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(2) D. E. Irish in “Ionic Interactions”, Vol. 11, S. Petrucci, Ed., Academic Press, New York, N.Y., 1971, Chapter 9. (3) D. E. Irish and M. H. Brooker in “Advances in Infrared and Raman Spectroscopy”, Vol., 2, R. J. H. Clark and R. E. Hester, Eds., Heyden, London, 1976, Chapter 6. (4) s. Petrucci in “Ionic Interactions”, Vol. 11, S. Petrucci, Ed., Academic Press, New York, N.Y., 1971, Chapter 7. (5) A. K. Covington and T. Didkinson, Eds., “Physical Chemistry of Organic Solvent Systems“, Plenum Press, London, 1973, p 5. (6) J. T. Bulmer, D. E. Irish, F. W. Grossman, G. Herriot, M. Tseng, and A. J. Weerhelm, Appl. Specfrosc., 29, 506 (1975). (7) A. R. Davis, D. E. Irish, R. B. Rodin, and A. J. Weerheim, Appl. Specfrosc., 26, 384 (1972). (8) S. Petrucci, J. Phys. Chem., 71, 1174 (1967); G. S. Darbari, M. R. Richelson, and S. Petrucci, J . Chem. Phys., 53, 859 (1970). (9) J. 0.Mikhailov, Dokl. Akad. Nauk. SSSR, 89, 991 (1953). (10) H. Farber and S. Petrucci, J . Phys. Chem., 80, 327 (1976). (11) P. Gans, ”Vibrating Molecules”, Chapman and Hall, London, 1971, p 192. (12) J. L. Burmeister, Coord. Chem. Rev., 1, 205 (1966). (13) D. Paoli, M. Lucon, and M. Chabanel, Specfrochim. Acta, Part A , 34, 1087 (1978). (14) R. S. Tobias and M. Yasuda, Inorg. Chem., 2, 1307 (1963). (15) F. J. C. Rossotti, H. S. Rossotti, and R. J. Whewell, J . Inorg. Nucl. Chem., 33, 2051 (1971). (16) T. G. Chang and D. E. Irish, Can. J . Chem., 51, 118 (1973). (17) T. G. Chang and D. E. Irish, J. Phys. Chem., 77, 52 (1973). (18) T. G. Chang and D. E. Irish, J . Solution Chem., 3, 161 (1974).
Tyrrell (19) G. J. Janz, K. Babsubrahmanyam, and 8. G. Ollver, J. Chem. Phys., 51, 5723 (1969). (20) R. E. Hester and R. A. Plane, J . Chem. Phys., 40, 411 (1964). (21) D. E. Irish and G. E. Walrafen, J. Chem. Phys., 48, 378 (1967). (22) J. D. Riddell, D. J. Lockwood, and D. E. Irish, Can. J . Chem., 50, 2951 (1972). (23) G. R. Lester, T. A. Gover, and P. G. Sears, J. Phys. Chem., 80, 1076 (1956). (24) M. Eigen and L. DeMaeyer in “Rates and Mechanisms of Reactions”, Part 11, 2nd ed.,A. Weissberger, Ed., Interscience, New York, 1963, Chapter XVIII. (25) J. Stuehr and E. Yeager in “Physical Acoustics”, W. P. Mason, Ed., Academic Press, New York, N.Y., 1965, Vol. 11, Part A, p 386. (26) J. Nixon and R. A. Plane, J. Am. Chem. SOC.,84, 4445 (1962). (27) D. E. Irish and R. V. Thorpe, Can. J . Chem., 53, 1414 (1975). (28) R. M. Fuoss and F. Accascina, “Electrolytic Conductance”, Interscience, New York, N.Y., 1959. (29) F. H. Fisher, J. Phys. Chem., 66, 1607 (1962). (30) S. D. Hamann, P. J. Pearce, and W. Strauss, J. Phys. Chem., 68, 375 (1964). (31) K. Tamm in “Dispersion and Absorption of Sound by Molecular Processes”, D. Sette, Ed., Academic Press, New York, N.Y., 1983, p 192. (32) P. Hemmes, J. Phys: Chem., 78, 895 (1972). (33) C. Langford and H. Gray, “Ligand Substitution Dynamics”, W. A. Benjamin, New York, N.Y., 1965, pp 60-61. (34) J. E. Leffler and E. Grunwald, “Rates and Equilibria of Organic Reactions”, Wiley, New York, N.Y., 1963, p 156 ff.
