Kinetic Study of the Gas-Phase O(¹D) + CH₃OH and O(¹D) + CH₃CN Reactions: Low-Temperature Rate Constants and Atomic Hydrogen Product Yields

Abstract

Atomic oxygen in its first excited singlet state, O( 1 D), is an important species in the photochemistry of several planetary atmospheres and has been predicted to be a potentially important reactive species on interstellar ices. Here, we report the results of a kinetic study of the reactions of O( 1 D) with methanol, CH3OH, and acetonitrile, CH3CN, over the 50-296 K temperature range. A continuous supersonic flow reactor was used to attain these low temperatures coupled with pulsed laser photolysis and pulsed laser induced fluorescence to generate and monitor O( 1 D) atoms respectively. Secondary experiments examining the atomic hydrogen product channels of these reactions were also performed, through laser induced fluorescence measurements of H( 2 S) atom formation. On the kinetics side, the rate constants for these reactions were seen to be large (> 2 ´ 10 -10 cm 3 s -1 ) and consistent with barrierless reactions, although they display contrasting dependences as a function of temperature. On the product formation side, both reactions are seen to yield non-negligible quantities of atomic hydrogen. For the O( 1 D) + CH3OH reaction, the derived yields are in good agreement with the conclusions of previous experimental and theoretical work. For the O( 1 D) + CH3CN reaction, whose H-atom formation channels had not previously been investigated, electronic structure calculations of several new product formation channels were performed to explain the observed H-atom yields. These calculations demonstrate the barrierless and exothermic nature of the relevant exit channels, confirming that atomic hydrogen is also an important product of the O( 1 D) + CH3CN reaction.

The atmospheric relevance of primary alcohols and imidogen reactions

“… As is well known, for many atmospheric reactions by increasing in temperature and pressure, the rate of many atmospheric reactions is increased (the inverse behavior is observed for barrierless reactions). So, in high pressures and temperatures, the rate of some reacting species such as O 142 , F 143 , 144 , Cl 145 – 147 , and NH is the same as OH radicals or higher. Therefore, there is a competition between F, Cl, and 3 NH radicals for the elimination of atmospheric pollutants (like alcohols).…”

An experimental and theoretical investigation of the N(2D) + C6H6 (benzene) reaction with implications for the photochemical models of Titan

“…The principal attributes of this system have been presented in earlier work, 62 while the main modifications that have been made to allow us to follow the kinetics of atomic radical reactions are described in later work. 63–66 Three different Laval nozzles based on the carrier gases Ar or N 2 were employed during this investigation to access four different low temperature flows between 50 and 177 K (one nozzle was used with both Ar and N 2 to generate flows with characteristic temperatures of 127 and 177 K, respectively). The nozzle properties are summarized in Table 1 of Nuñez-Reyes et al 43 Room temperature measurements (296 K) were conducted with Ar as the carrier gas in the absence of a Laval nozzle and by reducing the flow velocity to avoid pressure gradients in the reactor.…”

“…The principal attributes of this system have been presented in earlier work, 62 while the main modifications that have been made to allow us to follow the kinetics of atomic radical reactions are described in later work. [63][64][65][66]…”

“…The principal attributes of this system have been presented in earlier work, 62 while the main modications that have been made to allow us to follow the kinetics of atomic radical reactions are described in later work. [63][64][65][66] Three different Laval nozzles based on the carrier gases Ar or N 2 were employed during this investigation to access four different low temperature ows between 50 and 177 K (one nozzle was used with both Ar and N 2 to generate ows with characteristic temperatures of 127 and 177 K, respectively).…”

Design of de Laval nozzles for gas-phase molecular studies in uniform supersonic flow

“…Furthermore, when following a reactive radical that is not in the ground state, the quenching of the radical is often given as an explanation for this intercept. 26,28, [95][96][97][98][99][100][101][102][103][104][105][106][107] One also notes that intrinsic fluorescence has also been put forward as an explanation. 108 Actually, the idea of quenching or intrinsic fluorescence formally amounts to take into account one or multiple secondary reactions in competition.…”