Observation of a core-excited dipole-bound state ∼1 eV above the electron detachment threshold in cryogenically cooled acetylacetonate.

Dipole-bound states in anions exist when a polar neutral core binds an electron in a diffuse orbital through charge-dipole interaction. Electronically excited polar neutral cores can also bind an electron in a diffuse orbital to form Core-Excited Dipole-Bound States (CE-DBSs), which are difficult to observe because they usually lie above the electron detachment threshold, leading to very short lifetimes and, thus, unstructured transitions. We report here the photodetachment spectroscopy of cryogenically cooled acetylacetonate anion (C5H7O2-) recorded by detecting the neutral radical produced upon photodetachment and the infrared spectroscopy in He-nanodroplets.

The temperature variation of the CH + H reaction rate coefficients: a puzzle finally understood?

CH was the first molecular ion identified in the interstellar medium and is found to be ubiquitous in interstellar clouds. However, its formation and destruction paths are not well understood, especially at low temperatures. A new theoretical approach based on the canonical variational transition state theory was used to study the H + CH reactive collisions.

Understanding the active role of water in laboratory chamber studies of reactions of the OH radical with alcohols of atmospheric relevance.

In this work, we studied the reactions of three cyclic aliphatic alcohols with OH at room temperature, atmospheric pressure and different humidities in a Teflon reaction chamber. It was determined that the lower the solubility of the alcohol in water, the larger the effect of the humidity on the acceleration of the reaction. This experimental evidence allows suggesting that the acceleration is due to the reaction of the co-adsorbed reactants at the air-water interface of a thin water film deposited on the Teflon walls of the reaction chamber, instead of between co-reactants dissolved in the water film or due to gas phase catalysis as previously suggested.

Photodetachment of Deprotonated R-Mandelic Acid: The Role of Proton Delocalization on the Radical Stability.

The photodetachment and stability of R-Mandelate, the deprotonated form of the R-Mandelic acid, was investigated by observing the neutral species issued from either simple photodetachment or dissociative photodetachment in a cold anions set-up. R-Mandalate has the possibility to form an intramolecular ionic hydrogen-bond between adjacent hydroxyl and carboxylate groups. The potential energy surface along the proton transfer (PT) coordinate between both groups (O …H … OCO) features a single local minima, with the proton localized on the O group (OH… OCO).

Inter- and Intramolecular Proton Transfer in an Isolated (Cytosine-Guanine)H Pair: Direct Evidence from IRMPD Spectroscopy.

The collision-induced dissociation of the protonated cytosine-guanine pair was studied using tandem mass spectrometry (MS) coupled to infrared multiple photon dissociation spectroscopy with the free electron laser at Orsay (CLIO) to determine the structure of the CH and GH ionic fragments. The results were rationalized with the help of electronic structure calculations at the density functional theory level with the B3LYP/6-311++G(3df,2p) method. Several tautomers of each fragment were identified for the first time, some of which were previously predicted by other authors.

Rate Coefficient and Mechanism of the OH-Initiated Degradation of 1-Chlorobutane: Atmospheric Implications.

In this work, we investigate the degradation process of 1-chlorobutane, initiated by OH radicals, under atmospheric conditions (air pressure of 750 Torr and 296 K) from both experimental and theoretical approaches. In the first one, a relative kinetic method was used to obtain the rate coefficient for this reaction, while the products were identified for the first time (1-chloro-2-butanone, 1-chloro-2-butanol, 4-chloro-2-butanone, 3-hydroxy-butanaldehyde, and 3-chloro-2-butanol) using mass spectrometry, allowing suggesting a reaction mechanism. The theoretical calculations, for the reactive process, were computed using the BHandHLYP/6-311++G(d,p) level of theory, and the energies for all of the stationary points were refined at the CCSD(T) level.

Dissociative photodetachment vs. photodissociation of aromatic carboxylates: the benzoate and naphthoate anions.

The competition between dissociative photodetachment and photodissociation of cold benzoate and naphthoate anions was studied through measurement of the kinetic energy of the neutral fragments and intact parent benzoyloxy and naphtoyloxy radicals as well as by detecting the anionic fragments whenever they are produced. For the benzoate anion, there is no ionic photodissociation and the radical dissociation occurs near the vertical photodetachment energy. This is in agreement with DFT calculations showing that the dissociation energy in CO2 and C6H5˙ is very low.

Water catalysis of the reaction between hydroxyl radicals and linear saturated alcohols (ethanol and n-propanol) at 294 K.

The rate coefficients for the reactions of OH with ethanol and n-propanol were determined by a relative method in a smog chamber at 294 K, 1 atm of air or N2 and a wide range of humidity. The rate coefficients for both reactions show a quadratic dependence on the water concentration as in the case of the reaction of OH with methanol (Jara-Toro et al. Angew.

Water Catalysis of the Reaction between Methanol and OH at 294 K and the Atmospheric Implications.

The rate coefficient for the reaction CH OH+OH was determined by means of a relative method in a simulation chamber under quasi-real atmospheric conditions (294 K, 1 atm of air) and variable humidity or water concentration. Under these conditions, a quadratic dependence of the rate coefficient for the reaction CH OH+OH on the water concentration was found. Thus the catalytic effect of water is not only important at low temperatures, but also at room temperature.