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

Abstract

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.

Experimental identification of aminomethanol (NH2CH2OH)—the key intermediate in the Strecker Synthesis

“…An alternative pathway to 1 could comprise the barrierless insertion of an electronically excited oxygen atom (O( 1 D)) into a carbon-hydrogen bond of the methyl group of methylamine (reaction (6); Fig. 1) [20][21][22] followed by stabilization of the aminomethanol insertion product either by a third body collision in the gas phase or through energy transfer processes to the surrounding molecules within an icy matrix. Furthermore, the rate of unimolecular decomposition of aminomethanol (NH 2 CH 2 OH) to methanimine (CH 2 NH) will significantly reduce in a nonaqueous medium containing reactants methylamine and oxygen.…”