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We observed the products C 4 H 5 , C 4 H 4 , C 3 H 3 and CH 3 of the C( 3 P) + C 3 H 6 reaction using product time-of-flight spectroscopy and selective photoionization. The identified species arise from the product channels C 4 H 5 + H, C 4 H 4 + 2H and C 3 H 3 + CH 3 . Product isomers were identified via measurements of photoionization spectra and calculations of adiabatic ionization energy. Product C 4 H 5 probably involves three isomers HCCCHCH 3 , H 2 CCCCH 3 and H 2 CCCHCH 2 . In contrast, products C 4 H 4 and C 3 H 3 involve exclusively HCCCHCH 2 and H 2 CCCH, respectively. Reaction mechanisms are unraveled with crossed-beam experiments and quantum-chemical calculations. The 3 P carbon atom attacks the π orbital of propene (C 3 H 6 ) to form a cyclic complex c -H 2 C(C)CHCH 3 that rapidly opens the ring to form H 2 CCCHCH 3 followed by decomposition to HCCCHCH 3 /H 2 CCCCH 3 /H 2 CCCHCH 2 + H and H 2 CCCH + CH 3 ; the corresponding branching ratios are 7:5:10:78 predicted with RRKM calculations at collision energy 4 kcal mol −1 . Nascent C 4 H 5 with enough internal energy further decomposes to HCCCHCH 2 + H. Ratios of products C 4 H 5 , C 4 H 4 and C 3 H 3 are experimentally evaluated to be 17:8:75. This work provides a comprehensive look at product channels of the title reaction and gives implications for the formation of hydrocarbons in extra-terrestrial environments such as Titan and carbon-rich interstellar media. We suggest that the title reaction, hitherto excluded in any chemical networks, needs to be taken into account at least in the atmosphere of Titan and carbon-rich molecular clouds where rapid neutral–neutral reactions are dominant and carbon atoms and propene are abundant.

We investigated the title reaction at collision energy 3.5 kcal mol(-1) in a crossed molecular beam apparatus using undulator radiation as an ionization source. Time-of-flight (TOF) spectra of product C(3)H(3) were measured in laboratory angles from 20° to 100° using two photoionization energies 9.5 and 11.6 eV. These two sets of experimental data exhibit almost the same TOF distributions and laboratory angular distributions. From the best simulation, seven angle-specific kinetic-energy distributions and a nearly isotropic angular distribution are derived for product channel C(3)H(3) + H that has an average kinetic-energy release of 15.5 kcal mol(-1), corresponding to an average internal energy of 33.3 kcal mol(-1) in C(3)H(3). Furthermore, TOF spectra of product C(3)H(3) were measured at laboratory angle 52° with ionizing photon energies from 7 to 12 eV. The appearance of TOF spectra remains almost the same, indicating that a species exclusively contributes to product C(3)H(3); the species is identified as H(2)CCCH (propargyl) based on the ionization energy of 8.6 ± 0.2 eV and the maximal kinetic-energy release of 49 kcal mol(-1). Theoretical calculations indicate that the rapid inversion mechanism and rotation in intermediate H(2)CCCH(2) can result in a forward-backward symmetric angular distribution for product C(3)H(3) + H. The present work avoids the interference of reactions of C((1)D) and C(2) radicals with C(2)H(4) and rules out the probability of production of other isomers like c-C(3)H(3) and H(3)CCC proposed in the previous work at least at the investigated collision energy.

We have measured, by means of ultrafast x-ray absorption and optical spectroscopy, the M-O (M=Fe, Co) and Co-N metal to ligand bond length change as a function of time and the formation and decay of the excited states and intermediate species, after excitation with a 267 nm femtosecond pulse. These experimental data combined with DFT calculations allowed us to determine the mechanism of electron transfer operating in the redox reaction of two metal-ligand complexes, [M(III)(C2O4)3]3- and [Co(III)(NH3)6 ]3+. Based on the data we find that, even though both molecules are excited into their charge transfer band, the redox reaction of [M(III)(C2O4)3]3- proceeds via intermolecular electron transfer while [Co(III)(NH3)6 ]3+ electron transfer mechanism is intramolecular.

