Electronic Spectra of Protonated Benzaldehyde Clusters with Ar and N2: Effect of ππ* Excitation on the Intermolecular Potential

Electronic spectra of the S₁←S₀ transition of dimers of protonated benzaldehyde (BZH⁺) with Ar and N₂ are recorded by resonance-enhanced photodissociation in a tandem mass spectrometer. The S₁ origins observed are shifted to higher frequency upon complexation with Ar (ΔS₁ = 300 cm⁻¹) and N₂ (ΔS₁ = 628 cm⁻¹). Ab initio calculations at the CC2/aug-cc-pVDZ level suggest an assignment to H-bonded dimers of L = Ar and N₂ binding to the cis isomer of O-protonated BZH⁺, yielding values of ΔS₁ = 242 and 588 cm⁻¹ for cis-BZH⁺-L(H). Electronic ππ* excitation results in a substantial increase of the proton affinity of BZH⁺, which in turn destabilizes the intermolecular H-bonds to the inert ligands by 35%. The drastic effects of electronic ππ* excitation on the geometric and electronic structure as well as the strength and anisotropy of the intermolecular potential (H-bonding and π-bonding) are investigated.

Electronic Spectra of Protonated Benzaldehyde Clusters with Ar and N2: Effect of ππ* Excitation on the Intermolecular Potential. Alexander Patzer, Max Zimmermann, Ivan Alata, Christophe Jouvet, and Otto Dopfer. The Journal of Physical Chemistry A 2010 114 (48), 12600-12604