Formyl Fluoride Research Articles

Multiphoton ionization/dissociation dynamics of formyl fluoride by velocity mapping ion imaging

The dissociation dynamics of HFCO(+) ion has been studied using the velocity map ion imaging technique. The HFCO(+) ion is prepared by one-photon resonant three-photon ionization in the region of 43100-43860 cm(-1) excitation energy. The HFCO(+) ions, produced by multiphoton ionization, have sufficient internal energy to dissociate into the F and HCO(+) fragments without further absorption of another photon. Images of HCO(+) have been recorded at various excitation energies. It is noticed that the angular distributions of HCO(+) change dramatically from parallel distribution to perpendicular distribution and then back to parallel distribution in a very narrow excitation energy region of 43 473-43 500 cm(-1). Analysis of anisotropy parameters of beta(n) (n = 2, 4 and 6) reveals that the electronic states in the three-photon excitation of HFCO are mainly: HFCO(X(1)A') --> HFCO(A(1)A'') --> HFCO(A') --> HFCO(+)(A(2)A'';B(2)A'). The purely perpendicular resonant transitions are likely responsible for the perpendicular angular distribution of the HCO(+) ion fragment.

Infrared Multiphoton Dissociation Spectra as a Probe of Ion Molecule Reaction Mechanism: The Formation of the Protonated Water Dimer via Sequential Bimolecular Reactions with 1,1,3,3−Tetrafluorodimethyl Ether

The gas-phase ion-molecule reactions of 1,1,3,3-tetrafluorodimethyl ether and water have been examined using Fourier transform ion cyclotron resonance mass spectrometry, infrared multiphoton dissociation (IRMPD) spectroscopy, and ab initio molecular orbital calculations. This reaction sequence leads to the efficient bimolecular production of the proton-bound dimer of water (H5O2+). Evidence for the dominant mechanistic pathway involving the reaction of CF2H-O=CHF+, an ion of m/z 99, with water is presented. The primary channel occurs via nucleophilic attack of water on the ion of m/z 99 (CF2H-O=CHF+), to lose formyl fluoride and yield-protonated difluoromethanol (m/z 69). Association of a second water molecule with protonated difluoromethanol generates a reactive intermediate that decomposes via a 1,4-elimination to release hydrogen fluoride and yield the proton-bound dimer of water and formyl fluoride (m/z 67). Last, the elimination of formyl fluoride occurs by the association of a third water molecule to produce H5O2+ (m/z 37). The most probable isomeric forms of the ions with m/z 99 and 69 were found using IRMPD spectroscopy and electronic structure theory calculations. Thermochemical information for reactant, transition state, and product species was obtained using MP2(full)/6-311+G**//6-31G* level of theory.

A Spectroscopist's View of Energy States, Energy Transfers, and Chemical Reactions

This chapter describes a research career beginning at Berkeley in 1960, shortly after Sputnik and the invention of the laser. Following thesis work on vibrational spectroscopy and the chemical reactivity of small molecules, we studied vibrational energy transfers in my own lab. Collision-induced transfers among vibrations of a single molecule, from one molecule to another, and from vibration to rotation and translation were elucidated. My research group also studied the competition between vibrational relaxation and chemical reaction for potentially reactive collisions with one molecule vibrationally excited. Lasers were used to enrich isotopes by the excitation of a predissociative transition of a selected isotopomer. We also tested the hypotheses of transition-state theory for unimolecular reactions of ketene, formaldehyde, and formyl fluoride by (a) resolving individual molecular eigenstates above a dissociation threshold, (b) locating vibrational levels at the transition state, (c) observing quantum resonances in the barrier region for motion along a reaction coordinate, and (d) studying energy release to fragments.