We report the studies of ultrafast dynamics of azobenzene cations using femtosecond photoionization-photofragmentation spectroscopy. In our experiment, a femtosecond pump pulse first prepares an ensemble of azobenzene cations via photoionization of neutrals. A delayed probe pulse then brings the evolving ionic system to higher states that ultimately undergo ion fragmentation. The dynamics is followed by monitoring either the parent-ion depletion or fragment-ion formation as a function of the pump-probe delay time. The observed transients for azobenzene cations are characterized by a constant ion depletion modulated by a rapidly damped oscillatory signal with a period of about 1 ps. Theoretical calculations suggest that the oscillation arises from a vibration motion along the twisting inversion coordinate involving displacements in CNNC and phenyl-ring torsions. The oscillation is damped rapidly with a time constant of about 1.2 ps, suggesting that energy dissipation from the active mode to bath modes takes place on this time scale.

We measured time-of-flight (TOF) spectra of products from the reaction O( 3 P/ 1 D) + C 2 H 4 at collision energy 6.4 kcal mol −1 using a quadrupole mass filter and tunable vacuum-ultraviolet light for ionization. All carbon-containing products from five exit channels – CH 2 CHO + H, CH 2 CO + H 2 , CH 3 + HCO, CH 2 + HCHO, and CH 2 CO + 2H – were identified. Product channels CH 2 CHO + H and CH 2 CO + 2H associate with 3 P and 1 D atomic oxygen reactants, respectively. Both 3 P and 1 D oxygen reactants might be responsible for the other reactions. The ionization threshold of nascent vinoxy radicals is 9.3 ± 0.1 eV.

The deuterium isotope effect in the photodissociation of acetone S2 state was studied using femtosecond pump–probe ionization spectroscopy. The transients obtained for both isotopomers can be well described by the same mechanism in which the primary dissociation occurs on the S1 surface. Substantial isotope effects were observed in every stage of the reaction. Our results indicted that upon full deuteration the initial-state decay from S2 to S1 slows down by a factor of three, the subsequent adiabatic dissociation on the S1 surface slows down by a factor of four, and the secondary dissociation slows down by a factor of ∼1.6.

The photodissociation dynamics of the acetone S 2 (n,3s) Rydberg state has been studied by using femtosecond pump–probe multiphoton ionization mass spectrometry. Acetone was excited at 195 nm and the temporal evolutions of the initial state and intermediates were monitored. We considered two mechanisms: (1) the conventionally accepted mechanism, in which the primary dissociation occurs on the first triplet-state surface; and (2) the newly proposed mechanism by the Zewail’s group, in which the primary dissociation takes place on the first singlet-state surface. The conventional mechanism was found to be inadequate to describe the observed dynamics. On the other hand, our results and analyses supported the validity of the new mechanism.

The photodissociation of two acyl cyanide compounds, R–C(O)–CN, where R=methyl and tert-butyl groups, has been investigated using femtosecond time-resolved laser-induced fluorescence (LIF) spectroscopy. Both compounds were excited by two-photon excitation at a total energy of ∼6.4 eV and the formation of the free CN(X) radical products was probed in real time by monitoring the CN X→B LIF signal. The results revealed that the temporal evolution of the CN(X) formation can be well characterized by delayed biexponential rise functions with time constants in the picosecond time scale, indicating that the dissociation occurs via a complex-mode mechanism. We proposed a dissociation mechanism involving two discernable stages to account for the observed temporal behaviors as well as previous photofragment translational spectroscopic results reported by other groups. Our analyses suggested that the selectivity between the C–CN and C–R bond cleavage is determined by the competition between the adiabatic and nonadiab...

The photodissociation of cyanobenzene (C 6 H 5 CN) at a high energy of ∼9.6 eV near the ionization threshold has been investigated using femtosecond time-resolved laser-induced fluorescence (LIF) spectroscopy. Cyanobenzene molecules were excited by three-photon excitation at 388.6 nm and the temporal evolution of the free CN(X) fragment formation was probed in real time by monitoring the CN X → B LIF signal. The results revealed that the CN(X) products are formed on three very different timescales, suggesting that the dissociation proceeds through at least three dissociation pathways at such a high energy.

