High-Accuracy Theoretical Study on the Thermochemistry of Several

Nov 16, 2010 - Department of Applied and Environmental Chemistry, University of Szeged, Rerrich B. tér 1., H-6720 Szeged, and Department of Physical ...
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J. Phys. Chem. A 2010, 114, 13213–13221

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High-Accuracy Theoretical Study on the Thermochemistry of Several Formaldehyde Derivatives Bala´zs Nagy,*,†,‡ Jo´zsef Csontos,‡ Miha´ly Ka´llay,‡ and Gyula Tasi† Department of Applied and EnVironmental Chemistry, UniVersity of Szeged, Rerrich B. te´r 1., H-6720 Szeged, and Department of Physical Chemistry and Materials Science, Budapest UniVersity of Technology and Economics, P.O. Box 91, H-1521 Budapest, Hungary ReceiVed: September 7, 2010; ReVised Manuscript ReceiVed: October 26, 2010

In the case of several formaldehyde derivatives, with importance in atmospheric and combustion chemistry, the currently available thermochemical values suffer from considerably large uncertainties. In this study a high-accuracy theoretical model chemistry has been used to provide accurate thermochemical data including heats of formation at 0 and 298 K and standard molar entropies at 298 K for CF2O, FCO, HFCO, HClCO, FClCO, HOCO, and NH2CO. For most of the thermochemical quantities studied here, this investigation delivers the best available estimate. Introduction Formaldehyde derivatives have been implicated in a number of important atmospheric processes including the photo-oxidation1-4 of hydrofluorocarbons, fluorocarbons, and chlorofluorocarbons, as well as of carbon monoxide. Since they play a significant role in atmospheric as well as in combustion chemistry, the accurate knowledge of their thermochemical properties is highly desirable. However, the tightest uncertainties associated with the thermochemical values of some formaldehyde derivatives listed in wellestablished compilations such as NIST-JANAF,5 JPL,6 and the Third Millennium Ideal Gas and Condensed Phase Thermochemical Database for Combustion7 are considerably large, and in some cases even discrepancies can be found among the databases. The experimental investigation of open-shell radical systems and highly reactive closed-shell species requires elaborate work, and usually it is cumbersome and time-consuming. On the other hand, computational chemistry has emerged as a reliable and safe tool for determining the thermochemical properties of small molecules accurately including highly reactive species as well. The so-called theoretical model chemistries were pioneered by Petersson and his associates,8-12 as well as by Pople and his associates,13-16 and were specifically designed to reach chemical or even better accuracy in thermochemical applications. Since then, several model chemistries17-26 have been developed to deliver more reliable and more accurate thermochemical data. The high-accuracy extrapolated ab initio thermochemistry (HEAT) protocols24-26 belong to the most accurate, and consequently most time-consuming, family of model chemistries. These protocols are based on the coupled-cluster singlet, doublet, and perturbative triplet [CCSD(T)] method and feature corrections due to (i) iterative triple and perturbative quadruple excitations in coupled-cluster theory, (ii) the deficiency of the Born-Oppenheimer approximation, and (iii) relativistic effects. Furthermore, no empirical corrections are applied, and for heat of formation values the prestigious (1 kJ/mol accuracy range is the goal. * To whom correspondence should be addressed: E-mail: n.balazs@ chem.u-szeged.hu. † University of Szeged. ‡ Budapest University of Technology and Economics.

Two of the authors of the present paper (B.N. and G.T.) were involved in a recent work27 on the heat of formation and proton affinity of the parent formaldehyde molecule, and with the help of quantum chemical computations more accurate data were obtained than those provided by previous theoretical and experimental studies. The focus of this study is on the derivatives of formaldehyde, and a slightly modified HEAT II25 protocol is used to provide accurate heats of formation and molar entropies for several atmospherically important species including CF2O, FCO, HFCO, HClCO, FClCO, cis- and trans- HOCO, and NH2CO. The results obtained are discussed thoroughly and compared to previous theoretical as well as experimental data available in databases and in the literature. Methods A HEAT345-(Q) model chemistry25 was applied to calculate the total energies of atoms and molecules investigated in this study. Coupled-cluster (CC) theory28 up to the perturbative treatment of quadruples, CCSDT(Q),29 with the correlation-consistent basis set families of Dunning30-33 was used to calculate the total electronic energies. In all calculations the restricted and unrestricted Hartree-Fock orbitals were used for closed- and open-shell systems, respectively. In the correlation calculations all electrons were correlated except in the CCSDT34,35 and CCSDT(Q)29 computations, where the frozen-core approximation was applied. The reference structures of the molecules were obtained from CCSD(T)36 optimizations using the cc-pVQZ basis set. It was demonstrated that this level of theory provides highly accurate geometries,37 and it was also validated in several thermochemical studies including the HEAT project.24 The additivity of the various contributions to the total energy was assumed according to the following scheme: ∞ ∞ ∞ ETOT ) EHF + ∆ECCSD(T) + ∆ECCSDT + ∆ECCSDT(Q) + ∆EZPE + ∆EDBOC + ∆EREL (1) ∞ In eq 1 EHF is the basis set limit HF-SCF energy obtained by extrapolating the aug-cc-pCVXZ (X ) T, Q, 5) energies using ∞ contribution the three-point formula of Feller.38 The ∆ECCSD(T)

10.1021/jp1085203  2010 American Chemical Society Published on Web 11/16/2010

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Nagy et al.

TABLE 1: Contributions to the Enthalpies of Formation (kJ/mol) at 0 K for the Species Studied in This Work ∆EZPE species

∞ EHF

∞ ∆ECCSD(T)

∞ ∆ECCSDT

∆ECCSDT(Q)

∆EREL

harm

CF2O FCO HFCO HClCO FClCO cis-HOCO trans-HOCO NH2CO

-550.01 -151.76 -329.41 -143.51 -347.91 -140.95 -145.71 -5.88

-68.78 -28.85 -62.66 -44.04 -70.75 -40.49 -42.77 -1.85

0.94 0.16 0.54 0.33 0.84 0.23 0.23 0.00

0.91 0.09 0.28 -0.10 0.25 0.09 0.08 0.01

1.24 0.33 0.68 0.32 0.83 0.36 0.37 0.02

12.46 2.83 11.97 6.25 8.48 6.29 6.65 0.49

a

a

anharmb

∆EDBOC

total

-0.05 -0.02 -0.14 -0.07 -0.04 -0.12 -0.12 0.00

-0.08 -0.01 -0.03 -0.01 -0.05 -0.04 -0.05 0.00

-603.37 -177.24 -378.77 -180.82 -408.35 -174.63 -181.32 -7.21

Harmonic contributions to ∆EZPE. b Anharmonic contributions to ∆EZPE.