Quantifying resonance through a Lewis Valence Bond approach: application to haloallyl and carbonylcations

A recent Valence Bond scheme based on Lewis structures, the VBB method (M. Linares, B. Braida and S. Humbel, J. Phys. Chem. A, 2006, 110, 2505 2509) is applied to resonance effect quantification. An accurate evaluation of this effect is provided by targeting pi interactions only, while all other factors remain constant. Valence Bond theory allows us to circumvent two main shortcomings of other approaches, i.e. the lack of a quantitative aspect, and the difficulty to properly separate resonance from other effects. The pi effect of fluorine and chlorine atoms is found to be comparable and quite significant (approximately 20 kcal mol(-1)), in both haloallyl and protonated carbonyl cations. The validity of the resonance model for carbonyl compounds is confirmed. Resonance in protonated formamide is indeed found to be significantly larger than in formic acids, itself being more resonant than the formyl fluoride cation. Comparisons with other methods of resonance effect evaluation are also made.

Structure and Matrix Isolation Infrared Spectrum of Formyl Fluoride Dimer: Blue-Shift of the C−H Stretching Frequency

Infrared spectroscopy (IR) of formyl fluoride (HCOF) dimer is studied in low-temperature argon and krypton matrixes. New IR absorptions, ca. 17 cm(-1) blue shifted from the monomer C-H stretching fundamental, are assigned to the HCOF dimer. The MP2/6-311++G calculations were utilized to define structures and harmonic frequencies of various HCOF dimers. Among the four optimized structures, the dimer having two C-H...O hydrogen bonds possesses strongest intermolecular bonding. The calculated harmonic frequencies of this dimer structure are shifted from the monomer similarly as observed in the experiment. Thus, we suggest that the experimentally observed blue shifted C-H bands belong to the dimer with two C-H...O hydrogen bonds. This observation includes the HCOF dimer to the class of hydrogen bonded complexes showing blue shift in their vibrational energies.

Photodissociation of Formyl Fluoride in Rare Gas Matrixes

Photodissociation of formyl fluoride (HCOF) is studied in Ar, Kr, and Xe matrixes at 248 and 193 nm excitation by following spectral changes in the infrared absorption spectra. In all matrixes, the main photodissociation products are CO/HF species, including CO-HF and OC-HF complexes and thermally unstable CO/HF species (a distorted CO/HF complex or a reaction intermediate), which indicate negligible cage exit of atoms produced via the C-F and C-H bond cleavage channels. However, the observation of traces of H, F, CO, CO(2), F(2)CO, FCO, and HRg(2)(+) (Rg = Kr or Xe) in Kr and Xe matrixes would imply some importance of other reaction channels too. The analysis of the decay curves of the precursor shows that dissociation efficiency of HCOF increases as Ar < Kr < Xe, the difference being the factor of 10 between Ar and Xe. Moreover, HCOF dissociates 20-50 times faster at 193 nm compared to 248 nm. Interestingly, whereas the CO/HF species are stable with respect to photolysis in Ar, they photobleach in Kr and Xe matrixes at 248 and 193 nm, even though the first excited states of CO and HF are not energetically accessible with 193 and 248 nm photons. In krypton matrix, the photodissociation of CO/HF species at 248 nm is observed to be a single photon process. Quantum chemical calculations of electronic excitation energies of CO-HF and OC-HF complexes show that the electronic states of HF and CO mostly retain their diatomic nature in the pair. This clearly demonstrates that photodissociation of CO/HF complexes is promoted by the surrounding rare gas lattice.

Photodissociation dynamics of formyl fluoride (HFCO) at 193 nm: Branching ratios and distributions of kinetic energy

Following photodissociation of formyl fluoride (HFCO) at 193 nm, we detected products with fragmentation translational spectroscopy utilizing a tunable vacuum ultraviolet beam from a synchrotron for ionization. Among three primary dissociation channels observed in this work, the F-elimination channel HFCO-->HCO+F dominates, with a branching ratio approximately 0.66 and an average release of kinetic energy approximately 55 kJ mol(-1); about 17% of HCO further decomposes to H+CO. The H-elimination channel HFCO-->FCO+H has a branching ratio approximately 0.28 and an average release of kinetic energy approximately 99 kJ mol(-1); about 21% of FCO further decomposes to F+CO. The F-elimination channel likely proceeds via the S1 surface whereas the H-elimination channel proceeds via the T1 surface; both channels exhibit moderate barriers for dissociation. The molecular HF-elimination channel HFCO-->HF+CO, correlating with the ground electronic surface, has a branching ratio of only approximately 0.06; the average translational release of 93 kJ mol(-1), approximately 15% of available energy, implies that the fragments are highly internally excited. Detailed mechanisms of photodissociation are discussed.

