D. J.
888
Bogan, D. W. Setser, and J. P. Sung
HF Infrared Chemiluminescence. Vibrational and Rotational Energy Disposal for Reactions of Fluorine Atoms with Formaldehyde, Acetaldehyde, Benzaldehyde, and Dimethyl Ether D. J. Bogan, t D. W. Setser," and J. P. Sung Department of Chemistry, Kansas State University, Manhattan, Kansas 66506 (Received November 11, 1976)
Infrared chemiluminescence from HF under conditions of arrested relaxation has been used to measure steady-statevibrational and rotational population distributions from the reaction of fluorine atoms with H2C0, CD3CH0,C6H5CH0,CH30CH3,and H202. For F + HzCO the fraction of energy released as HFt vibrational, ( f ~ and ) , rotational, ( f ~ energy ), was 10.43 and -0.12, respectively. The highest H F t , ~level corresponded to the maximum permitted by the thermochemistry, even though HCO is a stabilized radical. In contrast, the highest HFt,J levels from F + CHBCHO (CD3CHO)and CGH&HO were less than the thermochemical limits, which suggests that these radicals relax to the most stable geometry on a slower time scale than the HCO radical, thus making the stabilization energy unavailable to HFt. Abstraction of H from the aldehyde position appears to favor a higher ( f R ) than most other C-H bonds. In seeking an explanation for this, the reactions with (CHJ20, which also favors high ( f R ) , and Hz02,which has similar thermochemistry to H2C0, has been reinvestigated. The CH30CH3reaction also yields a stabilized radical and the stabilization energy was not freely available to HFt. The CH30CH3reaction could be studied under highly arrested conditions and estimation of the initial rotational distributions are presented. The energy disposal characteristics of these reactions are interpreted and discussed with the aid of surprisal analyses. A difference between the rotational energy disposal for the F + HX and F + HR (R = polyatomic) reactions is tentatively identified.
Introduction An ob'ective of our HF infrared chemiluminescence studies'- har, been to ascertain the role of the polyatomic fragment in the energy disposal arising from abstraction of H from polyatomic hydrides by F atoms. Hydride reagents with large radical stabilization energies (defined as the energy difference between the equilibrium geometry of the radical and the geometry of the fragment within the RH molecule) were selected for study. Results have been reported' for the reactions of fluorine atoms with methylbenzene, phenol, acetonitrile, and several alkane^;^ the latter serve as reference molecules.' For the first three reactions, (fv(HF)) was reduced, relative to the reference reactions, and the highest HFt,J energy level was less than that allowed by the thermochemistry. This was taken as evidence that the component of the exoergicity associated with the radical stabilization energy was not released to HFt. In the present work we have measured the energy disposal in the exoergic reactions of aldehydes:
a
F + RHCO + HF? t RCO ( R = H, CH,, CD,, C,H,) A H -49 kcal mol-'
(1)
In order to separate the abstraction pathways from the CH3 and CHO positions in acetaldehyde, CDBCHO was studied. An interesting aspect of this series is the possibility that the time required for release of the stabilization energy may change as the R group increases in mass and size from H to CH3to C6H5. The bond energies of the aldehyde series are surprisingly ~ o n s t a n tand , ~ are considerably lower than those of the isoelectronic ethylenes. The constancy of the aldehyde bond energies has been interpreted6 as evidence for stabilization of the RCO radicals via polarization of the odd electron toward the oxygen, which would be insensitive to the nature of R. In general, the present results support the expectation derived Present address: Chemical Dynamics Branch, Code 6180, Naval Research Laboratory, Washington, D.C. 20375. The Journal of Physicai Chemistry, Vol. 81, No. 9 , 1977
