3 research outputs found
Electronic Spectroscopy of 1‑(Phenylethynyl)naphthalene
Recently 1-(phenylethynyl)Ânaphthalene
(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 S<sub>1</sub> state lies at 30823 cm<sup>–1</sup>, 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<sup>–1</sup> (S<sub>0</sub>) and 17 cm<sup>–1</sup> (S<sub>1</sub>) 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<sup>–1</sup>, 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
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Exclusive p encapsulation of light alkali metal cations by a neutral molecule
Cation-p interactions are one of the most important classes of non-covalent bonding, and are seen throughout biology, chemistry and materials science. However, in almost every documented case, these interactions play only a supporting role to much stronger covalent or dative bonds, making examples of exclusive cation-p bonding exceedingly rare. In this work, a neutral diboryne molecule is found to encapsulate the light alkali metal cations Li+ and Na+ in the absence of a net charge, covalent bonds, or lone-pair donor groups. The resulting encapsulation complexes are to our knowledge the first structurally authenticated species in which a neutral molecule binds the light alkali metals exclusively through cation-p interactions
Experimental Assessment of the Strengths of B–B Triple Bonds
Diborynes, molecules
containing homoÂatomic boron–boron
triple bonds, have been investigated by Raman spectroscopy in order
to determine the stretching frequencies of their central Bî—¼B
units as an experimental measure of homoatomic bond strengths. The
observed frequencies between 1600 and 1750 cm<sup>–1</sup> were
assigned on the basis of DFT modeling and the characteristic pattern
produced by the isotopic distribution of boron. This frequency completes
the series of known stretches of homoatomic triple bonds, fitting
into the trend established by the long-known stretching frequencies
of Cî—¼C and Nî—¼N triple bonds in alkynes and dinitrogen,
respectively. A quantitative analysis was carried out using the concept
of relaxed force constants. The results support the classification
of the diboryne as a true triple bond and speak to the similarities
of molecules constructed from first-row elements of the p block. Also
reported are the relaxed force constants of a recently reported diborabutatriene,
which again fit into the trend established by the vibrational spectroscopy
of organic cumulenes. As part of these studies, a new diboryne with
decreased steric bulk was synthesized, and a computational study of
the rotation of the stabilizing ligands indicated alkyne-like electronic
isolation of the central B<sub>2</sub> unit