is the correlation energy extrapolated by the two-point formula of Helgaker et al.39 using the aug-cc-pCVXZ (X ) Q, 5) basis sets. The same formula is used to evaluate ∆E∞CCSDT, which was defined by extrapolating the difference between the CCSDT and CCSD(T) energies to the basis set limit using the cc-pVTZ and cc-pVQZ basis sets. The effect of quadruple excitations in CC theory was taken into account utilizing CCSDT(Q) computations, and it was quantified as ∆ECCSDT(Q) ) ECCSDT(Q) - ECCSDT using the cc-pVDZ basis set. The zero-point vibrational energy, ∆EZPE, is calculated relying on vibrational perturbation theory.40 Harmonic frequencies and anharmonicity corrections were determined at the CCSD(T)/ccpVQZ level of theory. For harmonic frequencies analytic secondderivative techniques were used,41,42 while anharmonicity corrections were taken from cubic force fields obtained by numerical differentiation of analytic second derivatives.25,43 In eq 1 the term ∆EDBOC is the energy associated with the diagonal Born-Oppenheimer correction. This contribution was calculated at the CCSD level of theory with the aug-cc-pCVTZ basis set using the formalism of Gauss et al.44 The relativistic contributions, ∆EREL in eq 1, were taken into account by evaluating the expectation value of the mass-velocity and oneand two-electron Darwin operators at the CCSD(T)/aug-cc-pCVTZ level of theory. For the carbon atom the energy lowering of the lowest spin-orbit state with respect to the energy evaluated within a nonrelativistic approximation was also considered. This contribution, -0.000135 Eh, was calculated from the experimental fine-structure splittings available in the NIST Atomic Spectra Database.45 From the calculated total energies, harmonic frequencies, and rotational constants, standard enthalpies and entropies were calculated at T ) 0 and 298.15 K at a pressure of 1 bar via the standard formulas of statistical thermodynamics within the ideal gas approximation.46 It was further assumed that the excited states of the molecules studied here lie far above the ground states; therefore, the electronic contribution to the molecular partition function was set to zero. To obtain the heats of formation from the calculated enthalpies, the elemental reaction approach was used.24 For instance, the heat of formation for FClCO was calculated on the basis of the following equations:

1 1 1 F + Cl2 + O2 + C ) FClCO 2 2 2 2 1 )) H°(FClCO) - H°(C ∆fH°(FClCO) T T T gas) - H°(F 2 T 2 1 1 ) + ∆fH°(C H°(Cl ) - H°(O T gas) 2 T 2 2 T 2 The reference states of the elements were defined as is standard in thermochemistry except for carbon, where the gaseous carbon

atom was used as a reference state. For the heat of formation of the carbon atom at 0 K, ∆fH°(C 0 gas), the ab initio value of ref 47, 711.65 ( 0.32 kJ/mol, was adopted. To calculate the heat of formation at 298.15 K, the thermal corrections, ∆fH°298 ∆fH°, 0 were obtained from the NIST-JANAF tables, resulting in ∆fH°298(Cgas) ) 717.13 ( 0.32 kJ/mol. The errors introduced by the protocol used in this study were investigated thoroughly in ref 48. The benchmark set contained 26 molecules for which accurate experimental heat of formation data were available; 17 first-row species were included from the original HEAT test set, and another 9 chlorine-containing compounds were obtained from experimental databases. For first-row species the root-mean-square (rms) deviation was 0.39 kJ/mol with a maximum error of 0.72 kJ/mol; the corresponding measures of error for the chlorine-containing molecules were 0.41 and 0.58 kJ/mol. To give a size-dependent error estimate for the heat of formation values, the rms deviations were calculated on a per-atom basis, and 0.16 and 0.41 kJ/mol were obtained for first-row and chlorine atoms, respectively. Therefore, for a given molecule the 95% confidence limit was estimated as twice the above rms values; i.e., for every firstrow atom and for a chlorine atom, uncertainties of 0.3 and 0.8 kJ/mol, respectively, are considered, and these contributions are summed. For instance, in the case of HClCO the error bar for the ∆fH°T values is 0.3 kJ/mol + 0.8 kJ/mol + 0.3 kJ/mol + 0.3 kJ/mol ) 1.7 kJ/mol. On the basis of a statistical analysis of a benchmark set of 15 methane derivatives including radicals, the current protocol yielded an rms deviation of 0.6 J/(K · mol); therefore, our conservative estimate is 1.5 J/(K · mol) for the error associated with our entropy data. CCSDT(Q) calculations were performed with the MRCC suite of programs49 interfaced to the CFOUR package, while all other calculations were carried out with CFOUR.51 Results and Discussion Most of the quantum chemical methods benefit from some error cancellation, and whether one can rely on error cancellation and to what extent is an important question in the field of computational thermochemistry. Table 1 contains the contributions of the considered factors to the total enthalpies of formation at 0 K. It can be seen that the effect of DBOC is the least significant, and therefore, it can be safely neglected unless the target accuracy range is (0.1 kJ/mol. If the desired accuracy range is about (1.0 kJ/mol, the rest of the contributions must be taken into consideration. It is notable that the effects of iterative triple and perturbative quadruple excitations, as well as the relativistic corrections, are in roughly the same range. The importance of quadruple excitations for fluorine-containing and second-row compounds was pointed out by Martin and associates.52 It was found that, to reach a sub-kJ/mol accuracy range, the calculation of the (Q) contribution requires a better

Thermochemistry of Several Formaldehyde Derivatives

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TABLE 2: Temperature Corrections, Heats of Formation (in kJ/mol), and Total Molar Entropies (J/(K · mol)) for the Species Studied in This Work heats of formation species

