The correct identification of all gases released during hybrid perovskite degradation is of great significance to develop strategies to extend the lifespan of any device based on this semiconductor. CH3X (X = Br/I) is a released degradation gas/low boiling point liquid arising from methylammonium (MA+) based perovskites, which has been largely overlooked in the literature focusing on stability of perovskite solar cells. Herein, we present an unambiguous identification of CH3I release using microwave (rotational) spectroscopy. An experimental back-reaction test demonstrates that the well-known CH3NH2/HX degradation route may not be the ultimate degradation pathway of MAPbX3 in thermodynamic closed systems. Meanwhile, the CH3X/NH3 route cannot back-react selectively to MAX formation as occurred for the former back-reaction. Metadynamics calculations uncover the X halide effect on energy barriers for both degradation reactions showing a better stability of Br based perovskite ascribed to two aspects: (i) lower Brönsted–Lowry acidity of HBr compared to HI and (ii) higher nucleophilic character of CH3NH2 compared to NH3. The latter property makes CH3NH2 molecules stay preferentially attached on the electrophilic perovskite surface (Pb2+) during the dynamic simulation instead of being detached as observed for the NH3 molecule.

Modern structural studies of biologically relevant molecules require an exhaustive interplay between experiment and theory. In this work, we present two examples where a poor choice of the theoretical method led to a misinterpretation of experimental results. We do that by performing a rotational spectroscopy study on two large and flexible biomolecules: methyl jasmonate and zingerone. The results show the enormous potential of rotational spectroscopy as a benchmark to evaluate the performance of theoretical methods.

The conformational landscapes of β-ionone and two mutants (α-ionone and β-damascone) have been analyzed by means of state-of-the-art rotational spectroscopy and quantum-chemical calculations. The experiments performed at high resolution and sensitivity have provided a deep insight into their conformational spaces, assigning more than 8000 transitions corresponding to the rotational structures of 54 different species (3 isomers, 14 conformers, and 40 isotopologues). Methyl internal rotation dynamics were also observed and analyzed. The work proved the great flexibility of β-ionone due to its flatter potential energy surface. This feature confers on β-ionone a wider ability to interconvert between conformers with rather similar energies with respect to its mutants, allowing the retinal ligand to better adapt inside the binding pocket.

The investigation of an isolated ribofuranose unit in the gas phase reveals the intrinsic conformational landscape of the biologically active sugar form. We report the rotational spectra of two conformers of methyl β-d-ribofuranoside in a supersonic jet expansion. Both conformers adopt a near twisted ((3)T2) ring conformation with the methoxy and hydroxymethyl substituents involved in various intramolecular hydrogen bonds.