RESUMEN
Quantitative determination of multiple transient species is critical in investigating reaction mechanisms and kinetics under various conditions. Dual-comb spectroscopy, a comb-laser-based multi-heterodyne interferometric technique that enables simultaneous achievement of broadband, high-resolution, and rapid spectral acquisition, opens a new era of time-resolved spectroscopic measurements. Employing an electro-optic dual-comb spectrometer with central wavelength near 3 µm coupled with a Herriott multipass absorption cell, here we demonstrate simultaneous determination of multiple species, including methanol, formaldehyde, HO2 and OH radicals, and investigate the reaction kinetics. In addition to quantitative spectral analyses of high-resolution and tens of microsecond time-resolved spectra recorded upon flash photolysis of precursor mixtures, we determine a rate coefficient of the HO2 + NO reaction by directly detecting both HO2 and OH radicals. Our approach exhibits potential in discovering reactive intermediates and exploring complex reaction mechanisms, especially those of radical-radical reactions.
RESUMEN
Molecular spectroscopy in the mid-infrared spectral range is expected to present fingerprints of chemical species that provide a unique identification with adequate sensitivity. Dual-comb spectroscopy, a promising successor to conventional Fourier-transform spectroscopy, enables rapid molecular fingerprinting with high-resolution and high-precision. Here, we report gas-phase transmittance and dispersion spectra by employing a rapidly tunable dual-comb spectrometer based on electro-optic frequency combs near 3 µm. The tunable spectral range >550 cm-1 and adjustable optical resolutions from a few hundred MHz to a few GHz were demonstrated. With the capabilities of wavelength agility and easily adjustable comb-mode spacing, the spectra of nitrous oxide and its isotopes were measured with Doppler-limited resolution. Furthermore, the N2-broadened spectra of acetylene were recorded to derive the collisional broadening coefficient. Fast acquisitions with adequate spectral resolution were also achieved within sub-microseconds. Both precision spectral metrology and fast molecular sampling could be implemented by employing the high-flexible dual-comb spectrometer.
RESUMEN
Striding to extend the length of metal-atom strings, oligo-α-pyridylamino ligands are modulated with naphthyridyl moieties leading to the undeca-nickel mixed-valence complexes [Ni11(bnatpya)4Cl2]4+ (1) and [Ni11(bnatpya)4Cl2]2+ (2). The first single-molecule conductance measurements of a linear undeca-nickel chain were performed.
RESUMEN
The new ligand, 2-(α-(5-phenyl)pyridylamino)-1,8-naphthyridine (Hphpyany), was synthesised by a palladium(0)-catalysed reaction of 2-chloro-1,8-naphthyridine with 2-amino-5-phenylpyridine in the presence of potassium tert-butoxide. Linear tetranickel metal complexes, [Ni4(phpyany)4Cl2](CF3SO3) 1, [Ni4(phpyany)4Cl2](BF4)22, [Ni4(phpyany)4(NCS)2](ClO4) 3 and [Ni4(phpyany)4(NCS)2](CF3SO3)24 were prepared and crystallographically characterised. Complexes 1-4 demonstrate that, for the first time, four asymmetric ligands align unidirectionally and thus configure (4,0)-form tetranickel strings, specifically, with the phenyl groups of the four phpyany- pointing to one side of the Ni4 chain and naphthyridyl to the other. The remarkably short Ni-Ni distances (ca. 2.33 Å) for 1 and 3 indicate partial metal-metal bonding, which can be viewed as both complexes containing one mixed-valence Ni23+ unit. The measurements of the magnetic susceptibility reveal that Ni47+ complexes 1 and 3 exhibit antiferromagnetic interactions (J = -42 cm-1 for 1 and -46 cm-1 for 3) between the terminal Ni2+ ion and the Ni23+ unit, while Ni48+ complexes 2 and 4 exhibit antiferromagnetic interactions (J = -33 cm-1 for 2 and -35 cm-1 for 4) between the two terminal Ni2+ ions. The results of the cyclic voltammetry indicate the presence of two reversible redox couples at E1/2(1) = 0.12 V, E1/2(2) = -0.65 V for 1, and at E1/2(1) = 0.12 V, E1/2(2) = -0.72 V for 3. The products of the first oxidation for 1 and 3 are the oxidised species 2 and 4, respectively. The values of single-molecule resistance (15.4 (±3.46) MΩ for 3 and 16.2 (±5.04) MΩ for 4) were determined by STM-based break-junction methods. The results represent the first conductance measurements of linear tetranickel chains.
RESUMEN
The use of single-molecule junctions for various functions constitutes a central goal of molecular electronics. The functional features and the efficiency of electron transport are dictated by the degree of energy-level alignment (ELA), that is, the offset potential between the electrode Fermi level and the frontier molecular orbitals. Examples manifesting ELA are rare owing to experimental challenges and the large energy barriers of typical model compounds. In this work, single-molecule junctions of organometallic compounds with five metal centers joined in a collinear fashion were analyzed. The single-molecule i-V scans could be conducted in a reliable manner, and the EFMO levels were electrochemically accessible. When the electrode Fermi level (EF ) is close to the frontier orbitals (EFMO ) of the bridging molecule, larger conductance was observed. The smaller |EF -EFMO | gap was also derived quantitatively, unambiguously confirming the ELA. The mechanism is described in terms of a two-level model involving co-tunneling and sequential tunneling processes.