H°298 - H°0

∆fH°0

∆fH°298

entropy

CF2O FCO HFCO HClCO FClCO cis-HOCO trans-HOCO NH2CO C H2 O2 F2 Cl2 N2

11.1 10.4 10.4 11.0 11.9 10.9 10.9 12.5 6.5 8.7 8.7 8.8 9.2 8.7

-603.4 -177.2 -378.8 -180.8 -408.4 -174.6 -181.3 -7.2

-606.5 -176.7 -382.5 -184.2 -410.9 -177.8 -184.5 -13.1

258.6 248.8 246.5 258.7 276.4 251.7 251.4 256.5 158.1 130.4 195.9 202.6 222.8 191.6

than double-ζ-quality basis set. To test the accuracy of our CCSDT(Q) contributions to the heats of formation, we recalculated them with the cc-pVTZ basis set for all species but FClCO. In line with the observations of Martin and associates the largest deviation was obtained with fluorine- and chlorinecontaining compounds, CF2O (0.4 kJ/mol), HFCO (0.2 kJ/mol), and HClCO (0.1 kJ/mol). For the other species the difference between the cc-pVDZ and cc-pVTZ results is negligible (see the Supporting Information). Therefore, the CCSDT(Q)/ccpVDZ level seems adequate considering our targeted accuracy. In most cases, as can be observed in Table 1, the effects of anharmonicity can be safely ignored unless very high accuracy is required. Nevertheless, for HFCO and for the HOCO isomers the contributions due to anharmonicity are relatively large, -0.14 and -0.12 kJ/mol, respectively. In the following section the relevant thermochemical data of each molecule will be discussed. The temperature corrections, heats of formation at 0 and 298.15 K, and standard molar entropy values calculated in this study are summarized in Table 2, while the best available values for the various thermodynamic functions can be found in Table 3. Thermochemical Data. CF2O. Three experimental investigations on the heat of formation of CF2O are discussed in the NIST-JANAF database.5 First, the early results of Ruff and Li53 on the equilibrium constant of the reaction 2CF2O h CO2 + CF4 were used by Stull et al.54 to calculate the reaction enthalpy, ∆rH°298 ) -50.2 ( 12.6 kJ/mol. Combining this value with the appropriate heats of formation of CO2 and CF4, ∆fH°298(CF2O) ) -638.1 ( 13.8 kJ/mol can be obtained. Second, Wartenberg and Riteris55 measured the enthalpy of hydrolysis of CF2O and calculated ∆fH°298(CF2O) ) -638.9 ( 1.7 kJ/mol. Third, the enthalpies of combustion of methane in O2/F2 mixtures were

investigated by Armstrong and associates,56 and they reported a somewhat lower value, -647.7 kJ/mol, for ∆fH°298(CF2O). On the basis of the detailed analysis of available experimental data, Stull and associates54 recommended ∆fH°298(CF2O) ) -641.0 ( 0.8 kJ/mol by giving the largest weight to the calorimetric value of Wartenberg and Riteris.55 A similar value, ∆fH°298(CF2O) ) -640.6 ( 5.9 kJ/mol, was determined by Amphlett and co-workers57 in an attempt to improve on the results of Ruff and Li.53 In 1994, several computational studies appeared, namely, those of Nyden and associates,58 Montgomery and associates,59 and Schneider and Wallington,60 which yielded much higher, less stable, ∆fH°(CF2O) data. The MP4 method with empirical bond additivity corrections (BACs)58 and G214 and CBS-QCI59 methods gave -598.3, -605.0 ( 5.1, and -609.6 ( 4.2 kJ/ mol for ∆fH°298(CF2O), respectively. On the basis of the work of Montgomery and associates,59 and a modified version of the G2(MP2) method,61 Schneider and Wallington60 recommended -607.9 ( 7.1 kJ/mol for ∆fH°298(CF2O). Because of the large, about 30 kJ/mol, discrepancies between the computed and measured values, these studies suggested the re-evaluation of available experimental data. Buckley and associates62 studied the photoionization mass spectra of CF2O and FCO and utilized the results to obtain the heats of formation of FCO and FCO+. They combined their experimental results with those computed by Schneider and Wallington.60 It was concluded that, on the basis of mutually consistent data, “the relative heats of formation of CF2O, FCO, and FCO+ are firmly established”. However, the accurate absolute values remained unconfirmed; therefore, it was suggested that the computed results should be verified by experiments. In an attempt to resolve the controversy surrounding the heat of formation of CF2O, Ruscic and associates63 conducted another photoionization mass spectrometry study and got a lower limit, +5.9 kJ/mol. They concluded that the ∆fH°298(CF2O) g -623.8-2.9 experimental values are indeed too low by about 15 kJ/mol and the computed values are probably too high by about the same amount. However, they noted that due to the nature of their experiment the computed values cannot be ruled out with certainty, and additional experiments and computations are needed to resolve the discrepancies. Nevertheless, the JPL database6 adopted this value. It should be noted here that Burcat’s compilation7 lists both Gurvich’s,64 -640.0 ( 5 kJ/ mol, and Ruscic’s ATcT value of -640.1 ( 1.1 kJ/mol for ∆fH°298(CF2O). Both of them disagree with the aforementioned photoionization study. Since then no experimental measurement has been performed to determine the heat of formation of CF2O. Nevertheless, several computational studies, applying more and more accurate methods, have been published.22,65-70 Feller and Dixon65 carried

TABLE 3: Best Available Heats of Formation at 0 and 298.15 K (kJ/mol) as Well as Standard Molar Entropies at 298.15 K (J/(K · mol)) for the Species Studied in This Worka

a

species

∆fH°0

∆fH°298

S°298

source

CF2O FCO HFCO HClCO FClCO cis-HOCO trans-HOCO NH2CO

-603.4 ( 1.2 -177.2 ( 0.9 -378.8 ( 1.2 -180.8 ( 1.7 -408.4 ( 1.7 -174.6 ( 1.2 -181.3 ( 1.2 -7.2 ( 1.5

-606.5 ( 1.2 -176.7 ( 0.9 -382.5 ( 1.2 -184.2 ( 1.7 -410.9 ( 1.7 -177.8 ( 1.2 -184.5 ( 1.2 -13.1 ( 1.5

258.9 ( 0.1 248.8 ( 1.5 246.5 ( 0.8 259.1 ( 0.2 276.7 ( 0.2 251.7 ( 1.5 251.4 ( 1.5 256.5 ( 1.5

this work; S, ref 5 this work this work; S, ref 5 this work; S, ref 64 this work; S, ref 64 this work this work this work

Adopted values are set as italic.

