Electronic and vibrational spectra of protonated benzaldehyde-water clusters, [BZ-(H2O)n≤5]H+: evidence for ground-state proton transfer to solvent for n ≥ 3.

Vibrational and electronic photodissociation spectra of mass-selected protonated benzaldehyde-(water)n clusters, [BZ-(H2O)n]H(+) with n ≤ 5, are analyzed by quantum chemical calculations to determine the protonation site in the ground electronic state (S0) and ππ(*) excited state (S1) as a function of microhydration. IR spectra of [BZ-(H2O)n]H(+) with n ≤ 2 are consistent with BZH(+)-(H2O)n type structures, in which the excess proton is localized on benzaldehyde. IR spectra of clusters with n ≥ 3 are assigned to structures, in which the excess proton is located on the (H2O)n solvent moiety, BZ-(H2O)nH(+).

Microsolvation of the acetanilide cation (AA(+)) in a nonpolar solvent: IR spectra of AA(+)-L(n) clusters (L = He, Ar, N2; n ≤ 10).

Infrared photodissociation (IRPD) spectra of mass-selected cluster ions of acetanilide (N-phenylacetamide), AA(+)-Ln, with the ligands L = He (n = 1-2), Ar (n = 1-7), and N2 (n = 1-10) are recorded in the hydride stretch (amide A, νNH, νCH) and fingerprint (amide I-III) ranges of AA(+) in its (2)A'' ground electronic state. Cold AA(+)-Ln clusters are generated in an electron impact ion source, which predominantly produces the most stable isomer of a given cluster ion. Systematic vibrational frequency shifts of the N-H stretch fundamentals (νNH) provide detailed information about the sequential microsolvation process of AA(+) in a nonpolar (L = He and Ar) and quadrupolar (L = N2) solvent.

Solvent migration in microhydrated aromatic aggregates: ionization-induced site switching in the 4-aminobenzonitrile-water cluster.

The dependence of the preferred microhydration sites of 4-aminobenzonitrile (4ABN) on electronic excitation and ionization is determined through IR spectroscopy of its clusters with water (W) in a supersonic expansion and through quantum chemical calculations. IR spectra of neutral 4ABN and two isomers of its hydrogen-bonded (H-bonded) 4ABN-W complexes are obtained in the ground and first excited singlet states (S0, S1) through IR depletion spectroscopy associated with resonance-enhanced multiphoton ionization. Spectral analysis reveals that electronic excitation does not change the H-bonding motif of each isomer, that is, H2O binding either to the CN or the NH site of 4ABN, denoted as 4ABN-W(CN) and 4ABN-W(NH), respectively.

Experimental observation and quantum chemical characterization of the S1 ← S0 transition of protonated naphthalene-argon clusters.

We report on the photodissociation spectrum of protonated naphthalene(+)-argon complexes (NpH(+)-Ar) recorded by excitation into the first excited singlet electronic state. Unlike previous electronic spectra of the free molecule (NpH(+)), both the α and the β isomer could be observed for the Ar adducts. Detailed information on the S0 and S1 state of both isomers is provided by quantum chemical calculations.

Microsolvation of the 4-aminobenzonitrile cation (ABN+) in a nonpolar solvent: IR spectra of ABN(+)-L(n) (L=Ar and N2, n≤4).

IR photodissociation (IRPD) spectra of mass-selected cluster ions of 4-aminobenzonitrile (ABN(+)) with up to four Ar and N2 ligands are recorded over the spectral range of the N-H stretching vibrations (ν(s/a)) of ABN(+) in its (2)B1 ground electronic state. ABN(+)-L(n) clusters are produced in an electron impact cluster ion source, which predominantly generates the most stable isomer of a given cluster ion. Vibrational frequency shifts of ν(s/a) provide information about the sequential microsolvation process of ABN(+) in a nonpolar solvent.

Infrared spectrum and structure of the adamantane cation: direct evidence for Jahn-Teller distortion.