from the methylbenzene series and the radical stabilization energy is not fully available to HFt. The effect for H2C0 is much less significant than for the larger molecules. An interesting finding for the RHCO reactions is that HFt is formed in more extended rotational distributions than for abstraction from most other hydrocarbons; this effect is especially pronounced for H2C0. The formation of higher J levels facilitates the estimation of initial rotational distributions since the rate of relaxation is slow for the higher J levels. Unfortunately the data also suggest that facile vibrational relaxation may occur in collisions between HFt and H&O; therefore, the HFt vibrational relaxation may not be fully arrested for F H2C0. Since reaction with (CH$,O also partitions a higher fraction of energy to rotation, this reaction was reinvestigated so that direct comparison could be made to the RHCO series. Based upon current thermochemistry: the CH20CH3 radical has a significant stabilization energy which also makes the F + (CH3)20reaction of interest. Comparison also was made with the H202reaction, since it has similar thermochemistry to the F + RHCO series and since the radical contains oxygen. The low value of Do(H-O2H) is well known; however, the explanation for the reduced bond energy is not available.8 Information theoretic analysis has shown that the vibrational energy disposal to HF for the methane, silane, germane, and halogen substituted methane reactions closely resembles that of the three-body, F + hydrogen halide, reactions.' The same analysis showed that, as RH becomes larger, moderate deviations from three-body behavior were evident; these can take two general forms: (a) a radical stabilization effect, as exemplified by toluene, and (b) a bulky radical effect (which is attributed to complex encounters between HFt and R) as exemplified by the neopentane reaction. Vibrational surprisal analyses' are applied to the data reported here and the results are compared to our previous work. Linear vibrational surprisal plots are again found, which permits the relative yield of HFt (u = 0) to be estimated. Since good estimates
+
889
HF Infrared Chemiluminescence
of initial rotational distributions were obtained, the rotational distributions also were examined by information theoretic analysis.
Experimental Section The experiments were done under low pressure, steady-state flow conditions using the arrested relaxation apparatus and techniques described previously.' The fluorine atoms are produced by a microwave discharge in SFG. The HFt vibrational and rotational relative populations are obtained from analysis of the HFt infrared chemiluminescence intensity. In this apparatus vibrational relaxation generally is fully arrested and rotational relaxation is partially arrested. Based upon computer simulation of the rotational relaxation (see Results section) the initially formed HFt product molecules undergo 10-20 collisions before passing out of the observation region. Even this number of collisions can result in vibrational relaxation; in such instances the u level may be reduced without an appreciable change in J level." The degree of relaxation may vary in different systems and caution always must be exercised. For the HzCO experiments a heated reagent inlet line was necessary; the HzCO was produced by thermal decomposition of the trimer (paraldehyde). Acetaldehyde-d3 was made by proton exchange of CH3CH0 in ca. 1 N D2S04in D20which was sealed in a pyrex vial and allowed to exchange for 12 h at 70 "C. This procedure yielded an equilibrium mixture of CD3CH0, CDZHCHO, CDHZCHO, and CH3CH0 via protonation and exchange of the enol form of acetaldehyde: 0
HOD+ I
It
D,O+t CH,C-H
+ HD,O+
++
CH,=CH
HOH' I
t.-f
CHD=CH-
0 II
CH,D--C-H (2)
Gas chromatographic analysis of the products of the exchange reaction showed that some dimer (aldol) was present. Separation of chemically pure acetaldehyde was accomplished by fractional distillation of the acidic product mixture under dry nitrogen at 1atm; the fraction collected at 20-35 "C was retained. The distillations were done very slowly in order to avoid polymerization of the entire sample. Four exchanges yielded acetaldehyde which was 96% deuterated in the methyl position and 7% deuterated in the aldehyde position (analysis was by mass spectrometry and NMR). The acetaldehyde was metered to the reaction zone from a reservoir containing the liquid sample. Dimethyl ether was used directly from a Matheson lecture bottle. Benzaldehyde (J.T. Baker Chemicals) and 98% H202(FMC Corporation, Buffalo, N.Y.) were flowed directly into the reaction vessel from liquid reservoirs. Due to their low vapor pressures, both the reservoir and the inlet line were heated to -35 "C. For H20zthe pyrex reservoir and inlet line were cleaned with 2% aqueous HF followed by several rinses with distilled water; fluorocarbon stopcock grease was used for the stopcocks and standard taper joints. The low temperature reaction vessel, the discharge source for the F atoms, the mixing nozzles, and internal mirror arrangement were identical with those previously used.' The emission spectra in both the fundamental and first overtone regions were recorded with the Perkin-Elmer Model 210 B single beam monochromator and liquid nitrogen cooled PbS detector. The signal was chopped and amplified with a PAR phase-lock amplifier. For the reactions of F with H2C0, CH3CH0, and CH3OCH3, the flows of both SF6 and substrate were 1-2
