Electronic Spectroscopy of 1‑(Phenylethynyl)naphthalene

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 118; no. 16; pp. 2915 - 2921
• Main Authors: Constantinidis, Philipp, Lang, Melanie, Herterich, Jörg, Fischer, Ingo, Auerswald, Johannes, Krueger, Anke
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.04.2014
• Subjects: Combustion; Dimerization; Electronics; Excitation; Ionization; Origins; Spectroscopy; Thresholds
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp412482p

Recently 1-(phenylethynyl)naphthalene (1-PEN) was suggested to be the primary dimerization product of phenylpropargyl radicals and therefore an important polycyclic hydrocarbon in combustion processes. Here we describe a spectroscopic investigation of a genuine 1-PEN sample by several complementary techniques, infrared spectroscopy, multiphoton ionization (MPI), and threshold photoelectron spectroscopy. The infrared spectrum recorded in a gas cell confirms that 1-PEN is indeed the previously observed dimerization product of phenylpropargyl. The origin of the transition into the electronically excited S1 state lies at 30823 cm–1, as found by MPI. Considerable vibrational activity is observed, and a number of low-wavenumber bands are assigned to a progression in the torsional motion. Values of 6 cm–1 (S0) and 17 cm–1 (S1) were derived for the fundamental of the torsion. In the investigated energy range the excited state lifetimes are in the nanosecond range. Spectra of the 1-PEN/Ar cluster exhibit a red shift of the electronic origin of 22 cm–1, in good agreement with other aromatic molecules. A threshold photoelectron spectrum recorded using synchrotron radiation yields an ionization energy of 7.58 eV for 1-PEN. An excited electronic state of the cation is found at 7.76 eV, and dissociative photoionization does not set in below 15 eV.