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out CCSD(T) calculations with the aug-cc-pV(D,T,Q)Z basis sets extrapolated to the basis set limit. Corrections for core-valence correlation and spin-orbit splittings were also considered. On the basis of the isodesmic CH2O + CF2H2f CF2O + CH4 reaction and the atomization energy approach, they recommended -607.5 ( 3.4 kJ/mol for ∆fH°(CF 0 2O), which considerably differs from the experimental values. G3 theory15 provides -609.6 kJ/mol for ∆fH°298(CF2O).67 With the 6-31G(d,p) basis set the BAC-MP2 method and MP2 method with atom additivity corrections (AACs) yielded -616.3 and -609.5 kJ/ mol, respectively, for ∆fH°298(CF2O).68 Kondo and associates68 also used their empirical corrections in the G2 and G2(MP2) composite approaches; the use of the AAC-G2 and AAC-G2(MP2) methods resulted in -606.8 and -606.3 kJ/mol for ∆fH°298(CF2O). With a more accurate version of the protocol used in ref 65, Dixon and associates investigated some of the thermochemical parameters, including ionization potentials (IPs) and heats of formations, of CHFO and CF2O.69 The most notable improvement in the applied protocol is the introduction of scalar relativistic corrections. The computations resulted in ∆fH°(CF 0 2O) ) -602.1 ( 4.2 kJ/mol and ∆fH°298(CF2O) ) -605.4 ( 4.2 kJ/mol.69 ∆fH°(CF 0 2O) is in line, within the given error bars, with their previously recommended value of -607.5 ( 3.4 kJ/mol.65 Due to the good agreement between their calculated IPs and those determined by experimental methods, they assumed that a systematic error exists in photoionization measurements.63 Bakowies also investigated the heat of formation of CF2O70 using another composite approach termed the ATOMIC71 protocol, which uses simple precomputed isodesmic corrections to estimate the contributions beyond CCSD(T). The most accurate version of the ATOMIC protocol yielded -606.7 ( 8.8 kJ/mol for ∆fH°298(CF2O). In an extensive study Feller, Peterson, and Dixon22 surveyed several factors which are needed to predict atomization energies accurately and also calculated the heat of formation for several molecules including CF2O. Briefly, in the case of CF2O their composite method consisted of (i) CCSD(T)/aug-cc-pV(5,6)Z extrapolation to assess the correlation of valence electrons, (ii) CCSD(T)/ccpCVQZ computation to estimate the core-core and core-valence contributions to the correlation energy, (iii) determination of the effect of higher excitations on the valence correlation energy, i.e., CCSDT/cc-pVTZ, CCSDT(Q)/cc-pVDZ, and estimated FCI/cc-pVDZ contributions, (iv) scalar relativistic corrections being obtained at the second-order Douglas-Kroll-Hess CCSD(T)/cc-pVTZ_DK level, and (v) computation of the harmonic and anharmonic contributions to the zero-point energy, respectively, at the CCSD(T)/aug-cc-pVTZ and CCSD(T)/aug-ccpVDZ levels. Their composite approach yielded -607.1 ( 2.1 kJ/mol for ∆fH°298(CF2O). Our protocol provides ∆fH°298(CF2O) ) -606.5 ( 1.2 kJ/ mol and ∆fH°(CF 0 2O) ) -603.4 ( 1.2 kJ/mol. The protocol used by Feller and associates in ref 22 is very similar to ours, and consequently, the data agree within the given error bars. However, a few contributions are calculated more accurately here. A statistical analysis performed in ref 48 suggested that using the cc-pVTZ basis set instead of cc-pV(T,Q)Z extrapolation in the calculation of the CCSDT contribution can cause an error of a few tenths of a kJ/mol in the heats of formation. The other notable differences in the protocols [(i) considering the harmonic and anharmonic contributions to the ZPE, respectively, in triple- and double-ζ basis sets and (ii) estimating the core-core, core-valence, and valence-valence correlation energies from different series of basis sets] can also introduce an error on the order of a few tenths of a kJ/mol in the value

Nagy et al. reported in ref 22. On the other hand, it was demonstrated that the difference between the cc-pV(4,5)Z and cc-pV(5,6)Z extrapolations is less than 0.1 kJ/mol,26 and it was also shown that the use of CCSDT(Q) instead of CCSDTQ changes the statistical measures of error by much less than 0.1 kJ/mol.25 On the basis of the recommendations given in the cited experimental works, ∆fH°298(CF2O) lies between -647.7 and -623.8 kJ/mol. However, we recall that the value of -623.8 kJ/mol is actually a lower limit63 for ∆fH°298(CF2O) and ∆fH°298(CF2O) should be greater than -623.8 kJ/mol. On the other hand, high-level calculations, which have been proven to be very successful in predicting heats of formation for similar systems, are fairly consistent. Therefore, in accordance with previous studies, we also suggest the revision of the experimental data. Because previous theoretical studies used less accurate methods than we applied here, we recommend our results, -606.5 ( 1.2 and -603.4 ( 1.2 kJ/mol, as new references, respectively, for ∆fH°298(CF2O) and ∆fH°(CF 0 2O). For S°298(CF2O) the NIST-JANAF database lists 258.9 ( 0.1 J/(K · mol). The vibrational frequencies used to calculate the entropy are from the work of Hopper and associates.72 The JPL database lists 259.0 J/(K · mol) and refers to Gurvich’s book.64 Our calculated entropy value, 258.6 ( 1.5 J/(K · mol) agrees well with those calculated from experimental measurements. Nevertheless, due to its smallest uncertainty, the NIST-JANAF value, 258.9 ( 0.1 J/(K · mol) is accepted for S°298(CF2O). FCO. Available experimental heats of formation for the FCO(X2A′) radical show several inconsistencies as detailed below. Most values are only estimates and/or lower or upper and ∆fH°298(FCO). In addition, in almost limits to ∆fH°(FCO) 0 all cases these experimental values have relatively high error bars, which can cause difficulties in the accurate prediction of thermochemical data for related compounds and/or reactions where the heat of formation of FCO is required.73 The most commonly used technique to calculate the heat of formation of the FCO radical is to use the dissociation enthalpy of the F-CO bond via the relation74