We investigated the dynamics of the reaction of (3)P atomic carbon with propene (C3H6) at reactant collision energy 3.8 kcal mol(-1) in a crossed molecular-beam apparatus using synchrotron vacuum-ultraviolet ionization. Products C4H5, C4H4, C3H3, and CH3 were observed and attributed to exit channels C4H5 + H, C4H4 + 2H, and C3H3 + CH3; their translational-energy distributions and angular distributions were derived from the measurements of product time-of-flight spectra. Following the addition of a (3)P carbon atom to the C=C bond of propene, cyclic complex c-H2C(C)CHCH3 undergoes two separate stereoisomerization mechanisms to form intermediates E- and Z-H2CCCHCH3. Both the isomers of H2CCCHCH3 in turns decompose to C4H5 + H and C3H3 + CH3. A portion of C4H5 that has enough internal energy further decomposes to C4H4 + H. The three exit channels C4H5 + H, C4H4 + 2H, and C3H3 + CH3 have average translational energy releases 13.5, 3.2, and 15.2 kcal mol(-1), respectively, corresponding to fractions 0.26, 0.41, and 0.26 of available energy deposited to the translational degrees of freedom. The H-loss and 2H-loss channels have nearly isotropic angular distributions with a slight preference at the forward direction particularly for the 2H-loss channel. In contrast, the CH3-loss channel has a forward and backward peaked angular distribution with an enhancement at the forward direction. Comparisons with reactions of (3)P carbon atoms with ethene, vinyl fluoride, and vinyl chloride are stated.

The mechanism responsible for the redox reaction of [Co(III)(en)3]Ac3 to Co(II) complex has been determined to be intramolecular electron transfer. It was measured in real time by means of subpicosecond extended X-ray absorption fine structure spectra, EXAFS, and optical experiments and supported by density functional theory calculations. The proposed mechanism is based on histograms of bond length changes of the transient structures measured as a function of time, with subpicosecond time and sub-Angstrom resolution and femtosecond transient spectra and kinetics after excitation with a 267 nm femtosecond pulse. Even though four Fe and Co complexes were excited in the charge transfer band and the photoinduced redox reaction proceeds with similar high redox quantum yield, the dominant electron operating mechanism differs: intramolecular for amine metal complexes and intermolecular for oxalate metal complexes. The ligand orientation degree of freedom and counterion effect are proposed to provide tentative explanation for the electron transfer mechanism.

We report studies of ultrafast dynamics of azobenzene cation using femtosecond photoionization-photofragmentation spectroscopy. In our experiments, a femtosecond pump pulse first produces an ensemble of azobenzene cations via photoionization of the neutrals. A delayed probe pulse then brings the evolving ionic system to excited states that ultimately undergo ion fragmentation. The dynamics is followed by monitoring either the parent-ion depletion or fragment-ion formation as a function of the pump-probe delay time. The observed transients for azobenzene cation are characterized by a constant ion depletion modulated by a rapidly damped oscillatory signal with a period of about 1 ps. Theoretical calculations suggest that the oscillation arises from a vibration motion along the twisting inversion coordinate involving displacements in CNNC and phenyl-ring torsions. The oscillation is damped rapidly with a time constant of about 1.2 ps, suggesting that energy dissipation from the active mode to bath modes takes place in this time scale.

In a crossed molecular-beam apparatus, we reacted atomic O in states (3)P and (1)D with ethene (C(2)H(4)) at collision energy 3 kcal mol(-1). Employing two mixtures, 20% O(2) + 80% He and 3% O(2) + 12.5% Ar + 84.5% He, as discharge media allowed us to generate two sources of oxygen atoms that have the same mean velocity but different ratios of (1)D/(3)P populations, 0.0017 and 0.035. We identified six reactions and recorded time-of-flight spectra of products CH(2)CHO, CH(2)CO, and CH(3) as a function of laboratory angle. Reaction O((3)P) + C(2)H(4) --CH(2)CHO + H has a fraction f(t) = 0.43 of energy release in translation, and product CH(2)CHO has a maximal probability at scattering angle of 140 degrees. For reaction O((1)D) + C(2)H(4) --CH(2)CO + 2H, f(t) = 0.26, and the angular distribution of product CH(2)CO shows a backward preference. For reaction O((3)P) + C(2)H(4) --CH(2)CO + H(2), f(t) = 0.35, and the angular distribution of product CH(2)CO has a slight preference for a sideways direction. In contrast, reaction O((1)D) + C(2)H(4) --CH(2)CO + H(2) has f(t) = 0.26 and an angular distribution with forward and backward peaking and symmetry. Reactions O((3)P and (1)D) + C(2)H(4) --CH(3) + HCO have f(t) = 0.09 and 0.08, respectively, and angular distributions with forward and backward peaking and nearly symmetric. The reactivity of O (1)D with ethene is ca. 38 and 90 times that of O (3)P for channels to eliminate H(2) and CH(3), respectively. For reactions of O (1)D, the branching ratio for elimination of 2H is ca. 3.3 times that for elimination of H(2).