X lo4 mol s-'. For the reactions of H202and C6H6CH0 the hi hest flows of substrate obtainable were 1
0.29 (0.12) 0.29 (0.16)
0.12 0.64
2
sum over u 2 1 u=l
(fR)
0.72 0.75 0.78'
0.20 (0.05) 0.18 (0.05) 0.13 (0.09)
0.24 (0.08) 0.29 (0.10) 0.20f
0.22 0.22 0.21
0.25 0.33 0.29
(0.11)
0.13 0.67 1.02 0.92
0.14
The numbers in parentheses are the gRmp values from the model I11 prior distributions. The values from models I and The numbers in parentheses are the (gR) values from the model I11 prior distributions. The ( g ~values ) from the model I and I1 distributions are roughly constant for all v levels and are approxiThe low value for f ~ ~ = / ( lf u ) for u = 3 of HC1 arise from an energy constraint; the mately 0.40 and 0.25, respectively. next higher Jvalue would exceed the energy limit; f R m P / ( l - f u ) would be 0.37 if the next higher Jlevel was taken as the maximum, which is within the experimental uncertainity. The data for the F t HCl reaction were taken from ref 23. ~ f ~ m~ and ~ ,( ~f ~for ), e The initial rotational distribution for u = 1 may be unreliable, see text. f The low value for f u = 3 of CH,OCH, is not formally constrainted by the available energy. However, interpretations given in the text suggest that dynamical constraints d o limit the energy to - 4 0 kcal mol-'. See the entry E = 40 kcal mol-'.
I1 are 0.5 and 0.2, respectively, for all v levels.
c 1
'
' mm'
'
I
l
l
1
0:
m
OII
em -3 0
a
0
-20 i;
-
?+
2 -10
VI 7
D
-00;
a, --I0
00
I
I
02
I
I
04
I
00
fRl(1.o-f")
08
10
Flgure 8. Rotational surprisai plot for v = 2 from F 4- H&O reaction. The scale for the experimental (W), and prior distribution (solid lines) is on the left-hand ordinate and that for I(f,) is on the riiht-hand ordinate. The surprisai points are shown as 0, 8, and 0 for models I,11, and 111, respectively.
or gRis worthwhile and a summary is given in Table V (fR"P is the f R for the most probable rotational level). It is evident that the average rotational energy released to HFt is significantly less for the polyatomic systems than for the HC1 reaction. The three models used for the prior distributions gave an invariance of & with vibrational level, i.e., the POUR) plots for various u levels all resemble those of Figure 8. For the vibrating rotor approximation, it can be showngathat for models I and I1 the & values are 0.50 and 0.20; these values also closely agree with the exact numerical results of eq 11. The iR value from model I11
I
0.0
0.2
0.4
1- f"
I
0.6
1
0.8
J 1.0
Flgure 9. A plot for the most probable fraction of rotational energy for each vibrational level vs. 1 - 6.Two sets of points corresponding to available energies of 45 (A) and 40 (V)kcal mol-' are given for F C CH30CH3;the latter corresponds to a reduction in available energy by an amount that is equivalent to the stabilization energy of CH20CH3. Two points, corresponding to J = 11 and 12, are shown for v = 1 from F CH20, the experimental uncertainty is even larger than implied by these two points.
+
will, of course, depend upon the total number of vibrational modes in the R fragment; see Table V. The experimental &?R values can be compared on a plot of fRmp vs. (1- f,) and " ~ F + HC1 the results are shown in Figure 9. The f ~ from is a linear function of 1 - fu and the average value of & is 0.5, which is the prior result for model I. Virtually the same rotational energy disposal results have been found The Journal of Physical Chemistry, Vol. 81, No. 9, 1977
D. J. Bogan, D. W. Setser, and J.
896
+
for the C1 HI reaction,gd which has very similar dynamical proper tie^.^'"' The plots of fRmP vs. 1 - f , for CH30CH3and CHzO are approximately linear, except for the u = 1 point of CHzO. If a reduced energy (the thermochemical energy minus the radical stabilization energy) is used for CH30CH3,the linearity is improved and " ~ slope is increased somewhat. The slopes from the f ~ vs. 1- f, plots for CHzO (-0.25) and CH30CH3(-0.20) are close to the prior value from model I1 (0.20). Apparently model ZZ is the better prior model for rotational energy disposal for the F + HR polyatomic hydride reactions; whereas, model I is better for the three-body F atom reactions.
