The 130–370 GHz rotational spectrum of phenyl isocyanide (C6H5NC)

Abstract

The analysis of phenyl isocyanide (C 6 H5NC, µa = 4.0 D) in its ground vibrational state and two lowest-energy excited vibrational states, ν 22 (141 cm −1) and ν 33 (155 cm −1), in the 130-370 GHz frequency region has been completed. Over 4500 new rotational transitions have been measured in the ground vibrational state for the most abundant isotopologue, resulting in the determination of the spectroscopic constants for a partial octic Hamiltonian with low error. The Coriolis-coupled ν 22-ν 33 dyad reported herein, containing over 3500 new transitions for each vibrational state, has been analyzed for the first time. The coupled-state least-squares fit utilizes seven coupling terms (Ga, G J a , G K a , G JJ a , G JK a , F bc , and F K bc) to address perturbation between the two vibrational states, including resonances and several nominal interstate transitions. This work results in precise determination of the energy separation between the two states, ∆E 22,33 = 9.682 248(3) cm −1 , and the Coriolis coupling coefficient, |ζ a 22,33 | = 0.858(9). The precise rotational and distortion constants determined in this work provide the foundation for an astronomical search for phenyl isocyanide across the radio band.

Semi-Experimental Equilibrium (reSE) and Theoretical Structures of Pyridazine (o-C4H4N2)

“…The rotational spectrum of pyridazine, previously reported in the frequency range of 235–360 GHz, was measured from 130 to 375 GHz using a rotational spectrometer described elsewhere. ,, A commercial sample of pyridazine was used without purification at a sample pressure of 0.5–7 mTorr at room temperature using a continuous flow. The spectral ranges were combined into a single broadband spectrum and each species was least-squares fit to a distorted-rotor Hamiltonian using Assignment and Analysis of Broadband Spectra (AABS) software. , PLANM and AC programs were used for data analysis .…”

“…As a prototypical aromatic heterocycle, , it is a species of astrochemical relevance. − Benzene has been detected in the interstellar medium by infrared spectroscopy, but it cannot be observed by radioastronomy because it lacks a permanent dipole moment. Aromatic compounds that are polar by virtue of inherent structural factors, − heteroatom substitution, − or polar substituents − have been important targets for astronomical detection (Figure ). The recent detections of polar aromatic compounds by radioastronomy (benzonitrile and cyanonaphthalenes) represent dramatic breakthroughs in astrochemistry and will undoubtedly inspire new searches for aromatic heterocycles.…”

The eight lowest-energy vibrational states of benzonitrile: analysis of Coriolis and Darling-Dennison couplings by millimeter-wave and far-infrared spectroscopy

“…Benzonitrile is among numerous examples of molecules exhibiting vibrationally excited state couplings successfully analyzed via either rotational or high-resolution infrared spectroscopy [10,11,[29][30][31][32][33][34][35][36][37][38]. Our previous work on benzonitrile [28] updated the spectroscopic constants using millimeter-wave data up to 360 GHz and analyzed for the first time the Coriolis-coupled dyad of its two lowest-energy fundamental states, 22 (141 cm −1 [20,39], B1 symmetry) and 33 (163 cm −1 [20,39], B2 symmetry).…”

Synthesis, Purification, and Rotational Spectroscopy of (Cyanomethylene)Cyclopropane—An Isomer of Pyridine

“…Organic nitriles occupy a significant place in the field of astrochemistry and are well represented in the list of ∼220 species detected in space. , Their large molecular dipole moments, due to the cyano moiety, result in intense rotational transitions that facilitate identification of these species by radioastronomy. We have been keenly interested in measuring spectroscopic constants of organic nitriles in two groups: aryl nitriles/isonitriles − and nitrile-containing isomers of pyridine. − The former group was inspired by the potential of these aryl species to serve as tracers for their parent compounds ( e . g ., benzene, pyridine, pyridazine, pyrimidine, and pyrazine).…”