Using a quadrupole mass filter and vacuum-ultraviolet ionization, we measured the time-of-flight spectra of species at mass-to-charge ratios of m/ z = 45-42 from the reaction of N + SiH 4 in crossed molecular beams. Species with m/ z = 44 and 43 correspond to reaction products HSiNH/SiNH 2 and HSiN/HNSi, respectively; species with m/ z = 45 and 42 are assigned to isotopic variants and daughter ions, respectively, of those two reaction products. We measured the photoionization yields and branching ratios for dissociative ionization of reaction products as a function of photoionization energy. The ionization thresholds of products HSiNH/SiNH 2 and HSiN/HNSi were determined to be 6.7 and 9.2 eV, respectively. Furthermore, we calculated the equilibrium structures, electronic energies, and vibrational wavenumbers of various silicon-nitrogen hydrides H x SiNH y ( x + y = 0-3) using quantum-chemical methods. SiNH 2 (X (2)B 2) and HNSi (X (1)Sigma (+)) are more stable than HSiNH (X (2)A') and HSiN (X (1)Sigma (+)) by 0.82 and 2.81 eV, respectively. SiNH 2 (X (2)B 2), HSiNH (X (2)A'), HNSi (X (1)Sigma (+)), and HSiN (X (1)Sigma (+)) have adiabatic ionization energies of 6.81, 8.19, 10.21, and 10.23 eV, respectively. These experimental and calculated results indicate that SiNH 2 (X (2)B 2) and HNSi (X (1)Sigma (+)) are dominant among isomeric products in the reaction of N + SiH 4. This work presents the first observation of products from the reaction of N + SiH 4 in crossed beams and extensive calculations on pertinent silicon-nitrogen hydrides.

We report the study of photodissociation dynamics of dimethyl sulfoxide at 200 nm using femtosecond pump−probe spectroscopy. The temporal behaviors of all major reaction products were measured. The nearly instantaneous (50 fs) appearance of the SO product strongly suggests the existence of a dissociation pathway that breaks the two equivalent S−C bonds in a concerted manner.

The photodissociation dynamics of the acetone S2 (n, 3s) Rydberg state excited at 195 nm has been studied by using femtosecond pump-probe mass-selected multiphoton ionization spectroscopy. For the first time, the temporal evolutions of the initial state, intermediates, and methyl products were simultaneously measured and analyzed for this reaction to elucidate the complex dynamics. Two mechanisms were considered: (1) the commonly accepted mechanism in which the primary dissociation occurs on the first triplet-state surface, and (2) the recently proposed mechanism in which the primary dissociation takes place on the first singlet-excited-state surface. Our results and analyses supported the validity of the new mechanism. On the other hand, the conventional mechanism was found to be inadequate to describe the observed dynamics. The temporal evolution of methyl products arising from the secondary dissociation of hot acetyl intermediates exhibited a very complex behavior that can be ascribed to the combination of a nonuniform initial vibrational distribution and the competition between dissociation and slow intramolecular vibrational redistribution.

The dynamics of the C((3)P) + C2H3Cl reaction at collision energy 3.8 kcal mol(-1) was investigated in a crossed molecular-beam apparatus using synchrotron vacuum-ultraviolet ionization. Time-of-flight spectra of products C3H2Cl, C3H3, and Cl were recorded at various laboratory scattering angles, from which translational-energy distributions and angular distributions of product channels C3H2Cl + H and C3H3 + Cl were derived. Cl correlates satisfactorily with C3H3 in linear momentum and angular distributions, which confirms the production of C3H3 + Cl. The H-loss (Cl-loss) channel has average translational-energy release 14.3 (8.8) kcal mol(-1) corresponding to a fraction 0.30 (0.14) of available energy into the translational degrees of freedom of product HCCCHCl + H (H2CCCH + Cl). The branching ratio of channel H to channel Cl was determined approximately as 12:88. The measurements of translational-energy releases and photoionization thresholds cannot distinguish HCCCHCl from H2CCCCl because both isomers have similar enthalpy of formation and ionization energy; nevertheless, the Rice-Ramsperger-Kassel-Marcus calculation prefers HCCCHCl. The measurement of photoionization spectra identifies product C3H3 as H2CCCH (propargyl). Both products C3H2Cl + H and C3H3 + Cl might correlate to the same triplet intermediate H2CCCHCl but have distinct angular distributions; the former is nearly isotropic whereas the latter is forward biased. A comparison with the C((3)P) + C2H3F reaction is stated.