Discussion A. Vibrational Energy Disposal. The vibrational energy disposal for reactions of fluorine atoms with simply substituted methanes is very similar to true three-body, F + HX, cases.' However, surprisal plots for model I were nonlinear for R groups that were bulky (such as tert-butyl) or if R had a large radical stabilization energy. In these cases linearity could be restored by lowering the available energy. For the F + toluene reaction giving the resonance stabilized benzyl radical, a linear surprisal plot (with a Xv value that was in excellent agreement with results from substituted methanes) was obtained if the available energy was set at the value given by the highest observed HFt level. This energy coincides with the thermochemical energy less the benzyl resonance energy. The reaction of F + neopentane, which exemplifies the bulky substituent cases, did not fit a linear model I surprisal plot unless the energy was reduced to less than the energy of the highest observed HF' level. Such an energy reduction, which gave a more negative hv than that for substituted methanes, is not physically realistic. This type of nonlinear surprisal, with model I prior, was attributed to secondary encounters resulting from the bulky neopentyl group blocking the exit trajectory of HFt. This effect seems to exist for several large R group.' Both of the effects described above are a consequence of the H being rapidly transferred from the R to F and the subsequent scattering of HFt from the R fragment, which are the dominant dynamical features of these r e a ~ t i o n s . ~ For the sake of the present discussion, the effects from resonance and distortion stabilization energies of the R group are distinguished. The release of distortion energy results from relaxation of the nuclei of the initially formed radical to its equilibrium (lowest energy) geometry. The release of resonance energy involves relaxation to the equilibrium configuration in concert with delocalization of the odd electron created by the H abstraction process. The distortion stabilization energy frequently is associated mainly with a localized change in geometry, such as a reduction or extension in one bond length; whereas, the resonance stabilization energy is associated with changes of many coordinates. The constancy of Doo(H-COR) was attributed to the stabilization energy arising from a POlarization of the odd electron of the free radicals toward oxygen, which makes the nature of the R group unimp ~ r t a n tand , ~ the RCO stabilization energy is a distortion rather than a resonance energy effect. The reduced Do(H-CHO) relative to Do(H-CzH3) must be a consequence of an intrinsically reduced binding energy and should not be associated entirely with a radical stabilization effect. The r(C-H), r(C-0), and H-C-0 angle in HCO and HzCO are 1.110 vs. 1.102 A, 1.171 vs. 1.210 A, and 127.4 vs. 121.l0, r e s p e c t i ~ e l y . ~The ~ ~ ~shortened ~ CO and lengthened H-C distances are reflected in a very weak The Journal of Physical Chemistry. Vol. 81, No. 9. 1977
P. Sung
bond, Doo(H-CO) = 33 kcal mol-'; the corresponding bond in acetyl is also very weak: Doo(CH3-CO)= 13 kcal mol-'. On this basis, the geometry changes in CH3C0 upon abstraction of H from CH3CH0 should resemble that of the formyl fragment. The critical factor allowing coupling of radical stabilization energy to the departing HF may be the time scale for the changes in geometry. A sufficiently rapid change should allow the HFt to acquire energy up to the thermochemical limit for, at least, a few encounters even though the probability for such collisions may not be high. The slowest motion in formyl is the bending mode which has a period of -3 X s. The period for the CD3C0 bending mode would be about a factor of 3 longer. Thus, we suggest that HCO has a stabilization energy e q d to that of CH3C0 and C6H6C0, but that the more rapid relaxation rate of the initially formed HCO allows the HFt to sample the full exoergicity of the F H2C0 reaction. This interpretation is based upon the overall difference in the vibrational energy disposal and the highest observed HF,j level between HzCO and CDBCHO(or C6H5CHO). It is unlikely that relaxation was sufficiently extensive to affect this general interpretation. This interpretation of the difference in the vibrational energy disposal presupposes that direct H abstraction is the sole product channel leading to HFt. A chemically reasonable alternative channel is F addition followed by three-centered unimolecular elimination
+
F + H,CO
-+
H,FC-O*
-+
HF
+ HCO
(13)
