The pyrrole-water complex: Multidimensional large amplitude dynamics and rotational spectra of its 13C isotopologues.

A graphical abstract is mandatory for this journal. It should summarize the contents of the article in a concise, pictorial form designed to capture the attention of a wide readership online. Authors must provide images that clearly represent the work described in the article. Graphical abstracts should be submitted as a separate file in the online submission system. Image size: please provide an image with a minimum of 531 × 1328 pixels (h × w) or proportionally more. The image should be readable at a size of 5 × 13 cm using a regular screen resolution of 96 dpi. Preferred file types: TIFF, EPS, PDF or MS Office files. You can view Example Graphical Abstracts on our information site. Authors can make use of Elsevier's Illustration Services to ensure the best presentation of their images also in accordance with all technical requirements. • Assign rotational spectra of the carbon-13 isotopologues of pyrrole-water. • Obtain a two-dimensional potential energy surface scan on water-center motions. • Establish the average ground state structure, water tunneling path, and barrier. • Identify a barrierless, water large amplitude motion. The rotational spectrum of pyrrole-water was investigated before (Tubergen et al., 1993) In this work, we have applied a recently developed semiempirical tight-binding quantum chemistry program and DFT calculations to identify possible low energy conformers of the pyrrole-water complex which feature σ- and π-type hydrogen-bonding interactions. Using a cavity-based and two chirped pulse Fourier transform microwave spectrometers, we have measured and assigned all monosubstituted 13C isotopologues of pyrrole-water in their natural abundances. The 14N nuclear quadrupole hyperfine splittings and water tunneling doublets of these rarer isotopologues have also been observed and analyzed. Furthermore, we have carried out potential energy surface scans along possible paths of water large amplitude motions and identified all four previously proposed pyrrole-water geometries and correlated them to one global minimum and three transition states. The theoretical investigation together with the additional 13C experimental data allow one to confidently identify the ground state geometry and also estimate the water tunneling barrier. [ABSTRACT FROM AUTHOR]