Photoinitiated H2CO unimolecular decomposition: Accessing H+HCO products via S and T1 pathways

Valachovic, L.; Tuchler, Matthew F.; Dulligan, M.; Droz‐Georget, Th.; Zyrianov, M.; Kolessov, A.; Reisler, H.; Wittig, C.

doi:10.1063/1.480849

Cited by 61 publications

(76 citation statements)

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“…Recent experimental studies (Valachovic et al, 2000) of the radical channel have defined the energetics governing the competition between the S 0 and T 1 pathways, which are consistent with earlier experiments (Chuang et al, 1987) and with ab initio calculations (Yamaguchi et al, 1998). The T 1 route dominates at higher energies.…”

Section: Comments On Preferred Valuessupporting

confidence: 73%

“…For the molecular channel, the S 0 route, which is pressure quenched at energies below the radical threshold, may be replaced above the threshold by an 'abstraction' mechanism (v. Zee et al, 1993). This mechanism involves access to large H-HCO distances in the excited state just prior to bond breaking, which facilitate H-atom abstraction (Valachovic et al, 2000), producing H 2 +CO. This may resolve some of the earlier discrepancies concerning the yields of molecular products at higher energies Ho et al, 1982).…”

Section: Comments On Preferred Valuesmentioning

confidence: 99%

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Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species

et al. 2006

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Abstract. This article, the second in the series, presents kinetic and photochemical data evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of Organic species, which were last published in 1999, and were updated on the IUPAC website in late 2002, and subsequently during the preparation of this article. The article consists of a summary table of the recommended rate coefficients, containing the recommended kinetic parameters for the evaluated reactions, and eight appendices containing the data sheets, which provide information upon which the recommendations are made.

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Section: Comments On Preferred Valuessupporting

confidence: 73%

Section: Comments On Preferred Valuesmentioning

confidence: 99%

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species

et al. 2006

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“…Photodissociation of formaldehyde has been the subject of numerous theoretical and experimental studies (119)(120)(121)(122)(123)(124)(125)(126)(127)(128)(129)(130)(131)(132). It involves two decomposition and one isomerization channels: Downloaded by [George Mason University] at 02: 43 28 September 2014 whereas the isomerization of CH 2 O produces hydroxycarben, HCOH (125,126), the unimolecular decomposition generates H 2 +CO molecular and H • +HC • O radical products.…”

Section: Dehydrogenation Of Formaldehydementioning

confidence: 98%

Dihydrogen Catalysis: A Remarkable Avenue in the Reactivity of Molecular Hydrogen

Asatryan

Ruckenstein

2014

Catalysis Reviews

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Molecular hydrogen is the simplest and most abundant compound in the universe and is involved in numerous industrial chemical processes. In conventional chemistry, dihydrogen typically plays the role of a reductant and a reagent for homogeneous and heterogeneous hydrogenation processes such as the industrial and enzymatic ammonia formation, reduction of metallic ores and hydrogenation of unsaturated fats and oils. However, there are also processes in which molecular hydrogen participates as promoter, and even as catalyst. The catalytic role of the dihydrogen in free-valence migration in irradiated polymers and the interstellar isomerization of the formyl cation (protonated carbon monoxide) are well-documented examples of such processes. Recently, this issue has received new attention. Dihydrogen has been shown to play the role of a dehydrogenation catalyst (involving particularly metallocomplexes and inorganic materials), a relay (pass-on) transfer molecular agent and a transporter of protons.This review article, combined with original results, is focused on the mechanisms of the chemical processes where dihydrogen demonstrates catalytic behavior. We will call these processes (with somewhat broader meaning of the term) "dihydrogen catalysis" (DHC) which also includes the reactions mediated by transition metal dihydrides. Dihydrides are tentatively considered as pre-activated dihydrogen, coordinated to a metal center or implanted into a solid surface/support. DHC reactions are classified into five major reaction types: (i) dihydrogen-assisted relay transport of H-atoms (H2-RT); (ii) dihydrogen-assisted stepwise relay transport of H-atoms or of a free valence (sH2-RT); (iii) dihydrogen-assisted proton transport (H2-PT); (iv) dihydrogen-assisted dehydrogenation (H2-DeH); and (v) pre-activated dehydrogenation (PA-DeH). The classification of these mechanisms is Color versions of one or more of the figures in the article can be found online at www. tandfonline.com/lctr. 403 Downloaded by [George Mason University] at 02:43 28 September 2014 R. Asatryan and E. Ruckensteinbased on a detailed analysis of numerous potential energy surfaces studied by DFT and ab initio methods in conjunction with available experimental data. The H2-RT, H2-DeH, and PA-DeH processes occur via cyclic transition states. The relay H2-RT transport involves the H-H-H triad linked to both H-donor and H-acceptor centers, whereas the transition state ring in the H2-DeH dehydrogenation processes involves a H-H-H-H tetrad with the dihydrogen catalyst located in the middle. The H2-PT mechanism provides the transport of a proton mediated by dihydrogen combined in a triangular (H 3 + )-carrier unit. There are also practically important processes stimulated by dihydrogen such as the hydrogen spillover and hydrogen build-up in electronics, in which the catalytic role of dihydrogen is ambiguous, either because of the uncertainties in mechanisms, or prevailing traditional views. Some examples are briefly discussed in the framework of the concept of dihydrogen ...

