Experimental and theoretical studies of the gas-phase reactions of O(¹D) with H₂O and D₂O at low temperature

Abstract

Measurements of the O(1D) + H2O, D2O reactions show that these processes become much more rapid below 100 K.

Kinetic study of the CN + C2H6 hydrogen abstraction reaction based on an analytical potential energy surface

“…Given that the RPMD method is exact at high temperatures (see, for instance, ref. 48–50 and 53–57), this agreement is indirect evidence of the quality of PES-2023. In the CVT method, the recrossing effect is evaluated as the ratio between CVT ( s = s *) and TST ( s = 0, saddle point) rate constants, i.e.…”

“…Previous studies have shown that the RPMD method can efficiently take account of the quantum effects, such as the ZPE and tunnelling, along the reaction pathway. 49,50 The RPMDrate input parameters are summarized in Table 2.…”

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

“…The original apparatus as described has been modified over the years to incorporate a tunable narrow-band VUV source for detection purposes. In this way, it has been possible to study the low-temperature reactivity of several atomic radicals such as C­( 3 P), , O­( 1 D), , N­( 2 D), , and C­( 1 D) [indirectly through product H­( 2 S) formation] , by exciting electronic transitions of these species in the 115–130 nm wavelength range. Despite the availability of Laval nozzles based on several different carrier gases including N 2 , SF 6 , and Ar, the present experiments were restricted to using argon-type nozzles as the rate constants for O­( 1 D) quenching by Ar are small enough (6–7 × 10 –13 cm 3 s –1 ) to allow kinetic measurements to be performed. , Indeed, N 2 is known to rapidly quench O­( 1 D) atoms at room temperature and below. , Three different nozzles were employed here, providing supersonic flows with characteristic temperatures of 127, 75, and 50 K with Ar as the carrier gas.…”

“…Mechanistically at room temperature and below, O( 1 D) atoms react with organic molecules predominantly by insertion into C-H and O-H bonds, forming long-lived intermediates such as CH3OH during the O( 1 D) + CH4 reaction and H2O2 during the O( 1 D) + H2O reaction before dissociating. 17,18,19,20,21 When CH3OH is employed as the coreagent species, as a bifunctional molecule two possibilities present themselves for the insertion process. Here, O( 1 D) can insert into either one of the C-H bonds of the CH3 moiety or into the O-H bond itself, leading to the possible formation of two distinct intermediate species, HOCH2OH following C-H insertion or CH3OOH formation following O-H insertion.…”

“…Mechanistically at room temperature and below, O­( 1 D) atoms react with organic molecules predominantly by insertion into C–H and O–H bonds, forming long-lived intermediates such as CH 3 OH during the O­( 1 D) + CH 4 reaction and H 2 O 2 during the O­( 1 D) + H 2 O reaction before dissociating. − When CH 3 OH is employed as the coreagent species, as a bifunctional molecule two possibilities present themselves for the insertion process. Here, O­( 1 D) can insert into either one of the C–H bonds of the CH 3 moiety or into the O–H bond itself, leading to the possible formation of two distinct intermediate species, HOCH 2 OH following C–H insertion or CH 3 OOH formation following O–H insertion. − While OH radicals are observed as the major product species, studies performed by selectively substituting H-atoms for D-atoms − clearly indicate that OH radicals are preferentially formed by dissociation of the CH 3 OOH intermediate, , whereas H-atoms are preferentially formed from the HOCH 2 OH intermediate (although this intermediate also contributes to OH formation), given that the CH 3 OOH dissociation toward both CH 2 OOH + H and CH 3 OO + H is an essentially thermoneutral process .…”