Ozonolysis of Fluoroethene: Theoretical Study of Unimolecular Decomposition Paths of Primary and Secondary Fluorozonide

A theoretical investigation into unimolecular decomposition paths of primary (POZF) and secondary (SOZF) fluorozonide was carried out by utilizing the multiconfigurational CASSCF/cc-pVTZ level in optimizations of the stationary points and calculations of the harmonic vibrational frequencies. The dynamical electron correlation was accounted for via the multireference CASPT2/cc-pVTZ treatment based on the zeroth-order CASSCF/cc-pVTZ reference. The CASPT2 was substituted with the CCSD(T)/6-311G(2d,2p) correction whenever the former resulted in negative activation barriers. The most favorable decomposition route of POZF is a concerted cleavage to carbonyl oxide (CO) and formyl fluoride (FF) with fragments in the anti conformation, with regard to the orientation of the terminal oxygen in the carbonyl oxide and the flourine atom of the carbonyl compound. The ratio of unimolecular rate constants calculated within the RRKM formalism suggests that the CO-FF channel of cleavage amounts to 98%, which agrees well with the upper bound of experimental esimates. The SOZF decomposition most readily takes place in a stepwise manner initiated by the O-O bond rupture. Two conformational minima are exhibited by SOZF, the O-O and H(2)C-O half-chairs. The calculated rotational constants and scaled frequencies for the O-O half-chair are in good agreement with the experimental values.

Unimolecular Dissociation of Formyl Halides HXCO → CO + HX (X= F, Cl): An Ab Initio Direct Classical Trajectory Study

The dynamics of the unimolecular dissociation of formyl halides, HXCO (X = F, Cl), have been studied by classical trajectory calculations at the MP2/6-31G(d,p) level of theory and have been compared to similar calculations for H2CO. The calculated transition states are planar with elongated C−X and H−X bonds. Trajectories were started from the transition state with 12 kcal/mol of energy above the potential barrier, corresponding to the zero-point energy plus 2.25 and 2.87 kcal/mol of excess energy in the transition vector of formyl fluoride and formyl chloride, respectively. The CO fragments are produced rotationally hot with 〈J〉 = 40−50 but vibrationally cold with only 10−20% in v = 1. The HX fragment shows significant vibrational excitation with 〈v〉 = 1.0 for HF and 〈v〉 = 2.3 for HCl, compared to 〈v〉 = 1.16 for H2. The average rotational quantum number for HCl, 〈J〉 = 12.8, is considerably higher than for HF, 〈J〉 = 9.5, or H2, 〈J〉 = 3.3. Product translation receives about 42% of the available energy in formyl fluoride and about 31% in formyl chloride compared to 70% for formaldehyde. The results show good qualitative agreement with the available experimental energy partitioning for HFCO; HF is observed to be vibrationally hot, but the distribution has not been measured. No experiments are available for HClCO dissociation.

Ab initio studies of dissociation pathways on the ground- and excited-state potential energy surfaces for formyl chloride (HClCO)

Potential energy surfaces of the HClCO dissociation to H+ClCO and Cl+HCO in the lowest three electronic states (S0, S1, and T1) have been investigated with ab initio molecular orbital method at the levels of the complete active space self-consistent-field, single- and multi-reference MP2. The results show that the C–Cl bond cleavage on the S1 surface is the most probable mechanism for the HClCO photodissociation at 230–320 nm. In comparison with formyl fluoride (HFCO), a significant difference was found in photodissociation dynamics between HClCO and HFCO, and this has been discussed in detail.

