Temperature-dependent structural dynamics in covalent organic frameworks observed by cryogenic infrared spectroscopy.

Understanding the structural dynamics of covalent organic frameworks (COFs) in response to external temperature change is necessary for these materials' application at cryogenic temperatures. Herein, we report reversible structural dynamics observed in covalent organic frameworks as the temperature varies from 298 K to 30 K. A series of frameworks (COF-300, COF-300-amine, and COF-V) was studied using a cryogenic infrared spectroscopy system.

Direct Observation of Gas-Phase Hydroxymethylene: Photoionization and Kinetics Resulting from Methanol Photodissociation.

Carbene species play an integral role in high-energy chemistry, transition-metal-carbene chemistry, catalysis, photolytic formation of carbohydrates, and possibly even the formation of interstellar sugars. In 1921, "reactive formaldehyde"─now known as hydroxymethylene (HCOH)─was first implicated as an intermediate in photocatalytic processes. However, due to its transient nature, direct observation of HCOH has predominantly been attained using cryogenic isolation methods.

Matrix-formation dynamics dictate methyl nitrite conformer abundance.

Methyl nitrite has two stable conformational isomers resulting from rotation about the primary C-O-N-O dihedral angle: cis-CH3ONO and trans-CH3ONO, with cis being more stable by ∼5 kJ/mol. The barrier to rotational interconversion (∼45 kJ/mol) is too large for isomerization to occur under ambient conditions. This paper presents evidence of a change in conformer abundance when dilute CH3ONO is deposited onto a cold substrate; the relative population of the freshly deposited cis conformer is seen to increase compared to its gas-phase abundance, measured by in situ infrared spectroscopy.

Weakly Bound Complex Formation between HCN and CHCl: A Matrix-Isolation and Computational Study.

The matrix-isolated infrared spectrum of a hydrogen cyanide-methyl chloride complex was investigated in a solid argon matrix. HCN and CHCl were co-condensed onto a substrate held at 10 K with an excess of argon gas, and the infrared spectrum was measured using Fourier-transform infrared spectroscopy. Quantum chemical geometry optimization, harmonic frequency, and natural bonding orbital calculations indicate stabilized hydrogen- and halogen-bonded structures.

Intrinsic Structure and Electronic Spectrum of Deprotonated Biliverdin: Cryogenic Ion Spectroscopy and Ion Mobility.

We investigated the structural and spectroscopic properties of singly deprotonated biliverdin anions , using a combination of cryogenic ion spectroscopy, ion mobility spectrometry, and density functional theory. The ion mobility results show that at least two conformers are populated, with the dominant conformer at 75-90% relative abundance. The vibrational NH stretching signatures are sensitive to the tetrapyrrole structure, and they indicate that the tetrapyrrole system is in a helical conformation, consistent with simulated ion mobility collision cross sections.

Intrinsic photophysics of nitrophenolate ions studied by cryogenic ion spectroscopy.

The intrinsic photophysics of nitrophenolate isomers (meta, para, and ortho) was studied at low temperature using photodissociation mass spectrometry in a cryogenic ion trap instrument. Each isomer has distinct photophysics that affects the excited state lifetimes, as observed experimentally in their spectroscopic linewidths. Visible-light-induced excitation of m-nitrophenolate gives rise to well-resolved vibronic features in the spectrum of the S1 state.

Interactions of Molecular Titanium Oxides TiO ( x = 1-3) with Carbon Dioxide in Cluster Anions.

We study small titanium oxide-CO cluster anions in vacuo to understand the fundamental interactions between TiO and CO in the presence of an excess electron. Infrared spectra of [TiO (CO) ] ( x = 1-3, y > 1) were obtained using photodissociation spectroscopy and assigned through quantum chemistry calculations, identifying the formation of carbonato, oxalato, oxo, η-(O,O), and carbonyl ligands in the core ions of these clusters, with carbonato ligands being the dominant ligand species.

Vacuum ultraviolet photoionization cross section of the hydroxyl radical.

The absolute photoionization spectrum of the hydroxyl (OH) radical from 12.513 to 14.213 eV was measured by multiplexed photoionization mass spectrometry with time-resolved radical kinetics.

Gas-Phase Reactions of Isoprene and Its Major Oxidation Products.

Isoprene carries approximately half of the flux of non-methane volatile organic carbon emitted to the atmosphere by the biosphere. Accurate representation of its oxidation rate and products is essential for quantifying its influence on the abundance of the hydroxyl radical (OH), nitrogen oxide free radicals (NO ), ozone (O), and, via the formation of highly oxygenated compounds, aerosol. We present a review of recent laboratory and theoretical studies of the oxidation pathways of isoprene initiated by addition of OH, O, the nitrate radical (NO), and the chlorine atom.

Titanium Insertion into CO Bonds in Anionic Ti-CO Complexes.

We explore the structures of [Ti(CO) ] cluster anions using infrared photodissociation spectroscopy and quantum chemistry calculations. The existence of spectral signatures of metal carbonyl CO stretching modes shows that insertion of titanium atoms into C-O bonds represents an important reaction during the formation of these clusters. In addition to carbonyl groups, the infrared spectra show that the titanium center is coordinated to oxalato, carbonato, and oxo ligands, which form along with the metal carbonyls.

Characterization of Intermediate Oxidation States in CO Activation.

Redox chemistry during the activation of carbon dioxide involves changing the charge state in a CO molecular unit. However, such changes are usually not well described by integer formal charges, and one can think of COO functional units as being in intermediate oxidation states. In this article, we discuss the properties of CO and CO-based functional units in various charge states.

Structural Motifs of [Fe(CO)] Clusters (n = 3-7).

We present IR spectra and quantum chemical calculations for anionic iron-CO clusters of the form [Fe(CO)] (n = 3-7). All observed clusters have at least two CO units strongly bound to the metal atom. These strongly bound iron-CO complexes form the core ions of the clusters and are solvated by additional, weakly bound CO molecules.

VUV photoionization cross sections of HO2, H2O2, and H2CO.

The absolute vacuum ultraviolet (VUV) photoionization spectra of the hydroperoxyl radical (HO2), hydrogen peroxide (H2O2), and formaldehyde (H2CO) have been measured from their first ionization thresholds to 12.008 eV. HO2, H2O2, and H2CO were generated from the oxidation of methanol initiated by pulsed-laser-photolysis of Cl2 in a low-pressure slow flow reactor.

Photophysical and photochemical properties of the pharmaceutical compound salbutamol in aqueous solutions.

Salbutamol is a potent β(2)-adrenergic receptor agonist widely used in the treatment of bronchial asthma and chronic obstructive pulmonary disease. An increasing number of studies have detected salbutamol in natural water systems worldwide. Studies have shown that sunlight degrades salbutamol resulting in the formation of products; some showing higher toxicity to bacteria Vibrio fischeri than the parent compound.