∆fH°298(FCO) ) ∆fH°298(F) + ∆fH°298(CO) D°298(F-CO) (2) ∆fH°298(F) and ∆fH°298(CO) are usually taken from accurate experiments; however, the accurate determination of the dissociation enthalpy, D°298(F-CO), is not straightforward. The resulting values from kinetic studies or ion transfer reaction experiments are only rough estimates of the upper and lower and D°298(F-CO). limits of D°(F-CO) 0 The NIST-JANAF database5 suggests -172.1 ( 63.0 and -171.5 ( 63.0 kJ/mol for ∆fH°(FCO) and ∆fH°298(FCO), 0 respectively. These recommendations are based on the standard enthalpy of the reaction F2CO(g) ) CO(g) + 2F(g) and the assumption that D°(Cl-CO)/D °(Cl-COCl) ) D°(F-CO)/ 0 0 0 ) 4. Because the above reaction is the sum of D°(F-COF) 0 + D°(F-COF), simple thermotwo bond energies, D°(F-CO) 0 0 chemical manipulations involving eq 2 yield ∆fH°298(FCO). Burcat’s database7 using Gurvich’s data64 lists -179.4 ( 40.0 and ∆fH°298(FCO), and -180.0 ( 40.0 kJ/mol for ∆fH°(FCO) 0 respectively. These values are based on the energy of the dissociative electron capture reaction CF2O + e ) FCO + Fby Macneil and Thynne.75 Henrici and associates studied the kinetics of the reaction of F2O with CO and the thermal decomposition of F2CO in a shock

Thermochemistry of Several Formaldehyde Derivatives wave tube,73 and both D°(F-CO) and ∆fH°298(FCO) were 0 estimated. On the basis of the reactions F2 + CO f FCO + F e -133.9 and F + CO f FCO, an upper limit, ∆fH°(FCO) 0 kJ/mol, was obtained. The best fit to their overall reaction ) -141.4 kJ/mol.73 Finally, scheme corresponded to ∆fH°(FCO) 0 using previous results and qualitative reasonings, -142.3 ( 21.0 kJ/mol was derived for ∆fH°298(FCO). In their ion transfer reaction investigation, Bowers and Chau74 established new lower and upper limits for ∆fH°298(FCO), -255.2 and -154.8 kJ/mol, respectively. On the basis of a detailed analysis of available experimental data, ∆fH°298(FCO) was estimated to be -175.7 ( 16.7 kJ/mol. It is also noted in ref 74 that the results of Henrici et al.73 may be in error by approximately 20-40 kJ/mol on the grounds that the reaction mechanism used to interpret Henrici’s shock tube data may be more complex than originally assumed and should be reevaluated.74 In a shock tube experiment Gangloff et al.76 determined the dissociation energy of the F-CO and F-COF bonds, and after a detailed review of available findings they suggested ) -276.1 kJ/mol. ∆fH°(FCO) 0 In the photoionization mass spectrometry study of Buckley et al.,62 the F-COF dissociation energy was measured and ) -152.7 ( 12 kJ/mol and ∆fH°298(FCO) ) -152.1 ∆fH°(FCO) 0 ( 12 kJ/mol were calculated from the reaction CF2O f FCO + F. The unimolecular decomposition kinetics of FCO was studied by Knyazev and co-workers.77 From the measured rate constants the standard enthalpy of the reaction FCO f F + CO was derived and was combined with the appropriate NIST-JANAF78 heats of formation values for ∆fH°298(CO) and ∆fH°298(F) to yield -161.2 ( 8.1 kJ/mol for ∆fH°298(FCO). In their early note, Francisco and Zhao79 performed ab initio calculations to resolve the discrepancies between the experimental heats of formation of HCO and FCO radicals. MP4(SDTQ) frozen-core calculations with different triple-ζ basis sets were carried out. Harmonic vibrational frequencies as well as zeropoint energies were also calculated at the MP2 level of theory. From the isodesmic reaction scheme FCO + CH3Cl f ClCO ) -179.9 ( 3.8 kJ/mol was obtained, + CH3F, ∆fH°(FCO) 0 while the isogyric reaction scheme Cl + FCO f ClCO + F ) -179.1 ( 2.9 kJ/mol, in reasonable resulted in ∆fH°(FCO) 0 agreement with the isodesmic data. The average value derived from the two schemes, -179.5 ( 3.3 kJ/mol, was suggested as 79 a new reference for ∆fH°(FCO). 0 The G3 and related methods used by Haworth and coworkers67 provided similar values. The G3, G3[MP2(full)], and G3[MP4(SDQ)] calculations67 resulted in -178.7, -179.9, and -177.4 kJ/mol, respectively, for ∆fH°298(FCO). Zachariah and co-workers80 performed BAC-MP4 calculations on a large number of C1 and C2 hydrofluorocarbons, and for ∆fH°298(FCO) they obtained -182.9 ( 7.4 kJ/mol. Dixon and Feller65 using a composite approach (for the details of their approach please see the section “CF2O” or ref 65) determined -184.5 ( 2.1 kJ/mol for ∆fH°(FCO). 0 The G3MP2B3 study of Janoschek and Rossi81 resulted in ) -180.6 kJ/mol as well as ∆fH°298(FCO) ) -179.9 ∆fH°(FCO) 0 kJ/mol. The more accurate CCSD(T)-CBS (W1U)19 calculations of Janoschek and Fabian82 yielded ∆fH°298(FCO) ) -177.8 kJ/ mol. Breidung and Thiel83 studied the thermochemistry of the fluoroformyloxyl, formyl, and fluoroformyl radicals. Their study is primarily based on the robustness of the CCSD(T) method; however, scalar relativistic effects were also investigated.

