Gas‐Phase Photodissociation of CH<sub>3</sub>CHBrCOCl at 248 nm: Detection of Molecular Fragments by Time‐Resolved FT‐IR Spectroscopy

Liu, Chia-Yun; Tsai, Max; Tsai, Po‐Yu; Liu, Yuting; Chen, Si Ying; Chang, Agnes H. H.; Lin, King‐Chuen

doi:10.1002/cphc.201000713

Cited by 10 publications

(4 citation statements)

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“…The apparatus, employed throughout in all the experiments for the above carbonyl compounds, contains a step-scan FTIR emission spectroscope for the spectral detection of the fragments and a sixway stainless steel cube as a reaction chamber in which a multi-pass optical system is housed. 16,[20][21][22] The multi-pass optical system, composed of two pairs of 2 00 -diameter gold-coated curved mirrors and positioned perpendicular to the laser propagation direction, was used to enhance the IR emission signal-to-noise ratio.…”

Section: Time-resolved Ftir Emission Spectroscopymentioning

confidence: 99%

Regulation of nonadiabatic processes in the photolysis of some carbonyl compounds

Lin

2016

Phys. Chem. Chem. Phys.

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Carbonyl compounds studied are confined to acetyl halide (CH3COCl), acetyl cyanide (CH3COCN), acetyl sulfide (CH3COSH), acetaldehyde (CH3CHO), and methyl formate (HCOOCH3). They are asymmetrically substituted, but do not follow the well-known Norrish type I reactions. Each compound ejected in an effusive beam at about 300 K is commonly excited to the (1)(n, π*)CO lower state; that is, a nonbonding electron on O of the C[double bond, length as m-dash]O group is promoted to the antibonding orbital of π*CO. The photolysis experiments are conducted in the presence of Ar gas and the corresponding fragments are detected using time-resolved Fourier-transform Infrared (FTIR) emission spectroscopy. The enhancement of the collision-induced internal conversion or intersystem crossing facilitates the dissociation channels via highly vibrational states of the ground singlet (So) or triplet (T1) potential energy surfaces. In this manner, an alternative nonadiabatic channel is likely to open yielding different products, even if the diabatic coupling strength is strong between the excited state and the neighboring state. For instance, the photodissociation of CH3COCl at 248 nm produces HCl, CO, and CH2 fragments, in contrast to the supersonic jet experiments showing dominance of the Cl fragment eliminated from the excited state. If the diabatic coupling strength is weak, dissociation proceeds mainly through internal conversion, such as the cases of CH3COCN and CH3COSH. The photodissociation of CH3COCN at 308 nm has never been reported before, while for CH3COSH matrix-isolated photodissociation was conducted that shows a distinct spectral feature from the current FTIR method. The CH3CHO and HCOOCH3 molecules belong to the same type of carbonyl compounds, in which the molecular products, CO + CH4 and CO + CH3OH, are produced through both transition state and roaming pathways. Their products are characterized differently between molecular beam and current FTIR experiments. For instance, the photodissociation of HCOOCH3 at 248 nm yields CO with the vibrational state v ≥ 4, in contrast to the molecular beam experiments producing CO at v = 1. The photodissociation of CH3CHO at 308 nm intensifies a low energy component in the CH4 vibrational distribution, thus verifying the transition state pathway for the first time.

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Section: Time-resolved Ftir Emission Spectroscopymentioning

confidence: 99%

Regulation of nonadiabatic processes in the photolysis of some carbonyl compounds

Lin

2016

Phys. Chem. Chem. Phys.

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“…Time-resolved FTIR emission spectroscopy [51][52][53][54][55] with some modification was employed in this work, as illustrated in Fig. S5.…”

Section: Methodsmentioning

confidence: 99%

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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“…6,[27][28][29] In brief, it contained a step-scan FTIR emission spectrometer for spectral detection of the fragments and a six-way stainless steel cube as reaction chamber. The photolysis laser propagated through the sample beam ejected from an effusive nozzle, and the fragment emission signals were guided along a perpendicular axis to focus onto the entrance of the FTIR spectrometer.…”

Section: Methodsmentioning

confidence: 99%

Photodissociation of gaseous CH3COSH at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Observation of three dissociation channels

Tsai

Fan

et al. 2013

The Journal of Chemical Physics

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Upon one-photon excitation at 248 nm, gaseous CH(3)C(O)SH is dissociated following three pathways with the products of (1) OCS + CH(4), (2) CH(3)SH + CO, and (3) CH(2)CO + H(2)S that are detected using time-resolved Fourier-transform infrared emission spectroscopy. The excited state (1)(n(O), π*(CO)) has a radiative lifetime of 249 ± 11 ns long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of collision-induced internal conversion is estimated to be 1.1 × 10(-10) cm(3) molecule(-1) s(-1). Among the primary dissociation products, a fraction of the CH(2)CO moiety may undergo further decomposition to CH(2) + CO, of which CH(2) is confirmed by reaction with O(2) producing CO(2), CO, OH, and H(2)CO. Such a secondary decomposition was not observed previously in the Ar matrix-isolated experiments. The high-resolution spectra of CO are analyzed to determine the ro-vibrational energy deposition of 8.7 ± 0.7 kcal/mol, while the remaining primary products with smaller rotational constants are recognized but cannot be spectrally resolved. The CO fragment detected is mainly ascribed to the primary production. A prior distribution method is applied to predict the vibrational distribution of CO that is consistent with the experimental findings.

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Gas‐Phase Photodissociation of CH₃CHBrCOCl at 248 nm: Detection of Molecular Fragments by Time‐Resolved FT‐IR Spectroscopy

Cited by 10 publications

References 40 publications

Regulation of nonadiabatic processes in the photolysis of some carbonyl compounds

Regulation of nonadiabatic processes in the photolysis of some carbonyl compounds

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

Photodissociation of gaseous CH3COSH at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Observation of three dissociation channels

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Gas‐Phase Photodissociation of CH3CHBrCOCl at 248 nm: Detection of Molecular Fragments by Time‐Resolved FT‐IR Spectroscopy

Cited by 10 publications

References 40 publications

Regulation of nonadiabatic processes in the photolysis of some carbonyl compounds

Regulation of nonadiabatic processes in the photolysis of some carbonyl compounds

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

Photodissociation of gaseous CH3COSH at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Observation of three dissociation channels

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Gas‐Phase Photodissociation of CH₃CHBrCOCl at 248 nm: Detection of Molecular Fragments by Time‐Resolved FT‐IR Spectroscopy