Conformational analysis

The saturated part of the 1,2,3,4-tetrahydroquinoline (THQ) molecule allows for the possibility of multiple conformers' existence. High-resolution microwave spectroscopy, supported by high-level quantum chemistry calculations, was used to determine the precise molecular structures of the conformers of THQ. Via the MP2 calculations, we were able to discriminate four stable conformations, i.e. two pairs of energetically equivalent enantiomorphic conformers. The results of the calculations also indicate that energetically non-equivalent conformers are separated by a low energy barrier (104 cm(-1)) that allows for conformational cooling to occur. The high resolution rotational spectrum with resolved hyperfine structure in the frequency range of 7-20 GHz was obtained using both the In-phase/quadrature-phase-Modulation Passage-Acquired-Coherence Technique (IMPACT) and the coaxially oriented beam resonator arrangement (COBRA) to perform Fourier transform microwave (FTMW) spectroscopy. The precise values of the rotational constants, N-14 nuclear hyperfine coupling parameters and centrifugal distortion parameters were determined from the measured transition frequencies. Based on our experimental results, only the most stable enantiomeric pair of THQ contributes to the rotational spectrum under the conditions of our experiment as the less stable conformers seem to efficiently relax to the lower energy conformers. Thus the experimentally evaluated molecular constants unambiguously define the lowest energy conformer of 1,2,3,4-tetrahydroquinoline.

Determination of the global PES

Formation of precise radial functions globally describing spin-rotation-vibration states of diatomics The radial molecular functions provide knowledge not only of the molecular properties, but also about the molecular interactions with the environment in which they are located (e.g. with a present optical, electric or magnetic field). A highly accurate ab initio radial function of a given property can be homotopically morphed to available experimental data, creating thus its only a few-parameter topologically correct approximant. The function is generated across the entire range of the vibrational displaments (including the dissociation asymptote), allowing thus accurate predicting for the so-far unobserved molecular states. Therefore, the functions provide a needed base for studying a very broad class of chemical and physical processes observed both terrestrially and extra-terrestrially.

Identification of species in the Universe

A high degree of isomerism in the realm of interstellar molecules stimulates systematic astronomical investigations of members of different families of isomers. Among them, vinyl-bearing compounds have kindled considerable interest due to recent detections of vinylamine, vinylacetylene, and vinylcyanoacetylene. Herein, we open the possibility to search for vinylketene in the interstellar space by means of its rotational transitions. The pure rotational spectrum of the title molecule was recorded in the frequency regions 195–218 and 293–324 GHz and an improved and extended set of spectroscopic parameters has been obtained for the most stable trans conformer. In addition, rotational signatures and molecular constants for the less stable cis form are reported for the first time. We provide a catalog of precise transition frequencies and intensities of vinylketene to the astronomical community and pave the way toward interstellar explorations of C4H4O isomer family.