The lifetime of the chemically activated radical would be short and the HFt product vibrational distribution could extend to high u levels; however, the distribution should favor lower u levels than the direct H abstraction reaction.% For CH3CH0 and C6H6CH0there are many more internal modes and the chemically activated radical should be longer lived; hence, the energy disposal to HF for the elimination channel should give much less energy to HFt. Surprisal analysis would reveal this in the form of a smaller -Av value, if elimination was the sole channel, and a nonlinear surprisal plot if direct abstraction occurs in competition with elimination. As evidence against elimination we note: (a) the HzCO surprisal plot is linear and (b) the HF elimination in eq 13 must compete with displacement of H or CH3, which seems unlikely for CD3CHFO*; yet the HF' vibration and rotational distributions are similar to those from HzCO. In conclusion, addition followed by elimination is unlikely, but cannot be completely ruled out. The 02H stabilization energy must be significant since Doo(02-H)16is only 46 kcal mol-'. The structure of H o p can be compared to H202:28r(0H) = 0.977 vs. 0.950 A, r(0-0) = 1.335 vs. 1.475 A, and the HOO angle = 104.1 vs. 94.8'. The relaxation of OzH involves both bonds and the HOO angle. The bending modes of HOz and HCO have nearly the same frequency and the time scale for relaxation of HOz also should be -3 X s. The effect of the distortion (stabilization) energy seems to be to reduce the (fv) and the -Xv (model I) value, relative to HBr or the substituted methanes, but the influence is not so great as to introduce nonlinearity into the surprisal plot or to give a large energy defect. The relaxation of the CHz0CH3radical presumably will be on the same time scale as CH3C0. Thus, the stabilization energy might be expected to influence the linearity of the model I surprisal plot and the highest observed HFtvJ level, as experimentally observed. This interpretation rests on the validity of the Doo(H-CH20CH3)of ref
HF Infrared Chemiluminescence
897
7. If this bond energy were raised to the value of a normal primary C-H bond energy, the information theoretic parameters would be very similar to other substituted methanes. The (fR), however, would be somewhat larger than for most other hydrocarbons (see next section). Attempts were made to measure the rate constants, relative to CH4, for F + CH3CHO and H202.29 For CH3CH0 the rate constant was 1.6 times greater than for CH4and the rate of abstraction from the aldehyde position is thought to differ little from the methyl hydrogen. For Hz02a good measurement could not be obtained, because of the low vapor pressure of H202and because of apparent fast relaxation of HFt. However, the qualitative observations show the rate constant to be 0.1 of that for CHI. B. Rotational Energy Disposal. The contour maps of the detailed rate constants from the CH20 and CH30CH3 reactions may be compared with that of F + HCl.23 For the latter the ridge of highest probability follows a line at fR/(l - f,) = 0.5, i.e., the fraction of the available energy partitioned to rotation or translation is the same for each vibrational level. This type of energy disposal, known as inverse correlation of vibrational and rotational energy, also is found for C1+ HLlsb Since both of these three-body reactions have dynamical features4that are similar to those for F + HR, they will be used as reference reactions for comparisons of rotational energy disposal from polyatomic reactions. In general the CH30CH3and CH20 contour plots do not show as strong an inverse correlation as that for F + HC1. Although the shapes of Figures 4 and 5 show detailed differences, common features seems to be lack of strong inverse correlation and failure to give HFt in the highest possible J states for u = 1 of CH30CH3and u = 1 and 2 of CH20. We believe that the estimated initial rotational distributions for F + H2CO and F + CH3OCH3 are sufficiently reliable to conclude that a fundamental constraint restricts the formation of the HF molecules in the highest J states for the lower vibrational levels. Furthermore, this result appears to be relatively general for polyatomic HR.16 Although uibrationul energy disposal strongly resembles the three-body case for simpler polyatomics, the rotational energy disposal deviates from the three-body behavior with the difference being especially severe for the low vibrational levels. The information analysis, which suggested that the model I1 prior was a useful reference, implied that the R fragment may acquire significant amounts of rotational energy (and angular momentum). This possibility is examined in more detail below. The conservation equation for total angular momentum of reaction 1 is +
+
+
+
+
