The Gas-phase Reaction of NH₂ with Formaldehyde (CH₂O) is not a Source of Formamide (NH₂CHO) in Interstellar Environments

Abstract

The first experimental study of the low-temperature kinetics of the gas-phase reaction of NH2 with formaldehyde (CH2O) has been performed. This reaction has previously been suggested as a source of formamide (NH2CHO) in interstellar environments. A pulsed Laval nozzle equipped with laser-flash photolysis and laser-induced fluorescence spectroscopy was used to create and monitor the temporal decay of NH2 in the presence of CH2O. No loss of NH2 could be observed via reaction with CH2O, and we place an upper limit on the rate coefficient of <6 × 10−12 cm3 molecule−1 s−1 at 34 K. Ab initio calculations of the potential energy surface were combined with Rice–Rampsberger–Kassel–Marcus (RRKM) calculations to predict a rate coefficient of 6.2 × 10−14 cm3 molecule−1 s−1 at 35 K, consistent with the experimental results. The presence of a significant barrier, 18 kJ mol−1, for the formation of formamide as a product, means that only the H-abstraction channel producing NH3 + CHO, in which the transfer of an H atom can occur by quantum mechanical tunneling through a 23 kJ mol−1 barrier, is open at low temperatures. These results are in contrast with a recent theoretical study, which suggested that the reaction could proceed without a barrier and was therefore a viable route to gas-phase formamide formation. The calculated rate coefficients were used in an astrochemical model, which demonstrated that this reaction produces only negligible amounts of gas-phase formamide under interstellar and circumstellar conditions. The reaction of NH2 with CH2O is therefore not an important source of formamide at low temperatures in interstellar environments.

Experimental and theoretical study of the low-temperature kinetics of the reaction of CN with CH2O and implications for interstellar environments

“…Evidence for dimerization of CH 2 O was found in previous low-temperature studies at higher [CH 2 O] performed using a Laval nozzle, namely for rate coefficient determinations of the reactions OH + CH 2 O, 15 CH + CH 2 O, 14 and NH 2 + CH 2 O. 70 The range of values of the intercept (at [CH 2 O] = 0 molecule cm −3 ) was k int = 2200–7600 s −1 , and the variation of k̄ obs with [CH 2 O] without the subtraction of k int can be found in Fig. S3 of the ESI †.…”

“…15 CH + CH 2 O, 14 and NH 2 + CH 2 O. 70 The range of values of the intercept (at [CH 2 O] = 0 molecule cm -3 ) was k int = 2,200 -7,600 s −1 , and the variation of with [CH 2 O] without the subtraction 𝑘 𝑜𝑏𝑠 of k int can be found in Fig. S3 of the Supplementary Information.…”

Dramatic effect of the nature of R on the intrinsic acidity and basicity of potential astrochemical R–C≡COH and R–C≡CSH compounds

“…Many of the compounds detected in the interstellar medium are hard to be synthesized in the laboratory, and therefore, the information we have on their structure, properties and reactivity is fragmentary, and much of it comes from theoretical approaches. Indeed, mainly along the last decade, a lot of information on the reactivity of many potential astrochemical compounds came from high-level ab initio calculations [1][2][3][4][5][6][7][8]. In a similar way, it was possible to determine the structure of new or potential astrochemical compounds [9][10][11][12] or predict their existence and/ or their spectroscopic properties [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], or to explore their behavior in water or ice [27][28][29].…”

Peptide Bonds in the Interstellar Medium: Facile Catalytic Formation from Nitriles on Water–Ice Grains

“…The formation routes to formamide are still unclear; some have suggested gas-phase pathways via formaldehyde and amidogen: 6,7 + + but disputed by Song and Kastner 8 and convincingly refuted by Douglas et al 9 or surface reactions 10 by the hydrogenation of isocyanic acid, HNCO, and on carbon monoxide−ammonia ices: (1)…”