J. Phys. Chem. A, Vol. 114, No. 50, 2010 13217 Nevertheless, the valence-valence correlation was separated from the core-valence and core-core contributions, and no electron correlation beyond CCSD(T) was considered. On the basis of 5 reactions and 3 different computational levels, 15 ) -176.1 ( values in total were averaged, and ∆fH°(FCO) 0 2.1 kJ/mol and ∆fH°298(FCO) ) -175.7 ( 2.1 kJ/mol were recommended.83 Since the work of Knyazev et al.,77 no experimental result has been published for the heat of formation of FCO. However, the significant differences between the experimental values together with the remarkably wide bounds to the thermochemical quantities may require the revision of the experimental data. On the other hand, our results are consistent with those obtained in previous theoretical investigations, and due to the higher accuracy of our method, we recommend our data, ∆fH°(FCO) 0 ) -177.2 ( 0.9 kJ/mol and ∆fH°298(FCO) ) -176.7 ( 0.9 kJ/ mol, as new reference values. For S°298(FCO) the NIST-JANAF database5 recommends 248.5 J/(K · mol) calculated from the vibrational frequencies of the spectroscopic study of Milligan et al.84 However, the rotational contribution, which accounts for more than one-third of the total entropy, was estimated only. On the basis of the above estimated geometry but using a different frequency for the bending mode,85 Burcat’s database7 lists S°298(FCO) ) 249.0 J/(mol · K). The G3MP2B3 calculation of Janoschek and Rossi81 resulted in S°298(FCO) ) 249.0 J/(mol · K). Our result, 248.8 J/(K · mol), agrees, within our error bar ((1.5), with the above values. Because our method is more accurate than G3MP2B3 and the experimental values rely on estimated spectroscopic data, we suggest our standard molar entropy, S°298(FCO) ) 248.8 ( 1.5 J/(K · mol), as a new reference. HFCO. No experimental investigation has been published in the literature dealing directly with the enthalpy of formation of formyl fluoride. In the NIST-JANAF database5 the heat of formation values are estimated, without error bars, to be -373.0 and and -376.6 kJ/mol, respectively, for ∆fH°(HFCO) 0 ∆fH°298(HFCO). These heat of formation data are based on the enthalpy of the reaction HFCO ) CO + F + H, which was estimated to be the average of the enthalpies of the reactions CH2O ) CO + 2H and CF2O ) CO + 2F. The auxiliary heat of formation data for CH2O, H, F, CO, and CF2O were set to the appropriate NIST-JANAF values. Essentially, the obtained is the average of ∆fH°(H ∆fH°(HFCO) 0 0 2CO) and ∆fH°(F 0 2CO). Consequently, the uncertainty in ∆fH°(HFCO) is expected to be large.86 Similarly, assuming the equality of the average bond energies of HFCO, CH2O, and F2CO, Gurvich and associates64 estimated as -371 ( 10 kJ/mol. ∆fH°(HFCO) 0 A number of computational studies, using a wide range of methods, have been performed to investigate the thermochemical properties of HFCO. Zhao and Francisco86 using MP2 and MP4 calculations determined -392.5 ( 6.3 kJ/mol for ∆fH°(HFCO). 0 The two isodesmic reaction schemes HFCO + CH4 f H2CO + CH3F and HFCO + HCO f H2CO + FCO were utilized to and the average value was recomcalculate ∆fH°(HFCO), 0 mended. Schneider and Wallington60 recommended -383.3 ( 7.1 kJ/mol for ∆fH°298(HFCO). This value is based on their modified G2(MP2) study on the isodesmic reaction 2HFCO f CH2O + CF2O. This value was also adopted by the JPL database.6 The BAC-MP4 study of Zachariah et al.80 resulted in ∆fH°298(HFCO) ) -382.3 ( 4.4 kJ/mol. Glukhovtsev and Bach87 studied the thermochemistry of vinyl and formyl halides via the G214 composite method, and on the basis of the atomization energy approach, they obtained -390.0 and -393.7

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kJ/mol for ∆fH°(HFCO) and ∆fH°298(HFCO), respectively. 0 Haworth et al.67 obtained -384.9, -384.9, and -383.7 kJ/mol for ∆fH°298(HFCO), respectively, applying the G3, G3[MP2(full)], and G3[MP4(SDQ)] composite methods. Kondo and associates68 performed BAC-MP2 and BAC-MP4 calculations with the 6-31G(d,p) basis set and obtained -389.2 and -392.8 kJ/mol, respectively, for ∆fH°298(HFCO). The AAC-G2/6-31G(d,p) and AAC-G2MP2/6-31G(d,p) calculations resulted in ∆fH°298(HFCO) ) -385.2 kJ/mol and ∆fH°298(HFCO) ) -385.5 kJ/mol, respectively.68 Matus and co-workers69 using CCSD(T)/aug-ccpVTZ geometries performed CCSD(T) single-point calculations with different correlation-consistent basis sets. CCSD(T)/CBS limits were determined using different extrapolation formulas: (i) extrapolating from the aug-cc-pV(D,T,Q)Z basis set results and using an exponential formula, (ii) extrapolating from the aug-cc-pV(Q,5)Z basis set results and using an inverse thirdpower formula. Then the average of the extrapolations was used to estimate the true CCSD(T)/CBS limit. In addition, MP2/augcc-pVTZzero-pointenergies,CCSD(T)/cc-pwCVTZcore-valence correlation energies, and CISD/cc-pVTZ scalar relativistic effects were also taken into consideration. On the basis of the atomization energy approach, ∆fH°298(HFCO) ) -381.2 kJ/mol was obtained.69 Our calculations yielded ∆fH°(HFCO) ) -378.8 ( 1.2 kJ/ 0 mol and ∆fH°298(HFCO) ) -382.5 ( 1.2 kJ/mol. Due to the lack of experimental investigations and the highest accuracy of our method, we recommend our values as new references. On the basis of the spectroscopic studies of Stratton and Nielsen88 and Morgan and his associates,89 the NIST-JANAF database5 recommends S°298 ) 246.5 ( 0.8 J/(K · mol). The JPL database6 refers to Gurvich’s book64 and lists S°298 ) 246.8 J/(K · mol) without uncertainty. Our result, S°298 ) 246.5 ( 1.5 J/(K · mol), agrees well with the JANAF data. Nevertheless, because our value has a wider error bar, we recommend the value S°298 ) 246.5 ( 0.8 J/(K · mol) listed in the NIST-JANAF compilation as the reference. HClCO. Studies, either experimental or theoretical, dealing with the heat of formation of formyl chloride are rather scarce. ) -161.0 Gurvich and associates64 recommend ∆fH°(HClCO) 0 ( 20.0 kJ/mol, which was estimated assuming the equality of the average bond energies in molecules HClCO, H2CO, and Cl2CO. The JPL database6 suggests this value as well. Zhao at the MP4/6and Francisco86 calculated ∆fH°(HClCO) 0 311++G(2df,2p)//MP2/6-311G(2d,2p) level of theory and obtained a significantly lower value, -190.4 ( 6.3 kJ/mol, for The G2 results of Glukhovtsev and Bach,87 ∆fH°(HClCO). 0 ∆fH°(HClCO) ) -189.5 kJ/mol and ∆fH°298(HClCO) ) -192.7 0 kJ/mol, support the above value; however, the calculations of Nguyen and Nguyen90 at the CCSD(T)/6-311++G(3df,2p)// ) MP2/6-31G(d,p) level of theory resulted in ∆fH°(HClCO) 0 -180.6 ( 8.0 kJ/mol and ∆fH°298(HClCO) ) -183.9 ( 8.0 kJ/ mol. ) -180.8 ( 1.7 kJ/mol and Our results, ∆fH°(HClCO) 0 ∆fH°298(HClCO) ) -184.2 ( 1.7 kJ/mol, are in reasonable agreement with those of Nguyen and Nguyen. Because of the highest accuracy of the method applied here as well as the absence of direct experimental results, we recommend our values as new references. For the standard molar entropy of HClCO the JPL compilation6 adopts Gurvich’s64 value of 259.1 ( 0.2 J/(K · mol). In the calculations Gurvich used the results of the spectroscopic study of Hisatsune and Heicklen91 and the microwave investigation conducted by Takeo and Matsumura.92 Our value, 258.7 ( 1.5 J/(K · mol), agrees well with Gurvich’s calcula-

