The van der Waals vibrations of aniline–(argon)2 in the S1 electronic state

Abstract

Vibrational structure associated with van der Waals modes of the aniline–(argon)2 complex has been observed in the region near the origin of the S1←S0 electronic transition of the complex using resonance enhanced, multiphoton ionization (REMPI) spectroscopy. The aniline–Ar2 spectrum in this region displays only a few discrete bands built on an intense electronic origin. The dominant vibrational band, associated principally with the symmetric van der Waals stretching motion of the two argon atoms against the aromatic frame, occurs at 38.5 cm−1 displacement relative to the 000 band, with weaker transitions at 15 and 30 cm−1 displacement. A simple model for the van der Waals vibrations of aromatics bound to one and two rare gas atoms is developed and allows allow us to explain the aniline–Ar2 spectrum, using van der Waals bond parameters determined from the previously measured An–Ar1 spectrum. The agreement between the predicted and observed aniline–Ar2 spectrum confirms the view that van der Waals stretching vibrations are coupled anharmonically to near resonant bending vibrations in aniline–Ar1 and aniline–Ar2.

Mass analyzed threshold ionization spectra of phenol⋯Ar2: ionization energy and cation intermolecular vibrational frequencies

“…Previous examples of A (+) Á Á ÁAr n clusters with aromatic molecules include A = benzonitrile, 2,3 fluorobenzene, 4,5 and aniline. [6][7][8][9][10] Phenol is another fundamental mono-substituted benzene molecule with an electron donor group (OH) and two principle binding sites for neutral ligands. One interaction can be established with the substituent by the formation of a hydrogen bond to the OH group and the other binding motif corresponds to a van der Waals interaction with the aromatic p-electron system.…”

Intermolecular vibrations of fluorobenzene-Ar up to 130 cm−1 in the ground electronic state

“…Bieske, Rainbird, and Knight observed the S 1 van der Waals modes of aniline-Ar 2 (Ref. 15) and, assuming that the second Ar occupies an equivalent position to the first, related the observed trimer frequencies to those of the aniline-Ar dimer. Subsequently, Maxton et al reported intermolecular vibrations for a number of complexes in S 0 using Raman spectroscopy, including benzene-Ar 2 and fluorene-Ar 2 (Ref.…”

“…22,23 The formulae provided by Bieske et al allow the six FBAr 2 (1|1) intermolecular vibrational frequencies to be calculated from the three FB-Ar intermolecular frequencies and various constants associated with the complex. 15 (The six FBAr 2 (1|1) intermolecular modes are the symmetric and asymmetric motions associated with the long axis bend, short axis bend, and the stretch -see Table IV.) The formulae for the trimer (1|1) frequencies in terms of the FB-Ar dimer frequencies are of the general form:…”

“…15 The formulae are of the general form: Table IV. These formulae allow the interactions between the various stretch and bend levels in the trimer to be deduced from those in the dimer and vice versa.…”

“…The interest in this trimer complex derives from the formulae relating its vibrational frequencies and anharmonic coupling matrix elements to those of the FB-Ar dimer. 15 An analysis of the trimer spectrum provides both a test of these formula and an opportunity to extract otherwise unobserved dimer coupling strengths.…”