Intermolecular dissociation energies of 1-naphthol·n-alkane complexes.

Richard Knochenmuss,Franziska Balmer,Charlotte Müller,Surajit Maity,Samuel Leutwyler

doi:10.1063/1.5034110

Abstract

Using the stimulated-emission-pumping/resonant 2-photon ionization (SEP-R2PI) method, we have determined accurate intermolecular dissociation energies D0 of supersonic jet-cooled intermolecular complexes of 1-naphthol (1NpOH) with alkanes, 1NpOH·S, with S = methane, ethane, propane, and n-butane. Experimentally, the smaller alkanes form a single minimum-energy structure, while 1-naphthol·n-butane forms three different isomers. The ground-state dissociation energies D0(S0) for the complexes with propane and n-butane (isomers A and B) were bracketed within ±0.5%, being 16.71 ± 0.08 kJ/mol for S = propane and 20.5 ± 0.1 kJ/mol for isomer A and 20.2 ± 0.1 kJ/mol for isomer B of n-butane. All 1NpOH·S complexes measured previously exhibit a clear dissociation threshold in their hot-band detected SEP-R2PI spectra, but weak SEP-R2PI bands are observed above the putative dissociation onset for the methane and ethane complexes. We attribute these bands to long-lived complexes that retain energy in rotation-type intermolecular vibrations, which couple only weakly to the dissociation coordinates. Accounting for this, we find dissociation energies of D0(S0) = 7.98 ± 0.55 kJ/mol (±7%) for S = methane and 14.5 ± 0.28 kJ/mol (±2%) for S = ethane. The D0 values increase by only 1% upon S0 → S1 excitation of 1-naphthol. The dispersion-corrected density functional theory methods B97-D3, B3LYP-D3, and ωB97X-D predict that the n-alkanes bind dispersively to the naphthalene "Face." The assignment of the complexes to Face structures is supported by the small spectral shifts of the S0 → S1 electronic origins, which range from +0.5 to -15 cm-1. Agreement with the calculated dissociation energies D0(S0) is quite uneven, the B97-D3 values agree within 5% for propane and n-butane, but differ by up to 20% for methane and ethane. The ωB97X-D method shows good agreement for methane and ethane but overestimates the D0(S0) values for the larger n-alkanes by up to 20%. The agreement of the B3LYP-D3 D0 values is intermediate between the other two methods.

Highlights

London dispersion forces arise from long-range electron correlation between atoms and molecules.1,2 These noncovalent interactions between atoms or molecules are always attractive and are present in all forms of condensed matter
Following the “pump” and “dump” steps, the vibrational predissociation of the hot 1-naphthol·S levels is detected by a third time-delayed laser by resonant two photon ionization (R2PI) at “hot” vibronic transitions that lie close to the 000 band of the state dissociation energies D0 (S0) → S1 transition
This triply resonant method is abbreviated as stimulated-emission pumping (SEP)-R2PI;13,31–36,38,42 a scheme is shown in Fig. S1 of the supplementary material

Summary

Introduction

London dispersion forces arise from long-range electron correlation between atoms and molecules. These noncovalent interactions between atoms or molecules are always attractive and are present in all forms of condensed matter. London dispersion forces arise from long-range electron correlation between atoms and molecules.. London dispersion forces arise from long-range electron correlation between atoms and molecules.1,2 These noncovalent interactions between atoms or molecules are always attractive and are present in all forms of condensed matter. They contribute importantly to the structures and lattice energies of molecular solids and are involved in phenomena such as enzyme-substrate binding, drug-substrate interactions, and protein folding, so they are of great importance in fields ranging from solid-state physics to chemical biology.. London dispersion energies between two closed-shell atoms are fairly weak, they increase with the number of atoms in molecular systems, so their additive nature is underestimated. Calculations of dispersive interactions between polyatomic molecules are still remarkably challenging for wave function methods, since high-level correlated methods and large diffuse basis sets are necessary to accurately capture the intermolecular correlation energy. In density-functional theory (DFT), the introduction of dispersion-corrected functionals has provided a major advance. the parametrization of the dispersion terms employed in DFT-D methods has mainly been based on calculations, and the databases used to benchmark DFT-D calculations of dispersively bound complexes are themselves mostly based on calculations. Of the noncovalent interaction energies in the GMTKN30 database, only six dissociation energies are based on experiment. It is important to gather

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Discussion

Conclusion