Nagy et al. tions. Nevertheless, due to Gurvich’s tighter error bar on S°298(HClCO), we recommend Gurvich’s value, S°298(HClCO) ) 259.1 ( 0.2 J/(K · mol). FClCO. The available data on the thermodynamic functions of carbonyl chloride fluoride are very sparse. In the NIST) -424.3 ( 33.0 kJ/mol and JANAF database5 ∆fH°(FClCO) 0 ∆fH°298(FClCO) ) -426.8 ( 33.0 kJ/mol are suggested. These values were obtained by averaging the corresponding enthalpies of formation of Cl2CO and F2CO. Using similar assumptions, ) -427.0 ( 20.0 Gurvich et al.64 recommended ∆fH°(FClCO) 0 kJ/mol and ∆fH°298(FClCO) ) -429.0 ( 20.0 kJ/mol. The JPL compilation6 accepts these values as well. On the basis of the results of G3B3 calculations, Burcat’s database7 lists a slightly higher value, -412.5 ( 8.0 kJ/mol, for ∆fH°298(FClCO). Our heat of formation value, ∆fH°298(FClCO) ) -410.9 ( 1.7 kJ/mol, agrees well with that of Burcat. Nevertheless, due to the accuracy of our method together with the lack of direct experimental as well as more accurate theoretical investigations, we recommend our values, -408.4 ( 1.7 and -410.9 ( 1.7 and ∆fH°298(FClCO), kJ/mol, as new references for ∆fH°(FClCO) 0 respectively. For S°298(FClCO) the NIST-JANAF database5 recommends 277.0 J/(K · mol) without an associated error bar. This value relies on the spectroscopic study of ref 93 and the calculations of Lovell and co-workers.94 This is also adopted in Burcat’s database.7 The JPL compendium6 using Gurvich’s value64 reports S°298(FClCO) ) 276.7 ( 0.2 J/(K · mol). To calculate the entropy, Gurvich used the rotational constants from the microwave study of Mirri and associates95 and the fundamental frequencies from the spectroscopic investigation of Nielsen and co-workers.93 Because our result, S°298(FClCO) ) 276.4 ( 1.5 J/(K · mol), is very close to Gurvich’s value, and Gurvich’s value has the smallest associated uncertainty, S°298(FClCO) ) 276.7 ( 0.2 J/(K · mol) is accepted. cis/trans-HOCO. Please note that the notation HOCO is used when the literature cited does not consider the cis and trans forms of the radical. Otherwise, the notations c-HOCO and t-HOCO are applied for cis- and trans-HOCO, respectively. The first experimental value for ∆fH°298(HOCO) was obtained by Back and Sehon96 in 1960. They investigated the thermal decomposition of phenylacetic acid, and from the determined bond dissociation energy, D°298(C6H5CH2-COOH) ) 230.1 kJ/ mol, derived -259.4 kJ/mol for ∆fH°298(HOCO) without giving an error bar. Their calculations were based on the thermochemical relation

∆fH°298(HOCO) ) ∆fH°298(C6H5CH2-COOH) + D°298(C6H5CH2-COOH) - ∆fH°298(C6H5CH2) with the auxiliary data ∆fH°298(C6H5CH2-COOH) ) -313.8 kJ/ mol and ∆fH°298(C6H5CH2 ) 175.7 kJ/mol. Bernecker and Long97 published ∆fH°298(HOCO) ) -163.2 kJ/mol (no error bar was given) from the appearance potential (AP) of C2H5+ from propanoic acid. However, in a different mass spectrometric study conducted by Haney and Franklin,98 ∆fH°298(HOCO) ) -242.7 ( 16.7 kJ/mol was obtained from the AP of CH3+ from acetic acid. In their photoionization mass spectrometric study, Ruscic and co-workers99 studied the reaction of F atoms with HCOOH, DCOOH, and HCOOD, and 8.486 ( 0.012 eV was obtained for the adiabatic IP of HOCO. When this result was combined + ) ) 599.1 ( 2.1 kJ/mol data with the auxiliary ∆fH°(HOCO 0 obtained in ref 100, a value of -219.7 ( 2.5 kJ/mol was derived