Ab Initio Calculation of the Equilibrium Geometries and One-Electron Properties of Formyl Fluoride and Formyl Chloride James Tyrrell Department of Chemistry and Biochemistry, Southern Illinois University at Carbondale, Carbondale, Illinois 6290 1 (Received March 21, 1979; Revised Manuscript Received June 11, 1979)
Equilibrium geometries for formyl fluoride and formyl chloride have been obtained by ab initio geometry optimization calculationswith a double {or close to a double l basis set. A number of one-electronproperties for the equilibrium geometries have been determined. These include various multipole moments, quadrupole coupling constants, and average diamagnetic shielding. Comparison of the calculated properties with experimental values is made where possible.
Introduction Formyl fluoride (HCOF) has been studied extensively by using a variety of spectroscopic techniques. Aside from interest in observing the effect of substitution of a fluorine for a hydrogen in formaldehyde, formyl fluoride is also the simplest representative of the acyl fluorides. Also photolysis of formyl fluoride (A 2 1550 A) produces HF infrared laser emission. On the other hand formyl chloride (HCOC1) has only recently been prepared by ozonolysis of 1,2-dichloroethane and its existence confirmed by observation of its infrared spectrum.l The microwave spectrum of formyl chloride has been analyzed by Takeo and Matsumura2who determined its geometry, quadrupole coupling constants, and its dipole moment. Frost, McDowell, and Westwood3 have obtained the photoelectron spectrum of formyl chloride and analyzed it with the aid of a CNDO/BW calculation. A band at 11.61 eV (11.51 sh) was assigned to the highest occupied molecular orbital, a nonbonding oxygen orbital with a significant chlorine contribution. Bands at 12.38 and 12.46 eV were assigned to chlorine 3p, and 3p, orbitals respectively while a band at 15.28 eV was assigned to the 7rco orbital. The remaining bands at 16.43 (16.29 sh), 17.2, and 20.3 eV were assigned to u orbitals. 0022-3654/79/2083-3276$0 1.OO/O
There have been numerous determinations of the ground state structure of formyl fluoride with r n i c r o w a ~ e , ~ - ~ electron diffra~tion,~ and infrared’O techniques. These studies give largely consistent results except for the HCO and HCF angles which are determined to be 127.3 and 109.go,5110.2 and 127.9°,4or 123 and 1140a7The geometries determined by Miller and Curl5 and LeBlanc, Laurie, and Gwinn6 which are in good agreement are now taken as the generally accepted values. The numerical values of the dipole moment components of formyl fluoride have been found to be (pal= 0.595 D and lpbl = 1.934 Dq6Rock, Hancock, and Flygarell have obtained values for the quadrupole moments, second moments, and diamagnetic and paramagnetic susceptibilities for formyl fluoride. The deuteron quadrupole coupling constant has been determined by Kukolich12 to be 205 kHz along the D-C bond direction in DCOF. Klimek13obtained the photoelectron spectrum of formyl fluoride assigning bands at 12.37 and 13.97 eV to the nonbonding oxygen orbital and the TCO orbital, respectively. There have been numerous semiempirical and ab initio calculations on formyl fluoride. Czismadia et obtained a total energy of -212.1139 hartrees and dipole moment components px = -1.9410 D and .uy = -2.1546 D using the 0 1979 American Chemical Society
The Journal of Physical Chemistry, Vol. 83, No. 25, 1979 3277
Ab Initio Calculations of HCOF and HCOCI
TABLE I: Coordinates for Formyl Fluoride and Formyl Chloride (Equilibrium Geometries)a Y
X
H C 0 F
H C 0
c1
a
z
Formyl Fluoride - 2.823092 -0,122518 -0.810765 -0.300197 0.427898 - 2.174871 0.301614 2.027155
0.0 0.0 0.0 0.0
Formyl Chloride -2.919940 -1.555108 -0,895593 - 1.438281 0.575153 -3.141980 0.128411 1.975539
0.0 0.0 0.0 0.0
Coordinates are in atomic units (1au = 0.529177 A ) .
