Rovibrationally Excited Molecules on the Verge of a Triple Breakdown: Molecular and Roaming Mechanisms in the Photodecomposition of Methyl Formate

Lombardi, Andrea; Palazzetti, Federico; Aquilanti, Vincenz̊o; Li, Hou-Kuan; Tsai, Po‐Yu; Kasai, Toshio; Lin, King‐Chuen

doi:10.1021/acs.jpca.6b00723

Cited by 22 publications

(54 citation statements)

References 57 publications

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“…Note that the CO produced in triple fragmentation (H + CO + OH) may be neglected, because the fraction of available energy partitioning into the internal energy of HCO is 0.13 33 . The internal energy obtained by HCO is about 22 kJ/mol, which is close to the dissociation energy threshold of H···CO (~5300 cm −1 ) 44,46,47 . While taking into account the energy partitioning into rotational degrees of freedom and other vibrational modes, the reaction HCO → H + CO becomes negligible.…”

Section: Resultssupporting

confidence: 64%

Roaming Dynamics and Conformational Memory in Photolysis of Formic Acid at 193 nm Using Time-resolved Fourier-transform Infrared Emission Spectroscopy

Tso

Kasai

Lin

2020

Sci Rep

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In photodissociation of trans-formic acid (HCOOH) at 193 nm, we have observed two molecular channels of co + H 2 o and co 2 + H 2 by using 1 μs-resolved fourier-transform infrared emission spectroscopy. With the aid of spectral simulation, the co spectra are rotationally resolved for each vibrational state (v = 1-8). Each of the resulting vibrational and rotational population distributions is characteristic of two Boltzmann profiles with different temperatures, originating from either transition state pathway or OH-roaming to form the same CO + H 2 o products. the H 2 o roaming co-product is also spectrally simulated to understand the interplay with the CO product in the internal energy partitioning. Accordingly, this work has evaluated the internal energy disposal for the CO and H 2 o roaming products; especially the vibrational-state dependence of the roaming signature is reported for the first time. Further, given a 1 μs resolution, the temporal dependence of the co/co 2 product ratio at v ≥ 1 rises from 3 to 10 of study, thereby characterizing the effect of conformational memory and well reconciling with the disputed results reported previously between absorption and emission methods.Roaming is recognized as one of the hottest topics in reaction dynamics for the past decade. For the most studied roaming cases of H 2 CO and CH 3 CHO 1-11 , following photodissociation a recoiling atom or radical fragment on the ground-state surface can roam and then abstract intramolecularly another H atom to generate the H 2 + CO and CH 4 + CO molecular products. This pathway is expected to open within the roaming window, in which the dissociation threshold of such a radical channel and the transition state (TS) of a molecular channel are close to each other. However, the roaming dynamics turns out to be more complicated to render studies oriented in varied directions 12-25 . As an example using carbonyl compounds in the photodissociation, aliphatic aldehydes showed a loose roaming saddle point along the roaming dissociation coordinate 26,27 , whereas the roaming signature in methyl formate (HCOOCH 3 ) was verified to involve multiple energy states via a conical intersection 17,18 . These two types of roaming dynamics apparently behave differently.Formic acid (HCOOH) belongs to the family of carbonyl compounds, and its photodissociation dynamics has been popularly investigated for more than two decades [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] . When its electronic band S 1 in the range 220 ∼ 250 nm is excited, the dissociation channel mainly contains HCO + OH with a quantum yield of 0.7∼0.8 30 . Because the excited surface is dissociative, the produced fragments bear very large translational energy 30,33 . Kim and co-workers 33 photolyzed the HCOOH molecule at 193 nm, and obtained a fraction of available energy into translational energy of OH as large as 0.82, whereas the fraction into internal energy of HCO was only 0.13. The fragments are mainly from the decomposition along the S 1 surface and the res...

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Section: Resultssupporting

confidence: 64%

Roaming Dynamics and Conformational Memory in Photolysis of Formic Acid at 193 nm Using Time-resolved Fourier-transform Infrared Emission Spectroscopy

Tso

Kasai

Lin

2020

Sci Rep

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“…5) is interestingly reminiscent of much investigated recent phenomena in photodissociation of molecules in neutral fragments. In the simplest ester HCOOCH 3 dissociating in CH 3 OH and CO, 47,48 a fraction of the latter is released later than expected: the simplified picture that may be adopted here is the promotion of the intermediate state to an upper slope of a conical intersection, followed either by a nearly vertical decay close to transition states (the direct mechanism leading to faster products) or delayed decay due to partial trapping in the conical intersection (the "roaming" mechanism leading to slower products).…”

Section: Ker Distributionsmentioning

confidence: 99%

Double photoionization of propylene oxide: A coincidence study of the ejection of a pair of valence-shell electrons

Falcinelli

Vecchiocattivi

Alagia

et al. 2018

The Journal of Chemical Physics

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Propylene oxide, a favorite target of experimental and theoretical studies of circular dichroism, was recently discovered in interstellar space, further amplifying the attention to its role in the current debate on protobiological homochirality. In the present work, a photoelectron-photoion-photoion coincidence technique, using an ion-imaging detector and tunable synchrotron radiation in the 18.0-37.0 eV energy range, permits us (i) to observe six double ionization fragmentation channels, their relative yields being accounted for about two-thirds by the couple (CH, CHO) and one-fifth by (CH, CHO); (ii) to measure thresholds for their openings as a function of photon energy; and (iii) to unravel a pronounced bimodality for a kinetic-energy-released distribution, fingerprint of competitive non-adiabatic mechanisms.

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“…Typically, roaming takes place on a flat region of the potential energy surface, thus allowing nascent reaction products to remain near each other long enough for further reactions to occur. Of particular interest to the work presented, recent studies have focused on roaming processes in small organic molecules such as acetaldehyde 20 – 22 , acetone 23 , methyl formate 24 – 26 , and propane 27 . In most cases, the roaming pathway contributes a small fraction of the total yield.…”

Section: Introductionmentioning

confidence: 99%

H2 roaming chemistry and the formation of H3+ from organic molecules in strong laser fields

et al. 2018

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Roaming mechanisms, involving the brief generation of a neutral atom or molecule that stays in the vicinity before reacting with the remaining atoms of the precursor, are providing valuable insights into previously unexplained chemical reactions. Here, the mechanistic details and femtosecond time-resolved dynamics of H3+ formation from a series of alcohols with varying primary carbon chain lengths are obtained through a combination of strong-field laser excitation studies and ab initio molecular dynamics calculations. For small alcohols, four distinct pathways involving hydrogen migration and H2 roaming prior to H3+ formation are uncovered. Despite the increased number of hydrogens and possible combinations leading to H3+ formation, the yield decreases as the carbon chain length increases. The fundamental mechanistic findings presented here explore the formation of H3+, the most important ion in interstellar chemistry, through H2 roaming occurring in ionic species.

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Rovibrationally Excited Molecules on the Verge of a Triple Breakdown: Molecular and Roaming Mechanisms in the Photodecomposition of Methyl Formate

Cited by 22 publications

References 57 publications

Roaming Dynamics and Conformational Memory in Photolysis of Formic Acid at 193 nm Using Time-resolved Fourier-transform Infrared Emission Spectroscopy

Roaming Dynamics and Conformational Memory in Photolysis of Formic Acid at 193 nm Using Time-resolved Fourier-transform Infrared Emission Spectroscopy

Double photoionization of propylene oxide: A coincidence study of the ejection of a pair of valence-shell electrons

H2 roaming chemistry and the formation of H3+ from organic molecules in strong laser fields

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