An Experimental and Theoretical Investigation of the Gas-Phase C(³P) + N₂O Reaction. Low Temperature Rate Constants and Astrochemical Implications

Abstract

The reaction between atomic carbon in its ground electronic state, C( 3 P), and nitrous oxide, N2O, has been studied below room temperature due to its potential importance for astrochemistry, with both species considered to be present at high abundance levels in a range of interstellar environments. On the experimental side, we measured rate constants for this reaction over the 50-296 K range using a continuous supersonic flow reactor. C( 3 P) atoms were generated by the pulsed photolysis of carbon tetrabromide at 266 nm and were detected by pulsed laser induced fluorescence at 115.8 nm. Additional measurements allowing the major product channels to be elucidated were also performed. On the theoretical side, statistical rate theory was used to calculate low temperature rate constants. These calculations employed the results of new electronic structure calculations of the 3 A² potential energy surface of CNNO and provided a basis to extrapolate the measured rate constants to lower temperatures and pressures. The rate constant was found to increase monotonically as the temperature falls (𝑘 !( ! #)%& " ' (296 K) = (3.4 ± 0.3) ´ 10 -11 cm 3 s -1 ), reaching a value of 𝑘 !( ! #)%& " ' (50 K) = (7.9 ± 0.8) ´ 10 -11 cm 3 s -1 at 50 K. As current astrochemical models do not include the C + N2O reaction, we tested the influence of this process on interstellar N2O and other related species using a gas-grain model of dense interstellar clouds. These simulations predict that N2O abundances decrease significantly at intermediate times (10 3 -10 5 years) when gas-phase C( 3 P) abundances are high.

Kinetic Study of the Gas-Phase Reaction between Atomic Carbon and Acetone: Low-Temperature Rate Constants and Hydrogen Atom Product Yields

“…Over the past few years, we have begun to address this issue by examining the reactivity of C( 3 P) with important COMs such as CH 3 OH 14 and CH 3 CN 15 and other molecules that are thought to be formed primarily on interstellar ices such as N 2 O. 5 At the present time, the chemical processes leading to the formation of many of the observed interstellar COMs are not well constrained in a general sense. Among them, acetone, Sgr B2 (OH) by Combes et al 16 in 1987 with a derived column density of 5 × 10 13 cm −2 corresponding to a relative abundance (with respect to H 2 ) of 5 × 10 −11 .…”

“…Although there are numerous studies of the kinetics − and dynamics ,− of C( 3 P) reactions with a wide range of unsaturated hydrocarbons, there are relatively few studies of its reactions with organic molecules containing other types of functional groups such as those found in complex organic molecules (COMs). Over the past few years, we have begun to address this issue by examining the reactivity of C( 3 P) with important COMs such as CH 3 OH and CH 3 CN and other molecules that are thought to be formed primarily on interstellar ices such as N 2 O …”

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]…”

10 Years of the ACS PHYS Astrochemistry Subdivision

“…20 However, this is hardly the only novel result. In this virtual special issue, N 2 O is reacted with C( 3 P), producing rate coefficients for such chemical processes, 21 and a similar study on fluoromethane and calcium atomic cations is also reported. 22 Additionally, the deuterated ethynyl radical is reacted with propylene producing a wealth of hydrocarbons, 23 NO + the propargyl radical generates branching ratios for eight common astrochemical products, 24 furan + H 2 reactions generate various c-C 4 H x O (x = 4−8) species, 25 myriad nitrous oxides are synthesized in H 2 O−N 2 O/N 2 ice mixtures, 26,27 dinitriles are shown to be produced from gas-phase reactions of cyano radicals and cyanoethane, 28 and porous amorphous solid water appears to catalyze interstellar organic chemistry.…”