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Issue 5, 2007
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Millimetre wave spectroscopy of PANHs: phenanthridine

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The pure rotational spectrum of phenanthridine (C13H9N), a small polycyclic aromatic nitrogen heterocycle (PANH), has been measured from 48 to 85 GHz employing Stark modulated millimetre wave absorption spectroscopy of a supersonic rotationally cold molecular beam. Initial survey search scans were guided by rotational constants obtained through quantum chemical calculations performed at the B3LYP/cc-pVTZ level of theory. Close agreement—to well within 1%—is found between the calculated equilibrium and experimentally derived ground state rotational constants. From the moments of inertia a substantial negative inertial defect of Δ = −0.4688(44) amu Å2 is obtained which can be explained by the presence of several energetically low-lying out-of-plane vibrational modes. Corresponding density functional theory calculations of harmonic fundamental frequencies indeed yield four such low frequency modes with values as low as 96 cm−1. The data presented here will also be useful for deep radio astronomical searches for PANHs employing large radio telescopes.

Graphical abstract: Millimetre wave spectroscopy of PANHs: phenanthridine

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Publication details

The article was received on 25 Oct 2006, accepted on 24 Nov 2006 and first published on 11 Dec 2006

Article type: Paper
DOI: 10.1039/B615485A
Citation: Phys. Chem. Chem. Phys., 2007,9, 591-595
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    Millimetre wave spectroscopy of PANHs: phenanthridine

    D. McNaughton, P. D. Godfrey, R. D. Brown and S. Thorwirth, Phys. Chem. Chem. Phys., 2007, 9, 591
    DOI: 10.1039/B615485A

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