Measuring Intermolecular Binding Energies by Laser Spectroscopy

作者：Knochenmuss Richard; Maity Surajit; Feraud Geraldine; Leutwyler Samuel^*

来源：Chimia, 2017, 71(1-2): 7-12.

DOI：10.2533/chimia.2017.7

• Dispersive interactions
• Hydrogen bonding
• Intermolecular interactions
• Stimulated emission pumping

The ground-state dissociation energy, D-0(S-0), of isolated intermolecular complexes in the gas phase is a fundamental measure of the interaction strength between the molecules. We have developed a three-laser, triply resonant pump-dump-probe technique to measure dissociation energies of jet-cooled M center dot S complexes, where M is an aromatic chromophore and S is a closed-shell 'solvent' molecule. Stimulated emission pumping (SEP) via the S-0 <-> S-1 electronic transition is used to precisely 'warm' the complex by populating high vibrational levels v" of the S-o state. If the deposited energy E(v") is less than D-0(S-0), the complex remains intact, and is then mass- and isomer-selectively detected by resonant two-photon ionization (R2PI) with a third (probe) laser. If the pumped level is above D-0(S-0), the hot complex dissociates and the probe signal disappears. Combining the fluorescence or SEP spectrum of the cold complex with the SEP breakoff of the hot complex brackets D-0(S-0). The UV chromophores 1-naphthol and carbazole were employed; these bind either dispersively via the aromatic rings, or form a hydrogen bond via the -OH or -NH group. Dissociation energies have been measured for dispersively bound complexes with noble gases (Ne, Kr, Ar, Xe), diatomics (N-2, CO), alkanes (methane to n-butane), cycloalkanes (cyclopropane to cycloheptane), and unsaturated compounds (ethene, benzene). Hydrogen-bond dissociation energies have been measured for H2O, D2O, methanol, ethanol, ethers (oxirane, oxetane), NH3 and ND3.

• 出版日期2017