Benchmarking quantum methods with experimental data: exploringrotational spectroscopy of water and alcohol complexes
Melandri, S.,1* Maris, A.,2 Evangelisti, L.,2 Lv, D.,2 Song, W.2*presenter
1sonia.melandri@unibo.it, University of Bologna, Italy
2University of Bologna, Italy
As is widely recognized, the environment within living organisms is intricate and dynamic,
wherein water serves as the foundation for numerous interactions among biomolecules. The
way molecules dissolve can significantly affect these important processes. Conformational
alterations during the dissolution process have the potential to influence the activity andbioavailability of molecules. 1
The study of small clusters in the gas phase offers a unique opportunity to characterize bothexperimentally and theoretically models of the molecular interactions which occur in bulk watersolutions. 2,3 The conformational space of such systems is generally shaped by non-covalentinteractions (NCIs) occurring within the molecule or with the surroundings. Moreover, theyusually possess a high number of low-energy conformations undergoing large amplitude
motions through shallow potential energy surfaces. For these reasons, the properties of such
systems are difficult to predict and are challenging for theoretical calculations.
High-resolution spectroscopy, in particular rotational spectroscopy, allows the deduction ofseveral molecular properties such as structural parameters (e.g. the moment of inertia, electric
dipole moments, centrifugal distortion and hyperfine coupling constants (i.e., nuclear
quadrupole, spin-rotation, and spin-spin quadrupole) which can be very well determined, both
numerically and also in terms of their physical description. The results of high-resolution
spectroscopy studies can be directly compared to the outcomes of theoretical calculations asregards the energy order of the stable configurations and their geometries. Consequently, they
offer valuable insights into the underlying driving forces governing interactions between waterand solute.
The rotational spectra of a few water and alcohol complexes of small organic molecules (e.g.
cysteamine and acrolein) will be presented. Very detailed structural information is obtained
from the observation of the normal and isotopic species which, integrated with the results ofquantum chemical calculations yielded valuable data for the determination of rs and r0. In
addition, our studies also consider the impact of the weak interactions and large amplitudestructural averaging correction. The comprehensive analysis of intermolecular interactions,employing diverse methodologies, has provided a thorough and in-depth insight into thebehavior of the molecules in the complexes.
1

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2Richardson, J. O. et al. Concerted hydrogen-bond breaking by quantum tunneling in the water hexamer prism
Science 2016 351,1310-1313.
(2016).
3
Evangelisti, L.; Brendel, K.; Maeder, H.; Caminati, W. and Melandri, S. Rotational Spectroscopy Probes Water
Flipping by Full Fluorination of Benzene, Angew. Chem. Int. Ed. 2017, 56, 13699 –13703