Fragmentation Energetics of the Phenol⁺···Ar₃ Cation Cluster

Abstract

The various dissociation thresholds of phenol(+)···Ar(3) complexes for the consecutive loss of all three Ar ligands were measured in a molecular beam using resonant photoionization efficiency and mass analyzed threshold ionization spectroscopy via excitation of the first excited singlet state (S(1)). The adiabatic ionization energy is derived as 68077 ± 15 cm(-1). The analysis of the dissociation thresholds demonstrate that all three Ar ligands in the neutral phenol···Ar(3) tetramer are attached to the aromatic ring via π-bonding, denoted phenol···Ar(3)(3π). The value of the dissociation threshold for the loss of one Ar ligand from phenol(+)···Ar(3)(3π), ∼190 cm(-1), is significantly lower than the binding energy measured for the π-bonded Ar ligand in the phenol(+)···Ar(π) dimer, D(0) = 535 ± 3 cm(-1). This difference is rationalized by an ionization-induced π → H isomerization process occurring prior to dissociation, that is, one Ar atom in phenol(+)···Ar(3)(3π) moves to the OH binding site, leading to a structure with one H-bonded and 2 π-bonded ligands, denoted phenol(+)···Ar(3)(H/2π). The dissociation thresholds for the loss of two and three Ar atoms are also reported as 860 and 1730 cm(-1). From these values, the binding energy of the H-bound Ar atom can be estimated as 870 cm(-1).

Mass analyzed threshold ionization detected infrared spectroscopy: isomerization activity of the phenol–Ar cluster near the ionization threshold

“…[19][20][21][22][26][27][28] Tunable UV exc/ion laser pulses are generated by frequency doubling of outputs of two Nd:YAGpumped dye lasers (Radiant Dyes: Narrow scan, Continuum: Surelite 10). Tunable IR laser radiation is obtained from the idler output of an IR optical parametric oscillator (LaserVision).…”

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

“…37 Photoionisation efficiency (PIE) and photofragmentation studies of the n = 3 complex demonstrate that all Ar ligands are p-bonded in the isomer responsible for the intense S 1 origin at DS 1 = +23 cm À1 . 41 Hole-burning spectra reveal that all intense bands in these spectra are due to intermolecular structure of this isomer. 31 The interpretation of its geometry has, however, been conflicting so far.…”

“…13 In addition, the results will provide clues about the PhOH + -Ar m product isomers (m r n), which are experimentally observed upon ionisation of the neutral PhOH-Ar n precursors after the isomerisation and fragmentation processes. 6,32,37,41,46 …”

“…3a). 41 Again, there are several less stable (30)-type isomers, which can be obtained by internal rotation of the planar Ar 3 triangle above the aromatic plane. These are, however, less stable and not considered further because they are not detected experimentally.…”

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

“…In contrast, the corresponding A + -L dimer cations usually prefer H-bonds with the acidic functional group(s) due to additional charge-induced interactions arising from the excess charge. 9,13 This ionization-induced p -H switch in the preferred A (+) -L binding motif has recently been established via the combination of IR spectroscopy and quantum chemical calculations for a variety of acidic aromatic molecules interacting with rare gas (Rg) atoms, CH 4 , and N 2 , 9 including (substituted) phenols, [13][14][15][16][17][18][19][20][21][22] naphthol, 23 aniline, [24][25][26] aminobenzonitrile, 27,28 imidazole, 29,30 indole, 31 and tryptamine. 32 In some of these clusters, this ionization-induced p -H switch triggers an intermolecular isomerization reaction upon photoionization, which occurs on the picosecond timescale [33][34][35] and is usually inferred from IR spectra recorded before and after ionization using nanosecond laser systems.…”