Two product channels C3H2F + H and C3H3 + F were identified in the reaction of C((3)P) atoms with vinyl fluoride (C2H3F) at collision energy 3.7 kcal mol(-1) in a crossed molecular-beam apparatus using selective photoionization. Time-of-flight (TOF) spectra of products C3H2F and C3H3 were measured at 12-16 laboratory angles as well as a TOF spectrum of atomic F, a counter part of C3H3, was recorded at single laboratory angle. From the best simulation of product TOF spectra, translational-energy distributions at seven scattering angles and a nearly isotropic (forward and backward peaked) angular distribution were derivable for exit channel C3H2F + H (C3H3 + F) that has average kinetic-energy release of 14.5 (4.9) kcal mol(-1). Products C3H2F + H and C3H3 + F were estimated to have a branching ratio of ~53:47. Furthermore, TOF spectra and photoionization spectra of products C3H2F and C3H3 were measured at laboratory angle 62° with photoionization energy ranging from 7 eV to 11.6 eV. The appearance of TOF spectra is insensitive to photon energy, implying that only single species overwhelmingly contributes to products C3H2F and C3H3. HCCCHF (H2CCCH) was identified as the dominant species based on the measured ionization threshold of 8.3 ± 0.2 (8.6 ± 0.2) eV and the maximal translational-energy release. The C/H and C/F exchange mechanisms are stated.

We utilize 100 fs optical pulses as a means of heating 150 nm thick single Au (111) crystals, below the melting point and monitor the subsequent structural evolution with subpicosecond time resolution using 0.6 ps, 8.04 KeV x-ray pulses. By monitoring the energy and time dependent modulation of the width and shift of the x-ray diffraction rocking curve, we have obtained information on electron-phonon coupling, photon-lattice interaction, and time resolved kinetics of the crystal disorder. The data show that during the first couple picoseconds after optical excitation, the formation of a “blast force” and lattice contraction, followed by a pressure wave formed 10-20 ps later. Both the blast and pressure wave propagate through the crystal with sonic velocities. These time resolved x-ray diffraction data provide a detail description of the processes induced by ultrafast laser pulses impinging on very thin metallic crystals.

We investigated the reaction N((4)S,(2)D,(2)P)+SiH(4) in crossed molecular beams at a collision energy of 4.7 kcal mol(-1) with a time-of-flight mass spectrometer and selective photoionization. Ion signals were observed at m/z=42-45, associated with two product channels, HSiNH/SiNH(2)+H+H and HSiN/HNSi+H(2)+H. The species producing the signal at m/z=43 is assigned to product HSiN/HNSi and that at m/z=44 to product HSiNH/SiNH(2). The signal observed at m/z=42 is attributed to daughter ions of those two products and that at m/z=45 to (29)Si and (30)Si isotopic variants. We report time-of-flight spectra as a function of laboratory angle and simulations for the two products, from which both kinetic-energy and angular distributions of products in the center-of-mass (c.m.) frame were derived. The dependence of release of kinetic energy on the c.m. scattering angle is weak. The average translational energy released is 7.7 kcal mol(-1) for product channel HSiNH/SiNH(2)+H+H and 30.3 kcal mol(-1) for product channel HSiN/HNSi+H(2)+H. Through consecutive triple fragmentation, the angular distribution is slightly anisotropic for product HSiNH/SiNH(2) but isotropic for product HSiN/HNSi. Assuming equal efficiencies of detection, we estimate the branching ratios of products HSiNH/SiNH(2) and HSiN/HNSi to be roughly 15:85. To facilitate an understanding of the reaction mechanisms, we calculated the potential-energy surface for reaction N((2)D)+SiH(4) with quantum-chemical methods. Reactions N((2)D)+SiH(4)-->SiNH(2)+H+H and N((2)D)+SiH(4)-->HNSi+H(2)+H account satisfactorily for the present experimental results. Isomeric products HSiNH and HSiN are minor in this work.