The fundamentals: the IR spectrum of the adamantane cation, C(10)H(16)(+), has been derived by resonant IR photodissociation of weakly bound C(10)H(16)(+)⋅L(n) clusters. The analysis of the IR spectrum provides the first spectroscopic characterization of this fundamental cycloalkane carbocation in the gas phase and direct evidence for the Jahn-Teller distortion in the (2)A(1) ground electronic state.

Structures and IR/UV spectra of neutral and ionic phenol-Ar(n) cluster isomers (n ≤ 4): competition between hydrogen bonding and stacking.

The structures, binding energies, and vibrational and electronic spectra of various isomers of neutral and ionic phenol-Ar(n) clusters with n ≤ 4, PhOH((+))-Ar(n), are characterized by quantum chemical calculations. The properties in the neutral and ionic ground electronic states (S(0), D(0)) are determined at the M06-2X/aug-cc-pVTZ level, whereas the S(1) excited state of the neutral species is investigated at the CC2/aug-cc-pVDZ level. The Ar complexation shifts calculated for the S(1) origin and the adiabatic ionisation potential, ΔS(1) and ΔIP, sensitively depend on the Ar positions and thus the sequence of filling the first Ar solvation shell.

Microhydration effects on the electronic spectra of protonated polycyclic aromatic hydrocarbons: [naphthalene-(H2O)(n = 1,2)]H+.

Vibrational and electronic spectra of protonated naphthalene (NaphH(+)) microsolvated by one and two water molecules were obtained by photofragmentation spectroscopy. The IR spectrum of the monohydrated species is consistent with a structure with the proton located on the aromatic molecule, NaphH(+)-H(2)O. Similar to isolated NaphH(+), the first electronic transition of NaphH(+)-H(2)O (S(1)) occurs in the visible range near 500 nm.

Electronic spectra of protonated benzaldehyde clusters with Ar and N2: effect of ππ* excitation on the intermolecular potential.

Electronic spectra of the S(1)←S(0) transition of dimers of protonated benzaldehyde (BZH(+)) with Ar and N(2) are recorded by resonance-enhanced photodissociation in a tandem mass spectrometer. The S(1) origins observed are shifted to higher frequency upon complexation with Ar (ΔS(1) = 300 cm(-1)) and N(2) (ΔS(1) = 628 cm(-1)). Ab initio calculations at the CC2/aug-cc-pVDZ level suggest an assignment to H-bonded dimers of L = Ar and N(2) binding to the cis isomer of O-protonated BZH(+), yielding values of ΔS(1) = 242 and 588 cm(-1) for cis-BZH(+)-L(H).

Infrared spectra and quantum chemical characterization of weakly bound clusters of the benzoyl cation with Ar and H(2)O.

Weakly-bound clusters of the closed-shell benzoyl cation (C(6)H(5)CO(+), PhCO(+)) with Ar and H(2)O are investigated by infrared (IR) spectroscopy, mass spectrometry, and quantum chemical calculations in order to characterize the interaction of a closed shell aromatic cation with a nonpolar and a polar ligand. PhCO(+)-L dimers are produced by electron ionization of benzaldehyde in a supersonic plasma expansion. IR photodissociation (IRPD) spectra of PhCO(+)-L with L = Ar and H(2)O are analyzed in the C-O, C-H, and O-H stretch ranges (2000-3900 cm(-1)).

IR spectra of protonated benzaldehyde clusters, C(7)H(7)O(+)-L(n) (L=Ar,N(2);n

Infrared photodissociation (IRPD) spectra of mass-selected protonated benzaldehyde (C(7)H(7)O(+),BZH(+)) and its weakly bound clusters with Ar and N(2) produced in an electron impact source are recorded in the C-H and O-H stretch ranges. The experimental results are supported by ab initio and density functional calculations. Analysis of the IRPD spectrum of the BZH(+) monomer is consistent with the presence of the cis and trans isomers of the oxonium ions, which is confirmed by the cluster spectra.