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“…There is evidence that process B can occur either in the ground state or in the triplet state. 16 Previous studies on the photochemistry of aliphatic aldehydes at atmospherically relevant photolysis wavelengths focused on gasphase photodissociation [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and its pressure dependence. [31][32][33][34][35] Photolysis of aldehydes in a condensed matter environment, found for example in atmospheric aerosols, cloud and fog droplets, and in thin films formed on urban surfaces has not been systematically investigated.…”

Section: Introductionmentioning

confidence: 99%

Photochemistry of aldehyde clusters: cross-molecular versus unimolecular reaction dynamics

Shemesh

Blair

Nizkorodov

et al. 2014

Phys. Chem. Chem. Phys.

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The unimolecular photochemistry of aldehydes has been extensively studied, both experimentally and computationally. However, less is known about the role of cross-molecular photochemical processes in the condensed-phase photolysis of aldehydes. The triplet-state photochemistry of pentanal in its pentameric (n = 5) cluster was investigated as a model for photochemical reactions of aliphatic aldehydes in atmospheric aerosols. This study employs ''on the fly'' dynamics simulations using a semi-empirical MRCI electronic code for the singlet and triplet states involved. Previous studies have shown that the triplet-state photochemistry of an isolated pentanal molecule is dominated by Norrish I and II reactions. The main findings for the cluster are: (1) 55% of the trajectories lead to a unimolecular or cross-molecular reaction within a timescale of 100 ps; (2) cross-molecular reactions occur in over 70% of the reactive trajectories; (3) the main cross-molecular processes involve an H-atom transfer from the CHO group of the excited pentanal to an O atom of a nearby pentanal; and (4) the unimolecular Norrish II reaction is suppressed by the cluster environment. The predictions are qualitatively supported by experimental results on the condensed-phase photolysis of an aliphatic aldehyde, undecanal. The computational approach should be useful for predicting the mechanisms of other condensed-phase organic photochemical reactions. These results demonstrate a major role of cross-molecular processes in the condensed-phase photolysis of carbonyls. The cross-molecular reactions discussed in this work are relevant to photolysis-driven processes in atmospheric organic aerosols. It is expected that the condensed-phase environment of an organic aerosol particle should support a multitude of similar cross-molecular photochemical processes.

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Photoinitiated H2CO unimolecular decomposition: Accessing H+HCO products via S and T1 pathways

Cited by 61 publications

References 44 publications

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species

Dihydrogen Catalysis: A Remarkable Avenue in the Reactivity of Molecular Hydrogen

Photochemistry of aldehyde clusters: cross-molecular versus unimolecular reaction dynamics

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