We conducted the reaction C((3)P)+SiH(4) at a collision energy of 4.0 kcal mol(-1) in a crossed molecular-beam apparatus measuring time-of-flight mass spectra and selective photoionization. Product ions with m/z=41-43 are associated with two product channels, H(2)SiCH/HSiCH(2)/SiCH(3)+H and H(2)SiC/HSiCH/SiCH(2)+H(2). Apart from daughter ions and isotopic variants of reaction products, the species observed at m/z=43 is assigned to product H(2)SiCH/HSiCH(2)/SiCH(3) and that at m/z=42 to product H(2)SiC/HSiCH/SiCH(2). The signals observed at m/z=41 are due to dissociative ionization of silicon-carbon hydrides of these two types. We report time-of-flight spectra of products at specific laboratory angles and theoretical simulations, from which both kinetic-energy and angular distributions of products in the center-of-mass frame were derived. The release of kinetic energy is weakly dependent on the scattering angle for these two reactions. The channels for loss of H and H(2) release average translational energies of 10.5 and 16.7 kcal mol(-1), respectively. As hydrogen transfer before decomposition is facile, products H(2)SiCH/HSiCH(2)/SiCH(3) and H(2)SiC/HSiCH/SiCH(2) exhibit mildly forward/backward preferred and isotropic angular distributions, respectively. We estimate the branching ratios of these channels for loss of H and H(2) to be roughly 6:4. The measurements of release of kinetic energy and ionization thresholds of products indicate that SiCH(3)((2)A(")) and SiCH(2)((3)A(2)) are dominant among isomeric products. To explore the reaction mechanism, we computed the potential-energy surfaces for the reaction C((3)P)+SiH(4). The most likely mechanism is that atom C (3)P inserts into bond Si-H of SiH(4) in the entrance channel, and the reaction complex H(3)SiCH subsequently isomerizes to HSiCH(3) followed by decomposition to SiCH(3)((2)A("))+H and SiCH(2)((3)A(2))+H(2). We observed no significant evidence for the reaction C((1)D)+SiH(4).

To investigate the reactions of oxygen atoms with ethene and silane in a crossed-beam condition, we developed a stable, highly intense, and short-pulsed source of atomic oxygen with a transient high-voltage discharge. Mixtures of O(2) and He served as discharge media. Utilizing a crossed molecular-beam apparatus and direct vacuum-ultraviolet ionization, we measured the temporal profiles of oxygen atoms and the time-of-flight spectra of reaction products. With O(2) 3% seeded in He as a discharge medium, oxygen atoms might have a full width as small as 13.5 micros at half maximum at a location 193 mm downstream from the discharge region. Most population of oxygen atoms is in the ground state (3)P but some in the first excited state (1)D, depending on the concentration of precursor O(2). This discharge device analogously generates carbon, nitrogen, and fluorine atoms from precursors CO, N(2), and F(2), respectively.

Using photofragment translational spectroscopy and tunable vacuum-ultraviolet ionization, we measured the time-of-flight spectra of fragments upon photodissociation of vinyl fluoride (CH2CHF) at 157 and 193 nm. Four primary dissociation pathways--elimination of atomic F, atomic H, molecular HF, and molecular H2--are identified at 157 nm. Dissociation to C2H3 + F is first observed in the present work. Decomposition of internally hot C2H3 and C2H2F occurs spontaneously. The barrier heights of CH2CH --CHCH + H and cis-CHCHF --CHCH + F are evaluated to be 40+/-2 and 44+/-2 kcal mol(-1), respectively. The photoionization yield spectra indicate that the C2H3 and C2H2F radicals have ionization energies of 8.4+/-0.1 and 8.8+/-0.1 eV, respectively. Universal detection of photoproducts allowed us to determine the total branching ratios, distributions of kinetic energy, average kinetic energies, and fractions of translational energy release for all dissociation pathways of vinyl fluoride. In contrast, on optical excitation at 193 nm the C2H2 + HF channel dominates whereas the C2H3 + F channel is inactive. This reaction C2H3F --C2H2 + HF occurs on the ground surface of potential energy after excitation at both wavelengths of 193 and 157 nm, indicating that internal conversion from the photoexcited state to the electronic ground state of vinyl fluoride is efficient. We computed the electronic energies of products and the ionization energies of fluorovinyl radicals.