L + JHR = L ’ + S H F+SR (14) The primed and unprimed quantities refer to reactants and products, respectively; L denotes orbital angular momentum and J rotational angular momentum. The range of possible values for total angular momentum can be estimated from the scalar quantity IL f JI. To evaluate this expression for F + H2C0,the rate constants for H2C0 and C2HG were assumed to be equal. Using the relative rate data of the following paper and the recommended3’ rate constant for F + CH4, kF+ co = 2 X lo-’’ cm3 molecule-1 s-1 and 6F+HzC0 = 25 This cross section coincides with a maximum impact parameter of 2.8 A, assuming a reaction probability of 1.0 for all b less than bma. Using this b,,, the orbital angular momentum in the entrance channel is equal to or less than 37h at 300 K; the average rotational angular momentum of H2C0 (using the rotational constants of HerzbergZ5)is 14h. For
i?.
direct reactions in which the initial and final reduced masses are nearly unchanged and for which repulsiye energy release does not contribute strongly to J’HF, L’ usually is the dominant angular momentum term for the products. This tendency should be reinforced for these reactions by the relatively low value of (J).Within these approximations, the @_tal a;ngular momentum for F + H20 has the range 23h < IL f JI < 51h; this lower limit to J’m is comparable to the limitation imposed by conservation of total energy for u = 1 and exceeds the energy limit for u > 1. Hence, the use of energy conservation only is acceptable in the computation of the prior distributions, eq 7 and 8. The product momentum vectors S’HF, and S’R may combine in various ways so as to give a total magnitude of 23 to 51h. The HCO radical has rotational constants24 of A = 22.4, B = 1.5, C = 1.4 cm-’, and can take up a sizeable amount of the angular momentum. (At 300 K, the thermal average angular momentum of HCO is ( J ) = 12h.) For most polyatomic R the rotational constants are even smaller and the R group can acquire considerable angular momentum even at relatively low energy. This is in distinct contrast to the three-body reaction for which the energy must be released as the HF vibrational, HF rotational or relative translational energy (excluding electronic4 excitation of R). The reactive F + HX collisions involving large amounts of angular momentum presumably favor formation of HFt in high J levels. For polyatomic cases, the R group also can acquire angular momentum and HFt need not be formed in high J states. The loss of population from the high J levels presumably coincides with a gain for the intermediate J levels, without a significant change in vibrational level, because the vibrational energy disposal for simple cases of F HR reactions resembles that of the three-body reactions. Inspection of the three-body trajectory results4 supports this interpretation because rotational energy exchange between HFt and polyatomic R could occur for the trajectories having complex behavior or experiencing secondary encounter^.^ Furthermore, such trajectories probably are more prevalent for polyatomic reagents.
e’,
+
Conclusions The vibrational and rotational energy disposals to HF from the F + CH20 rotations ( ( f v )1 0.43 and ( f R ) N 0.12) and the F + CH30CH3( ( f , ) = 0.45 and (fR) = 0.13) have been measured. The vibrational energy disposal for the F + CD3CH0, C6H6CH0, and H202reactions also was characterized. These reactions all release less vibrational energy to HF than typical hydrocarbon reactions. All of these reactions yield stabilized radical products. For the reactions giving large radicals (CD3C0, C6H&0, and CH20CH3) the stabilization energy was not available to the HF. However, for H2C0 and H202the stabilization energy was, at least, partially available. The reason for this is suggested to be the shorter time required for the smaller radicals to relax to their equilibrium geometry. Information theoretic analyses of the HF vibrational and rotational distributions were done. Vibrational surprisal plob were generally linear, except for the reactions yielding the large stabilized radicals. For these cases it was necessary to reduce the available energy (for a three-body prior) to obtain linear plots. Except for the reactions yielding the large stabilized radicals, the three-body, F HX, reactions provide a useful analogy for the vibrational energy disposal. Based upon the H2C0 and (CH3)20 examples, the rotational energy disposal for polyatomic systems appears to differ from the three-bod case with less rotational energy being released to HFY Indirect
+
The Journal of Physical Chemistry. Vol. 81, No. 9, 1977
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Setser et al.
