How CO Affects the Composition of Titan’s Tholins Generated with Electron Cyclotron Resonance Plasma

Abstract Titan’s atmosphere possesses thick haze layers, but their formation mechanisms remain poorly understood, including the influence of oxygen-containing gas components on organic matter synthesis. As the most abundant oxygen-containing gas, the presence of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">CO</mml:mi> </mml:math> has been found to exert a significant impact on the generation of oxygen-containing organic compounds. Therefore, investigating the influence of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">CO</mml:mi> </mml:math> on the production and composition of tholins through laboratory simulations holds profound scientific significance in the context of Titan. The work presented here is an experimental simulation designed to evaluate the impact of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">CO</mml:mi> </mml:math> on the atmospheric chemistry of Titan. To this end, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">CO</mml:mi> </mml:math> was introduced into the standard <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">N</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:mi mathvariant="normal">C</mml:mi> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msub> </mml:math> mixture at varying mixing ratios from 0.2% to 9% and exposed to electron cyclotron resonance plasma to initiate photochemical reactions. Optical emission spectroscopy was employed for gas-phase in situ characterization, while infrared spectroscopy and high-resolution mass spectrometry were used to analyze the resulting solid products (tholins). Our results demonstrate that the addition of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">CO</mml:mi> </mml:math> enriches the complexity of the chemical system. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">CO</mml:mi> </mml:math> not only supplies oxygen to the system but also enhances nitrogen’s reactivity and incorporation, enhancing the number and quantity of the organic products.