Characterization of ν3 Vibrational Levels in S0 Formyl Fluoride Using Dispersed Fluorescence Spectroscopy

The harmonic frequency and anharmonic constants of the CH bend (ν3) of formyl fluoride (HFCO) have been determined using the technique of dispersed fluorescence spectroscopy. Sample molecules were cooled in a supersonic expansion and excited to low J′, Ka′=0 rotational states in the 31 vibrational level of S1 HFCO. The resulting fluorescence to the ground electronic state was dispersed and a 23 000 cm−1 pure vibrational spectrum was recorded. A total of 142 new vibrational assignments were made, which extends the total number of vibrational assignments for S0 HFCO to 382. Of these assignments, 109 involve ν3 with v3=1–2. The data were analyzed using a multiresonant Hamiltonian model, which accounts for resonant interactions among nearly degenerate states, with a standard deviation of 4.5 cm−1.

Dispersed Fluorescence Spectroscopy of S0 Formyl Fluoride Vibrational States

Dispersed fluorescence (DF) spectroscopy was used to record a 22 500 cm-1 spectrum of the vibrational energy levels of formyl fluoride (HFCO) and thereby determine harmonic frequencies and anharmonic constants for the S0 potential energy surface. Sample molecules were cooled in a supersonic expansion and excited to low J, Ka = 0 rotational states in the 62 vibrational level of S1 HFCO, and the resulting fluorescence was dispersed from 255 to 600 nm. Long progressions in the CO stretch (υ2 = 0−6) and out-of-plane bend (υ6 = 0−23) and shorter progressions in the CF stretch (υ4 = 0−2) and FCO bend (υ5 = 0−2) are observed. Analysis of the spectrum results in 240 assignments, including 196 new assignments and 56 assignments above the approximate 17 000 cm-1 dissociation threshold. The data are fit to an anharmonic oscillator model with a standard deviation of 3.3 cm-1.

Equilibrium C−F Bond Length and the Structure of Formyl Fluoride, Difluorocarbene, Monofluoromethylene, and Difluoromethane

Highly correlated ab initio calculations with large basis sets are reported for formyl fluoride, OCHF; difluorocarbene, CF2; monofluoromethylene, CHF, and difluoromethane, CH2F2. Based on CCSD(T)/cc-pVQZ results (including a correction for the effect of diffuse functions on fluorine and oxygen), equilibrium structures are derived. These structures are compared to experimental results, when available, and to those of similar molecules; and their accuracy is discussed.

Rotational structure in the Ã1A″–X̃1A′ spectrum of formyl chloride

High-resolution cavity ring-down spectroscopy has been used to record three vibronic bands of the A1A″–1A′ (π*â†�nO) transition of room-temperature formyl chloride (HClCO). These three bands (601, 501601 and 201501601) are all vibronically induced through the activity of the out-of-plane inversion vibration ν6, and are found to obey type-a selection rules. Rotational constants have been derived from the analysis of these bands and used to give information on the geometrical structure of the excited state. The properties of the Astate are found to be intermediate between those of the corresponding states of formaldehyde and formyl fluoride.

Ultraviolet photolysis of formyl fluoride: the F+HCO product channel

The time-of-flight spectrum of the H atoms resulting from photodissociation of gas phase HFCO molecules at 243.12 nm indicates a role for secondary photolysis of HCO() fragments arising via the F+HCO() dissociation channel. Analysis of this spectrum, and of earlier photofragment translational spectroscopy results obtained at a number of neighbouring wavelengths in the range 218.4–248.2 nm, allow estimation of an upper limit for the C–F bond dissociation energy: D0(F–CHO)⩽482 kJ mol-1. HCO() fragments are deduced to be amongst the primary products of HFCO photolysis at all wavelengths λ⩽248.2 nm, indicating that any energy barrier in the F–C bond fission channel [measured relative to the asymptotic products F(2P)+HCO()] must be small. This observation is considered in the light of available knowledge regarding the potential energy surfaces for the ground (1A′) and first excited singlet (A1A″) and triplet (a3A″) states of HFCO; the available evidence all points to radiationless transfer and subsequent dissociation on the triplet surface as the mechanism for the deduced F–C bond fission.

Hydrogen radical and hydroxyl radical hydrogen abstraction reaction from formyl fluoride studied with hybrid density functional theory methods

With the goal of reducing flame velocity in combustion reactions, this study focused on the conversion of hydrogen and hydroxyl radicals into relatively unreactive hydrogen and water molecules through the inter-conversion of formyl fluoride to fluoroformyl radicals. Hybrid DFT computational methods were employed to confirm these results. Based on this, the fluoroformyl radical-assisted transformation of the hydrogen and hydroxyl radicals into hydrogen and water molecules was discussed.