arguments suggest that the polyatomic group acquires rotational energy and angular momentum. Acknowledgment. One of us (D.J.B.) wishes to acknowledge helpful discussions with Drs. D. S. Y. HSU,J. W. Hudgens, and W. A. Sanders. We are grateful for the support provided by the National Science Foundation
(MPS75-02793). References and Notes (1) D. J. Bogan and D. W. Setser, J . Chem. Phys., 64, 586 (1976). (2) K. C. Kim, D. W. Setser, andC. M. Bogan, J. Chem. Phys., 60, 1837 (1974). (3) (a) K. C. Kim and 0. W. Setser, J. Phys. Chem., 77, 2493 (1973); (b) J. H. Parker, Int. J. Chem. Klnet., 7 , 433 (1975). (4) R. L. Johnson, K. C. Kim, and D. W. Setser, J. Phys. Chem., 77, 2499 (1973). (5) (a) R. K. Soily and S. W. Benson, J. Am. Chem. Soc., 93, 1592 (1971); (b) D. M. Goiden and S. W. Benson, Chem. Rev., 69, 125 (1969). (6) W. H. Duewer and D. W. Setser, J. Chem. Phys., 58, 2310 (1973). (7) F. R. Cruickshank and S. W. Benson, Int. J . Chem. Klnet., 1, 381 (1969); Deo(H-CH20CH3)is 4-5 kcai mol-‘ less than DedH-CH2CH3) which implies the presence of a radical stabilization energy. (8) S. W. Benson, J. Chem. fduc., 42, 502 (1965). The OH single bond energy varies greatly from one compound to another but good explanations have not been advanced to explain these bond energy changes. (9) (a) R. B. Bernstein and R. D. Levine, Adv. At. Mol. Phys., 11, 216 (1975); (b) R. D. Levine and R. B. Bernstein, Acc. Chem. Res., 7, 393 (1974); (c) R. D. Levine and R. B. Bernstein, “Modern Theoretical Chemlstry”, W. H. Miiier, Ed., Plenum Press, New York, N.Y., 1975; (d) R. D. Levine, B. R. Johnson, and R. B. Bernstein, Chem. Phys. Lett., 19, 1 (1973). (10) M. A. Nazar, J. C. Polanyi, W. J. Shrlac, and I. J. Sioan, Chem. Phys., 16, 411 (1976). (11) D. E. Mann, B. A. Thrush, R. D. Lide, J. J. Ball, and N. Acquista, J. Chem. Phys., 34, 420 (1966). (12) (a) J. M. Herbelin and G. Emanual, J . Chem. Phys., 60, 689 (1974); (b) R. Herman, R. W. Rothery, and R. J. Rubiin, J. Mol. Spectrosc., 2 , 369 (1958). (13) H. E. O’Neai and S. W. Benson, “Thermochemistry of Free Radicals”, in “Free Radicals”, J. K. Kochi, Ed., Wiiey-Interscience, New York,
N.Y., 1973, pp 275-359. (14) W. A. Chupka and J. Berkowitz, J . Chem. fhys., 54,5126 (1971). (15) B. de B. Darwent, Natl. Stand. Ref. Data Ser., Natl. Bur. Stand., No. 31 (1970). (16) K. Tamagake and D. W. Setser, unpublishedresults. Experiments with an improved arrested relaxation reaction vessel and with observation of the emission intensity with a Fourier transform spectrometer have confirmed the F CH30CH3distributions of Flgure 3. (17) (a) J. C. Pohnyi and K. 6. Woodail, J. Chem. Phys., 56, 1563 (1972); (b) A. M. G. Ding and J. C. Polanyi, Chem. Phys., 10, 39 (1975). (18) (a) D. H. Mayiotte, J. C. Polanyi, and K. 6. Woodall, J. Chem. Phys., 57, 1547 (1972); (b) C. A. Parr, J. C. Poianyi, and W. H. Wong, lbkl., 58, 5 (1973). (19) (a) I. Procaccia, Y. Shlmoni, and R. D. Levine, J. Chem. Phys., 83, 3181 (1975); (b) R. D. Levine, R. 6. Bemstein, P. Kahma, I. Procaccla, and E. T. Upchurch, ibld., 64, 796 (1976). (20) Double peaked rotational distributions normally are