be varied by their surrounding environment. Gas-phase studies, including the popular techniques of infrared spectroscopy and ion mobility spectrometry, are a powerful tool for the determination of protonation sites in solvated clusters but often suffer from inherent limits for larger hydrated clusters. Here, we present collision-assisted stripping infrared (CAS-IR) spectroscopy as a new technique to overcome these problems and apply it in a proof-of-principle experiment to hydrated clusters of protonated benzocaine (H+BC), which shows protonation-site switching depending on the degree of hydration. The most stable protomer of H+BC in the gas phase (O-protonated) is interconverted into its most stable protomer in aqueous solution (N-protonated) upon hydration with three water molecules. CAS-IR spectroscopy enables us to unambiguously assign protonation sites and quantitatively determine the relative abundance of various protomers.TU Berlin, Open-Access-Mittel – 202

Ionization-induced pi -> H site-switching in phenol-CH4 complexes studied using IR dip spectroscopy

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.IR spectra of phenol–CH4 complexes generated in a supersonic expansion were measured before and after photoionization. The IR spectrum before ionization shows the free OH stretching vibration (νOH) and the structure of neutral phenol–CH4 in the electronic ground state (S0) is assigned to a π-bound geometry, in which the CH4 ligand is located above the phenol ring. The IR spectrum after ionization to the cationic ground state (D0) exhibits a red shifted νOH band assigned to a hydrogen-bonded cationic structure, in which the CH4 ligand binds to the phenolic OH group. In contrast to phenol–Ar/Kr, the observed ionization-induced π → H migration has unity yield for CH4. This difference is attributed to intracluster vibrational energy redistribution processes