These new data have enabled the determination of a very accurate set of spectroscopic parameters including rotational, quartic and sextic centrifugal distortion con-stants, as well as nuclear quadrupole coupling constants. Almost 1000 rotational transitions have been recorded for trans–anti and trans–syn allylimine. Guided by new laboratory data, allylimine was searched for in space using a sensitive spectral survey of the G+0.693-0.027 molecular cloud, located at the Galactic centre. High-level ab initio calculations were performed to assist the analysis and to obtain reliable estimates for an extended set of spectroscopic parameters. Measurements were performed using a source-modulation millimetre-wave spectrometer equipped with a pyrolysis system for the production of unstable species. The rotational spectra of the two most stable trans–anti and trans–syn geometrical isomers of allylimine were recorded in the laboratory in the 84–300 GHz frequency interval. The goal of the present work is to perform a comprehensive laboratory investigation of the rotational spectrum of allylimine in its ground vibrational state in order to obtain a highly precise set of rest frequencies to assist its search for astronomical sources. Therefore, allylimine (CH 2 =CH–CH=NH) represents a promising candidate for a new interstellar detection.Īims. Substituted methanimines and ethylenes have been identified in the interstellar medium. The molecular systems considered for benchmarking the TM-SE_LR scheme are those formally issued from addition/elimination reactions of nucleophilic unsaturated radicals (e.g., CN, C2H, and phenyl) to alkenes, imines, and aldehydes, whose rotational spectra have been investigated, but accurate structural determinations are not yet available.Ĭontext. The main outcome of our study is the reliability, robustness, and accuracy of this novel approach. Indeed, the latter parameters straightforwardly depend on the equilibrium geometry of the system under consideration. The resulting TM-SE_LR approach has been tested with respect to available SE equilibrium structures and rotational constants. The template molecule (TM) approach can be used to account for the modifications occurring when going from the isolated fragment to the molecular system under investigation, with the linear regression (LR) model employed to correct the linkage between the different fragments. This is based on the idea that a molecular system can be seen as formed by different fragments (the "Lego bricks"), whose accurate semi-experimental (SE) equilibrium geometries are available. The double-hybrid rev-DSD-PBEP86 functional already delivers remarkable results that can be further improved by means of a "Lego brick" model. For larger molecules, cheaper yet accurate approaches need to be defined. For small semi-rigid systems, state-of-the-art quantum-chemical computations can rival the most sophisticated experimental results. The accurate determination of equilibrium structures for isolated molecules plays a central role in the evaluation and interpretation of stereoelectronic, thermodynamic, and spectroscopic properties. The temperature dependence as well as possible mechanisms of the thermolysis process have been examined. A further characterization has been carried out by nuclear magnetic resonance spectroscopy, showing the feasibility of this synthetic approach in solution. Both E and Z isomers have been accurately characterized, thus providing a reliable basis to guide future astronomical observations. The combination of this formation pathway ‐based on the thermal decomposition of hydrobenzamide‐ with a state‐of‐the‐art computational characterization of phenylmethanimine laid the foundation for its first laboratory observation by means of rotational electric resonance spectroscopy. To tackle both aspects, a multidisciplinary approach has been exploited and a new, easily accessible synthetic approach to generate stable imine‐intermediates in the gas phase and in solution has been introduced. Phenylmethanimine is an aromatic imine with a twofold relevance in chemistry: organic synthesis and astrochemistry.
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