Issue 5, 2007

Millimetre wave spectroscopy of PANHs: phenanthridine

Abstract

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

Article information

Article type
Paper
Submitted
25 Oct 2006
Accepted
24 Nov 2006
First published
11 Dec 2006

Phys. Chem. Chem. Phys., 2007,9, 591-595

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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