title: Millimetre wave spectroscopy of PANHs: phenanthridine.
abstract: The pure rotational spectrum of phenanthridine (C(13)H(9)N), 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 Delta = -0.4688(44) amu Angstroms(2) 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.
authors.affiliation: School of Chemistry, Monash University, Clayton, Victoria, Australia. Don.McNaughton@sci.monash.edu.au
authors.forename: Don
authors.initials: D
authors.lastname: McNaughton
authors.forename: Peter D
authors.initials: PD
authors.lastname: Godfrey
authors.forename: Ronald D
authors.initials: RD
authors.lastname: Brown
authors.forename: Sven
authors.initials: S
authors.lastname: Thorwirth
mesh_terms: D007834:Lasers; D008872:Microwaves; D015394:Molecular Structure; D010617:Phenanthridines / Q000737:chemistry*; D011789:Quantum Theory; D012399:Rotation; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis; D014732:Vibration
chemical_list: D010617:Phenanthridines