The chirality controlled conformational landscape of the trimer of propylene oxide (PO), a prototypical chiral molecule, was investigated using rotational spectroscopy and a range of theoretical tools for conformational searches and for evaluating vibrational contributions to effective structures. Two sets of homochiral (PO)₃ rotational transitions were assigned and the associated conformers identified with theoretical support. One set of heterochiral (PO)₃ transitions was assigned, but no structures generated by one of the latest, advanced conformational search codes could account for them. With the aid of a Python program, the carbon atom backbone and then the heterochiral (PO)₃ structure were generated using ¹³C isotopic data. Excellent agreement between theoretical and experimental rotational constants and relative dipole moment components of all three conformers was achieved, especially after applying vibrational corrections to the rotational constants.

The rotational spectrum of perillyl alcohol, a naturally occurring, chiral, dietary monoterpene, was investigated using a chirped pulse Fourier transform microwave spectrometer and a cavity-based Fourier transform microwave spectrometer. To aid the assignment of the dense chirped pulse spectrum obtained, extensive theoretical conformational searches were carried out. In one approach, several one and two-dimensional scans along three dihedral angles associated with the rotational motions of the –OH, –CH₂OH, and –C(CH₂)CH₃ groups were performed. These scans, combined with the equatorial and axial positions of the –C(CH₂)CH₃ group, resulted in 54 conformers. The same conformers were identified in the second approach where a semi-classical conformational search code was used. The relative stabilities of the conformers and the interconversion barriers among them were explored extensively at the DFT B3LYP-D3(BJ)/def2-TZVP and B3LYP-D3(BJ)/6-311++G(2d,p), as well as local MP2/aug-cc-pVQZ levels of theory, and 12 conformers were ultimately identified as possibly observable candidates in a molecular jet expansion. Rotational spectra of eight out of the 12 candidates were observed experimentally and analyzed. The non-observation of the remaining four conformers may be attributed to their low abundances. The study points out the importance of identifying all conformers of relevant abundance, even those which could not be detected experimentally, in order to properly benchmark the theoretical relative stabilities with the experimental ones. A comprehensive study of the conformational distribution of perillyl alcohol contributes to our understanding of its structural properties which may influence its functions.

Investigating the dissociation of acids in the presence of a limited number of water molecules is crucial for understanding various elementary chemical processes. In our study, focusing on HCl(H ₂ O) _n clusters (where HCl is hydrogen chloride and H ₂ O is water) formed in a cold and isolated jet expansion, we used the nuclear quadrupole coupling tensor obtained through rotational spectroscopy to decipher the nature of the hydrogen-chlorine (H-Cl) chemical bond in a microaqueous environment. For n = 1 to 4, the H-Cl bond is covalent. At n = 5 and 7, the contact ion pair of H ₃ O ⁺ Cl ⁻ is spontaneously formed within the hydrogen bond networks of book and cube acid-water clusters, respectively.

The initial stages of the gas‐phase nucleation between CO₂and monoethanolamine were investigated via broadband rotational spectroscopy with the aid of extensive theoretical structure sampling. Sub‐nanometer‐scale aggregation patterns of monoethanolamine‐(CO₂)_n,n=1–4, were identified. An interesting competition between the monoethanolamine intramolecular hydrogen bond and the intermolecular interactions between monoethanolamine and CO₂upon cluster growth was discovered, revealing an intriguing CO₂binding priority to the hydroxyl group over the amine group. These findings are in sharp contrast to the general results for aqueous solutions. In the quinary complex, a cap‐like CO₂tetramer was observed cooperatively surrounding the monoethanolamine. As the cluster approaches the critical size of new particle formation, the contribution of CO₂self‐assembly to the overall stability increases.

The chirality controlled conformational landscape of the trimer of propylene oxide (PO), a prototypical chiral molecule, was investigated using rotational spectroscopy and a range of theoretical tools for conformational searches and for evaluating vibrational contributions to effective structures. Two sets of homochiral (PO)₃ rotational transitions were assigned and the associated conformers identified with theoretical support. One set of heterochiral (PO)₃ transitions was assigned, but no structures generated by one of the latest, advanced conformational search codes could account for them. With the aid of a Python program, the carbon atom backbone and then the heterochiral (PO)₃ structure were generated using ¹³C isotopic data. Excellent agreement between theoretical and experimental rotational constants and relative dipole moment components of all three conformers was achieved, especially after applying vibrational corrections to the rotational constants.