Spectroscopic Observation of the Formyl Cation in a Condensed Phase

The formyl cation, HCO+, has long been believed to be an important intermediate in the chemistry of carbon monoxide (CO) in acidic environments, but its spectroscopic observation in solution has been elusive. This species was generated by the reaction of CO with the liquid superacid hydrofluoric acid-antimony pentafluoride (HF-SbF5) under pressure and was observed by nuclear magnetic resonance and infrared spectroscopy. Equilibria between CO in the gas phase, CO dissolved in HF-SbF5, the SbF5 adduct of formyl fluoride, and HCO+ associated with several equilibrating anions of the type [SbxF5x+1]- are proposed to describe the system.

A High-Level Computational Study on the Thermochemistry of Vinyl and Formyl Halides: Heats of Formation, Dissociation Energies, and Stabilization Energies

The heats of formation, ΔHf 298, of vinyl and formyl halides calculated using G2 theory are −145.9 (CH2CHF), 21.8 (CH2CHCl), 79.6 (CH2CHBr), 147.1 (CH2CHI), −393.7 (HFCO), −192.7 (HClCO), −133.9 (HBrCO), and −66.2 kJ mol-1 (HICO), which agree with the available experimental data. While the covalent radii of sp3 and sp2 hybridized carbons are 0.762 and 0.735 Å, respectively, at the MP2/6-31G(d) level, the C−X bond lengths in formyl bromide and iodide are 0.016 and 0.045 Å, respectively, longer when compared with those in methyl bromide and iodide. However, the C−F bond in formyl fluoride is 0.040 Å shorter than the C−F bond in methyl fluoride. The C−X bond dissociation energies (DC-X) for vinyl, formyl, and methyl halides show good linear correlations with the Mulliken and Pauling electronegativites of the halogens. The DC-X values for formyl bromide and iodide are smaller than those calculated for methyl bromide and iodide. The stabilization energies (SE) yielding estimates of the stabilization of the CC and CO double bonds by halogens decrease from X = F to X = I and show reasonable linear correlations with the Mulliken and Pauling electronegativities of the halogens. While the DC-X energies for formyl halides are smaller than those for vinyl halides, the SE(formyl) values are larger than the corresponding SE(vinyl). The elimination of HX from formyl halides is exothermic, in contrast to the endothermic elimination of HX from vinyl halides.

Vibrational Assignment of theS1Fluorescence Excitation Spectrum of Formyl Fluoride

TheS1fluorescence excitation spectrum of jet-cooled formyl fluoride, HFCO and DFCO, was recorded from 37500 to 40250 cm−1at 0.20 cm−1resolution. Vibrational bands were assigned primarily to progressions in the Franck–Condon active modes ν2, ν5, and ν6. Tunneling splittings were observed in the ν6progression and fit to a model double-well potential Hamiltonian. Vibrational energies were fit to a Dunham expansion modified to account for the inversion doubling in the ν6progression. Best fit spectroscopic constants are reported including harmonic frequencies and anharmonic constants.S0→ S1Franck–Condon factors were calculated with the Duschinsky rotation included and support the vibrational assignment. TheS1geometry and vibrational potential inferred from the present analysis are compared toab initioresults.

An in situ IR study of the thermal decomposition of trifluoroacetic acid

The pyrolysis of trifluoroacetic acid has been carried out in the temperature range 513–593 K both as the neat gas and also in the presence of nitrogen as diluent. Reactions were carried out in a sealed sodium borosilicate glass cell, and the progress of the reaction was monitored by in situ Fourier transform IR spectroscopy. The principal products are CHF3, CF3COF and CO2, but significant amounts of other species including C2F4, CO and SiF4 are also produced. The formation of HF is observed directly for the first time for this reaction as is the formation of a number of other minor species (formaldehyde, formyl fluoride and hexafluoropropylene oxide).