associated with two different reaction dynamics, see the following references for examples: (a) H. Heydtmannand J. C. Polanyi, App. Opt., 10, 1738 (1971); (b) M. A. Nazar, J. C. Polanyi, and W. T. Skrlac, Chem. Php. Lett., 29, 473 (1974). (21) (a) D. W. Smith and L. Andrews, J . Chem. Phys., 60, 81 (1974); (b) G. E. Ewing, W. E. Thompson, and G. C. Pimentei, /bid., 32, 927 (1960); (c) D. E. Miiiigan and M. E. Jacox, ibid., 51, 227 (1969). (22) T. Shimanouchi, Natl. Stand. Ref. Data Ser., Natl. Bur. Stand.,No. 39 (1972). (23) (a) A. M. G.Ding, L. J. Kirsch, D. S. Perry, J. C. Polanyi, and J. K. Schreiber, Faraday Discuss., Chem. Soc., 55, 252 (1973); (b) K. Tamagake and D. W. Setser, unpublishedresuks. These data agree well with the results from ref 23a. (24) J. A. Austin, D. H. Levy, C. A. Gottiieb, and H. E. Radford, J. Chem. Phys., 60, 207 (1974). (25) G. Herzberg, “Molecular Spectra and Molecular Structure, 111. E W o n Spectra and Electron Structure of Polyatomic Molecules”, Van Nostrand, New York, N.Y., 1966, p 612. (26) H. W. Chang, D. W. Setser, and M. J. Perona, J. Phys. Chem., 75, 2070 (1971). (27) Y. Beers and C. J. Howard, J . Chem. Phys., 84, 1541 (1976). (28) R. L. Redlngton, W. B. Olson, and P. C. Cross, J. Chem. Phys., 36, 1311 (1962). (29) R. Foon and M. Kaufman, Prog. React. Klnet., 8, No. 2, 81 (1975). (30) D. J. Smith, D. W. SeW, K. C. Klm, and D. J. Bcgan, J. Phys. Chem., following paper in this issue. (31) J. P. Sung and D. W. Setser, Chem. Phys. Left., in press.
+
HF Infrared Chemiluminescence. Relative Rate Constants for Hydrogen Abstraction from Hydrocarbons, Substituted Methanes, and Inorganic Hydrides D. J. Smith,“ D. W. Setser,” K. C. Kim,lb and
D. J.
Bogan’’
Department of Chemistry, Kansas State University, Manhattan, Kansas 66506 (Received November 1 I, 1976)
The relative HF infrared emission intensities from the reactions of F atoms with 24 organic and inorganic hydride molecules, RH, have been measured in a flowing-afterglowapparatus at room temperature. By operating under conditions such that the emission intensity is first order in [RH] and the relaxation of the initial HF’ vibrational populations was minimal, rate constants, relative to CH4,for HF formation were obtained. By combining these measurements with absolute rate constants for selected members of the series, the relative rate constants can be converted to absolute room temperature rate constants. Since the initial HFt vibrational populations have been measured for these hydride molecules, the current measurements can provide absolute rate constants for formation of individual HFt vibrational levels. In addition to the relative rate constant measurements from the flowing-afterglow apparatus, chemiluminescence results from cold-wall arrested relaxation experiments are presented for reactions of F + various ethers and methanol-dl. The HFtUJdistributions from $he cyclic ethers and the magnitude of the rate constants for ethers vs. alkanes are discussed with respect to the enhanced rotational energy disposal for the F + CH30CH3reaction.
The Journal of Physlcal Chemistry, Vol. 8 1 , No. 9 , 1977
