Laser-Induced Chemistry Observed during 248 nm Vacuum Ultraviolet Photolysis of an O3 and CH3NH2 Mixture.

We present an examination of the 248 nm VUV (vacuum ultraviolet) laser photolysis of an ozone (O3) and methylamine (CH3NH2) mixture as means to produce aminomethanol (NH2CH2OH). Aminomethanol is predicted to be the direct interstellar precursor to glycine and is therefore an important target for detection in the interstellar medium. However, due to its high reactivity under terrestrial conditions, aminomethanol evades gas-phase spectral detection. The insertion of O(1D) into methylamine is one proposed pathway to form aminomethanol. However, this formation pathway is highly exothermic and results in a complex mixture of reaction products, complicating spectral assignment. Additional reactions between methylamine and the other products of ozone photolysis lead to further complication of the chemistry. Here, we present a systematic experimental study of these reaction pathways. We have used direct absorption millimeter/submillimeter spectroscopy in a supersonic expansion to probe the reaction products, which include formaldehyde (H2CO), methanimine (CH2NH), formamide (HCONH2), and hydrogen cyanide (HCN) and absorption signals arising from at least two additional unknown products. In addition, we examine the effects of reaction time on the chemical formation pathways and discuss them in the context of O(1D) insertion chemistry with methylamine. We have built a kinetics box model to interpret the results that are observed. We then examine the implications of these results for future studies aimed at forming and detecting aminomethanol.

Quantum Mechanical Enhancement of Rate Constants and Kinetic Isotope Effects for Water-Mediated Proton Transfer in a Model Biological System.

Biological systems have been shown to shuttle excess protons long distances by taking advantage of tightly organized hydrogen-bonded water bridges in hydrophobic protein cavities, and similar effects have been observed in carbon nanotubes. In this theoretical study we investigate how quantum effects of proton motion impact the rate constants for charge transfer in a model system consisting of a donor and acceptor molecule separated by a single-molecule water bridge. We calculate quantum and classical rate constants for the transfer of an excess proton over two possible paths, one with an H3O+ intermediate, and one with an OH- intermediate. Quantum effects are included through ring polymer molecular dynamics (RPMD) calculations. We observe a 4-fold enhancement of reaction rate constants due to proton tunneling at temperatures between 280 and 320 K, as shown by transmission coefficient calculations. Deuteration of the donor and acceptor proton are shown to decrease the reaction rate constant by a factor of 50, and this is another indicator that tunneling plays an important role in this proton transfer mechanism.