Thermochemistry of Several Formaldehyde Derivatives for ∆fH°(HOCO). A few years later, Ruscic and Litorja101 0 revised the earlier results of ref 99, and a new upper limit, EI(tHOCO) e 8.195 ( 0.022 eV, was provided for the ionization energy of t-HOCO. Consequently, the lower limits ∆fH°(t0 HOCO) g -191.6 ( 3.0 kJ/mol and ∆fH°298(t-HOCO) g -194.6 ( 3.0 were suggested.101 Schwarz and Dodson102 measured the 0 reduction potential of alcohol radicals in an aqueous T1+/Tlaq redox system, and the values of the free energies of formation for the radicals were determined. On the basis of the assumption that the free energy of solution of the neutral radicals and that of the corresponding alcohol and formic acid are equal, the gasphase values of ∆fG° and ∆fH° were also estimated, and -196.7 ( 8.4 kJ/mol was obtained for ∆fH°298(HOCO).102 A more recent AP measurement by Holmes and associates103 resulted in a slightly different value, -192.5 ( 12.6 kJ/mol, for ∆fH°298(HOCO). Fulle and associates104 on the basis of the thermal rate constant measurements of the reaction HO + CO h HOCO f H + CO2 estimated -205.0 ( 10.0 kJ/mol for Burcat’s database7 using the ATcT values lists ∆fH°(HOCO). 0 ∆fH°298(t-HOCO) ) -181.3 ( 2.3 kJ/mol and ∆fH°298(c-HOCO) ) -176.3 ( 3.9 kJ/mol. The JPL compilation6 refers to the G3 and CBS-QB3 study of the HCO2 potential energy surface performed by Duncan and Miller105 and suggests ∆fH°298(t-HOCO) ) -181.2 ( 8.0 kJ/mol and ∆fH°298(c-HOCO) ) -173.2 ( 8.0 kJ/mol. The calculated values of ∆fH°(HOCO) are more consistent than the experimental results. In their early work, Yu and coworkers106 performed G2(MP2) calculations on a set of free radicals and ions derived from formic and acetic acids. Although the cis and trans isomers of HOCO were also investigated, only one single value, -193.0 kJ/mol, was given for ∆fH°298(HOCO). The G3MP2B3 calculations on t-HOCO performed by Janoschek ) -182.5 kJ/mol and and Rossi107 resulted in ∆fH°(t-HOCO) 0 ∆fH°298(t-HOCO) ) -185.4 kJ/mol. Feller and co-workers108 also investigated the heat of formation of t-HOCO. Their composite approach, which was based on CCSD(T) calculations, ) -183.7 ( 2.1 kJ/mol as well as yielded ∆fH°(t-HOCO) 0 ∆fH°298(t-HOCO) ) -187.9 ( 2.1 kJ/mol. Fabian and ) -182.6 kJ/mol, Janoschek109 calculated ∆fH°(t-HOCO) 0 ) -176.1 ∆fH°298(t-HOCO) ) -185.6 kJ/mol, ∆fH°(c-HOCO) 0 kJ/mol, and ∆fH°298(c-HOCO) ) -179.2 kJ/mol. These values were obtained from the W1U19 investigation of the reaction OH + CO f H + CO2. Our results for the heat of formation of t-HOCO are -181.3 ( 1.2 and -184.5 ( 1.2 kJ/mol at 0 and 298.15 K, respectively. For ∆fH°(c-HOCO) values of -174.6 ( 1.2 and -177.8 ( 1.2 kJ/mol were obtained at 0 and 298.15 K, respectively. Since the previous theoretical data were extracted from lower level calculations, and considerable discrepancies exist between the experimental results, our results are suggested as new references for the heats of formation of trans- and cis-HOCO radicals. The only experimental value for S°298(HOCO), 250.4 J/(K · mol) without an associated error bar,102,110 is based on the vibrational frequencies of HOCO observed by Milligan and Jacox111 and estimated cis and trans geometries.111,112 From HF-SCF/6-31G* harmonic frequencies Yu and associates106 obtained S°298(HOCO) ) 251.6 J/(K · mol). The G3MP2B3 study of Janoschek and Rossi107 with B3LYP/6-31G* geometries and harmonic frequencies yielded S°298(HOCO) ) 252.0 J/(K · mol). The use of the B3LYP/cc-pVTZ level of theory109 resulted in S°298(tHOCO) ) 251.5 J/(K · mol) and S°298(c-HOCO) ) 251.7 J/(K · mol). Our calculations yielded S°298(t-HOCO) ) 251.4 ( 1.5 J/(K · mol) and S°298(c-HOCO) ) 251.7 ( 1.5 J/(K · mol). Because

J. Phys. Chem. A, Vol. 114, No. 50, 2010 13219 the highest level of theory has been applied here and the experimental value is based on estimated geometries, we recommend our molar entropies as new references. NH2CO. The only available value in the literature for ∆fH°298(NH2CO) is that of Shapley and Bacskay,113 and this result was adopted by the JPL compilation as well.6 Shapley and Bacskay studied the isomerization reactions of the formaldiminoxy radical CH2NO by ab initio quantum chemical methods and found that the NH2CO radical was the most stable among the isomers.113 On the basis of the G2 enthalpies of two isogyric reactions and an isodesmic reaction, a value of ∆fH°298(NH2CO) ) -15.1 ( 4.2 kJ/mol was obtained. Because of the higher accuracy of the method used here we recommend our values, ∆fH°(NH 0 2CO) ) -7.2 ( 1.5 kJ/mol and ∆fH°298(NH2CO) ) -13.1 ( 1.5 kJ/mol, as new references for the enthalpy of formation of this species. To the best of our knowledge, neither an experimental nor a computational value is available in the literature for the standard molar entropy of NH2CO, and therefore, we suggest our value, S°298 ) 256.5 ( 1.5 J/(K · mol), as a reference. Concluding Remarks In this study high-accuracy theoretical calculations have been performed for several formaldehyde derivatives. Although these species are relevant for atmospheric and combustion chemistry, accurate thermochemical functions were not available previously; therefore, the revision of the available reference values has been proposed in most of the cases. This study also confirms the usefulness of high-accuracy quantum chemical investigations, especially for highly reactive species which may not be accessible by contemporary experimental techniques. Acknowledgment. Financial support has been provided by the European Research Council (ERC) under the European Community’s Seventh Framework Programme (Grant FP7/20072013), ERC Grant Agreement No. 200639, and the Hungarian Scientific Research Fund (OTKA), Grant No. NF72194. M.K. acknowledges the Bolyai Research Scholarship of the Hungarian Academy of Sciences. Supporting Information Available: Total energies, ∆ECCSDT(Q), obtained with cc-pVDZ and cc-pVTZ basis sets, equilibrium geometries, rotational constants, harmonic frequencies, and anharmonic corrections. This material is available free of charge via the Internet at http://pubs.acs.org. Note Added after ASAP Publication. This article posted ASAP on November 16, 2010. Due to a production error, the following changes were made: minor revisions were made in the 3rd equation of the Methods section; throughout the text the degree symbol was corrected; units were corrected in the Results and Discussion section. The correct version posted on November 23, 2010. References and Notes (1) Edney, E.; Driscoll, D. Int. J. Chem. Kinet. 1992, 24, 1067–1081. (2) Withnall, R.; Sodeau, J. J. Photochem. 1986, 33, 1–11. (3) Zabel, F. Toxicol. EnViron. Chem. 1994, 46, 153–168. (4) Kudla, K.; Schatz, G. C. In The Chemical Dynamics and Kinetics of Small Radicals; Liu, K., Wagner, A., Eds.; World Scientific Publishing Co.: Singapore, 1995; p 438. (5) Chase, M. W. NIST-JANAF Thermochemical Tables, 4th ed. J. Phys. Chem. Ref. Data, Monogr. 1998, No. 9. (6) Sander, S. P.; Friedl, R. R.; Golden, D. M.; Kurylo, M. J.; Moortgat, G. K.; Wine, P. H.; Ravishankara, A. R.; Kolb, C. E.; Molina, M. J.; Finlayson-Pitts, B. J.; Huie, R. E.; Orkin, V. L. Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies, Evaluation

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