The structure of microsolvated benzene derivatives and the role of aromatic substituents.

In this paper we report on the application of infrared/photoinduced Rydberg ionization (IR/PIRI) and IR-photodissociation spectroscopy to investigate the CH, NH or OH stretching vibrations of indole+ and the indole(H2O)1+ cluster cation. All vibrational frequencies of indole+ and indole(H2O)1+ are compared with the values obtained from ab initio calculations. In the case of the indole+ cation the NH vibration is observed. This is the first observation of a NH vibration in a bare cation. For indole(H2O)1+ a hydrogen-bonded structure with a nearly linear hydrogen bond can be derived both from ab initio calculations and the IR-spectra. By applying the state selective IR/PIRI spectroscopy to indole(H2O)1+, no vibrational couplings between the intermolecular O–H⋯N stretching vibration and the intramolecular OH stretching modes of the water moiety are observed. In the IR-photodissociation spectra of indole(H2O)1+ the NH, OH, and CH stretching vibrations as well as overtones of bending modes are observed. In agr...

Ultraviolet/infrared-double resonance spectroscopy and ab initio calculations on the indole + and indole(H2O)1 + cations

A new infrared spectroscopic technique for jet-cooled molecular cations is applied to observe intramolecular hydrogen bonds in substituted phenol ions. Vibrational transitions of an ion core of high Rydberg states are measured by detecting molecular ions prepared through vibrational autoionization. The observed infrared spectra practically provide vibrational frequencies of the corresponding bare molecular ion. The OH stretching vibrations of ortho-, meta-, and para-isomers of fluorophenol and methoxyphenol cations are observed. The OH stretching vibrational frequency of the ortho-isomer shows a characteristic redshift due to the intramolecular hydrogen bond. The redshift increases with ionization, indicating a significant enhancement of the intramolecular hydrogen bond strength.

Autoionization-detected infrared spectroscopy of intramolecular hydrogen bonds in aromatic cations. I. Principle and application to fluorophenol and methoxyphenol

Vibrational spectroscopic evidence of unconventional hydrogen bonds

The vibrational frequencies of the N−H stretching modes of aniline and diethylamine (DEA), after forming a strong H-bonded complex, are measured with infrared depletion spectroscopy that uses cluster-size-selective REMPI time-of-flight mass spectrometry. Three strong infrared absorption features observed at 3294, 3369, and 3473 cm-1 are assigned to the NH stretching vibration of DEA and H-bonded and free N−H stretching vibrations of aniline, respectively, in the 1:1 aniline−DEA complex. The spectral broadening observed for the free and H-bonded N−H stretching modes of aniline indicates mode-specific vibrational energy dynamics. Although the narrow bandwidth (≈4 cm-1) of the N−H stretch at 3473 cm-1 incorporates all of the common broadening mechanisms including intramolecular vibrational relaxation (IVR), the broader (≈13 cm-1) absorption feature at 3369 cm-1 suggests vibrational predissociation/IVR of the H-bonded complex, with a subpicosecond lifetime. The red-shifts of the N−H stretching vibrations of a...

Infrared Depletion Spectroscopy of the Hydrogen-Bonded Aniline−Diethylamine (C6H5-NH2···NHC4H10) Complex Produced in Supersonic Jet

Infrared depletion spectroscopy of the aniline-H2O+ cluster cation

The vibrational spectra of the aniline−pyrrole complex and the corresponding complex cation have been measured in the region of the NH stretching vibration using a mass-selective IR−UV double-resonance technique. In the spectrum of the neutral complex, there are three absorption bands at 3393, 3464, and 3496 cm-1, which have been assigned to the symmetric and antisymmetric stretching vibrations of the aniline NH2 group and the NH stretching vibration of pyrrole, respectively. The positions of the first two bands are close to those found in the aniline dimer and aniline−benzene complexes, suggesting that the neutral aniline−pyrrole complex has a similar parallel configuration. In the spectrum of the complex cation, three absorption bands have been observed at 3293, 3435, and 3498 cm-1. In this case, the first two bands appeared at the same positions as those of the aniline−benzene cation, which indicates that there is a hydrogen bond between one of the NH bonds of the aniline cation and the π-electron syst...

Koya Kawamata

Papers

Infrared depletion spectroscopy of the aniline-H2O+ cluster cation

Investigation of the N-H Stretching Vibrations of the Aniline-Pyrrole Binary Complex and Its Cation by Infrared Depletion Spectroscopy