Ultraviolet photodissociation action spectroscopy of the N-pyridinium cation

Abstract

The S1←S0 electronic transition of the N-pyridinium ion (C5H5NH+) is investigated using ultraviolet photodissociation (PD) spectroscopy of the bare ion and also the N2-tagged complex. Gas-phase Npyridinium ions photodissociate by the loss of molecular hydrogen (H2) in the photon energy range 37 000-45 000 cm−1 with structurally diagnostic ion-molecule reactions identifying the 2-pyridinylium ion as the exclusive co-product. The photodissociation action spectra reveal vibronic details that, with the aid of electronic structure calculations, support the proposal that dissociation occurs through an intramolecular rearrangement on the ground electronic state following internal conversion. Quantum chemical calculations are used to analyze the measured spectra. Most of the vibronic features are attributed to progressions of totally symmetric ring deformation modes and out-of-plane modes active in the isomerization of the planar excited state towards the non-planar excited state global minimum. The S 1 ← S 0 electronic transition of the N -pyridinium ion (C 5 H 5 NH + ) is investigated using ultraviolet photodissociation spectroscopy of the bare ion and also the N 2 -tagged complex. Gas-phase N -pyridinium ions photodissociate by the loss of molecular hydrogen (H 2 ) in the photon energy range 37 000 -45 000 cm

Vibronic spectra of protonated hydroxypyridines: contributions of prefulvenic and planar structures

“…These optimized structures are true minima of the PES without imaginary frequency. These two adiabatic structures closely resemble the N-pyridinium excited state structure calculated at the DFT/CAM-B3LYP/aug-cc-pVDZ by Hansen et al 24 , although the nitrogen pyramidalization is less pronounced in the present case. In pyridinium, the barrier height to planarity is calculated at 2000 cm -1 , while in 2-and 3-HPH + , CC2/aug-cc-pVDZ calculations predict a very small barrier of about 100 cm -1 (see Table 2).…”

“…The simplest protonated aromatic molecule, benzene, and aromatic nitrogen heterocycle, pyridine, have been characterized at medium resolution only very recently. 23,24 The electronic spectrum of protonated benzene is structure-less, which is in agreement with the large geometrical changes and the fast dynamic toward internal conversion predicted by ab-initio calculations. 25 Concerning protonated pyridine, the spectra recorded in the photon energy range 37000 -45000 cm -1 reveal a broad electronic band exhibiting vibronic resolved structure.…”

Ultraviolet photodissociation action spectroscopy of gas-phase protonated quinoline and isoquinoline cations

“…shorter wavelengths) and is raised o↵ the baseline with a broad envelope. 47 The intense broad and unfeatured band centred around 32 000 cm 1 is not predicted by this simulation. Table 1 lists a second electronic transition, to S 2 , with a vertical excitation energy approximately 3500 cm 1 higher than that to S 1 .…”

Electronic Spectroscopy of Protonated 1‐Aminopyrene in a Cold Ion Trap

“…A comparison of the calculated vibronic spectrum (S 1 ) with the experimental spectrum is shown in the Supporting Information, Figure SI.2. Compared to other protonated molecules, the Franck–Condon simulation performed relatively poorly at reproducing the experimental band intensities, although the frequencies were rather well‐reproduced (see the Supporting Information, Table SI.1). In particular, in the Franck–Condon simulation, the 0–0 band was by far the most intense, whereas, in the experimental spectrum, the other bands had comparable intensities for this first excited state.…”