Formation of N-bearing complex organic molecules in molecular clouds: Ketenimine, acetonitrile, acetaldimine, and vinylamine via the UV photolysis of C$_2$H$_2$ ice

K. -J. Chuang; C. Jäger; J. C. Santos; Th. Henning

paper

Formation of N-bearing complex organic molecules in molecular clouds: Ketenimine, acetonitrile, acetaldimine, and vinylamine via the UV photolysis of C $_{2}$ H $_{2}$ ice

arXiv:2405.07855

Abstract

The solid-state C $_{2}$ H $_{2}$ chemistry in interstellar H $_{2}$ O-rich ice has been proposed to explain astronomically observed complex organic molecules (COMs), including ketene (CH $_{2}$ CO), acetaldehyde (CH $_{3}$ CHO), and ethanol (CH $_{3}$ CH $_{2}$ OH), toward early star-forming regions. This formation mechanism is supported by recent laboratory studies and theoretical calculations for the reactions of C $_{2}$ H $_{2}$ +OH/H. However, the analog reaction of C $_{2}$ H $_{2}$ +NH $_{2}$ forming N-bearing species has been suggested to have a relatively low rate constant that is orders of magnitude lower than the value of C $_{2}$ H $_{2}$ +OH. This work extends our previous laboratory studies on O-bearing COM formation to investigate the interactions between C $_{2}$ H $_{2}$ and NH $_{3}$ ice triggered by cosmic ray-induced secondary UV photons under molecular cloud conditions. Experiments were performed in an ultra-high vacuum chamber to investigate the UV photolysis of the C $_{2}$ H $_{2}$ :NH $_{3}$ ice mixture at 10 K. The studied ice chemistry of C $_{2}$ H $_{2}$ with NH $_{2}$ radicals and H atoms resulting from the UV photodissociation of NH $_{3}$ leads to the formation of several N-bearing COMs, including vinylamine (CH $_{2}$ CHNH $_{2}$ ), acetaldimine (CH $_{3}$ CHNH), acetonitrile (CH $_{3}$ CN), ketenimine (CH $_{2}$ CNH), and tentatively ethylamine (CH $_{3}$ CH $_{2}$ NH $_{2}$ ). The experimental results show an immediate and abundant CH $_{2}$ CHNH $_{2}$ yield as the first-generation product, which is further converted into other chemical derivatives. The effective destruction and formation cross-section values of parent species and COMs were derived, and we discuss the chemical links among these molecules and their astronomical relevance.

22 pages, 9 figures

Formation of N-bearing complex organic molecules in molecular clouds: Ketenimine, acetonitrile, acetaldimine, and vinylamine via the UV photolysis of C2​H2​ ice

Abstract

Formation of N-bearing complex organic molecules in molecular clouds: Ketenimine, acetonitrile, acetaldimine, and vinylamine via the UV photolysis of C $_{2}$ H $_{2}$ ice