geometry determined by Ferronato et al.4 A partial geometry optimization was also carried out giving rC-H = 0.9278 A, rcx0 = 1.1125 A, and rC-F= 1.1262 A. Basch, Robin, and Kuebler15 and Snyder and Basch16 used a double basis set giving a total energy for formyl fluoride of -212.6841 hartrees and a dipole moment of 2.8 D. Snyder and Basch17give a computer output listing of the values of a number of one-electron properties obtained by using a double basis set without, however, any attempt at analysis of the results or at comparing them with experimental results. The calculation was carried out for the experimental geometry and no geometry optimization was attempted. Ditchfield et al.18 and Hehre and Poplelg have also carried out minimal basis set ab initio calculations on formyl fluoride. Klimek13 obtained a total energy of -212.8549 hartrees and dipole moments of pa = 0.21 D and pb = 2.41 D with a MCSCF procedure. No theoretical calculations on formyl chloride other than the semiempirical one by Frost et ala3are known to the writer. While a number of ab initio calculations have been carried out on formyl fluoride only one of these13 has involved full geometry optimization and, aside from determination of the dipole moment, only Snyder and Basch” and Bloor and Maksic20 have calculated one-electron properties. Even less theoretical work is available on formyl chloride. The purpose of this work is to carry out large basis set ab initio calculations on formyl fluoride and formyl chloride to determine their equilibrium geometries and some one-electron properties for these geometries and to compare and contrast the results obtained with available experimental data. This will provide a measure of the effectiveness of the basis sets used in predicting accurately molecular geometries and one-electron properties.
r
Method and Results The basis sets used for the calculations on formyl fluoride were of double quality, (13s 7p/4s 2p) contracted Gaussian type orbitals (CGTO) for the first row atoms and (6s/2s) CGTO’s for hydrogen.21 The same basis sets for the first row atoms and hydrogen were used in the formyl chloride calculations but the basis sets for chlorine were (17s 12p/4s 3p) CGTO’sa2lThe ab initio calculations were performed by using the IBMOLBA package developed by Clementi et a1.22 The one-electron property program is similar to that used in the POLYATOM/2 programs.23 All geometrical parameters in both molecules were optimized and the one-electron properties for the equilibrium geometries were calculated. Table I lists the principal Cartesian coordinates for the equilibrium geometries of both molecules with the positive direction of the a axis (y axis) pointing away from the oxygen to the halogen and the positive direction of the b axis ( x axis) pointing from the hydrogen to the carbon. Tables I1 and I11 give the optimized geometries, energies, and molecular orbital or-
r
TABLE 11: Geometry and Energies of Formyl Fluoridea b C d RC-H
Rc=o RC-F
LOCF
LHCO
1.069 1.189 1.365 121.0 128.5
1.089 1.213 1.379 122.2 126.9
Coulomb energy exchange energy nuclear attraction kinetic energy nuclear repulsion electronic energy total energy - V/2T
1.100 1.183 1.341 122.7 129.0
170.1057 -23.7619 -638.7592 212.8643 66.8473 -279.5510 -212.7037 0.9996
Molecular Orbitals -26.3371 F,, -0.8028 n p ( n o ) -20.6472 O,, -0.7330 nFzya (nC0) -11.4860 C,, -0.7318 nF ( n o ) - 1.6751 U C - F -0,6502 nF 1.4972 U C - 0 -0.5734 “CO (nFzpz) -0.9333 UC-H -0.5364 n o (nF) a Energies are in hartrees, bond lengths in angstroms, This work. Reference 13. bond angles in degrees. Reference 6, experimental.
TABLE 111: Geometry and Energies of Formyl Chloridea
__
RC-H
Rc=o Rc-Cl iOCCl iHCO
b
C
1.073 1.191 1.886 122.5 127.5
1.096 1.188 1.760 123.55 126.5
Coulomb energy exchange energy nuclear attraction kinetic energy nuclear repulsion electronic energy total energy - Vi2T
341.5 123 -41.1787 - 1531.0304 572.8693 85.1078 - 657.8275 - 572.7197 0,9999
Molecular Orbitals -104.8497 Cl,, -1.1340 Cl,, -20.6686 O,, -0.8977 ~ c - 1 1 -11.4745 C,, -0.7370 “HCO - 10.5807 CI,, -0.6782 oc-Cl (no,px) -8.0489 Cl,pxy -0.6255 “occ1 -8.0450 C1,pz -0.4832 nclsPx --8.0448 C12p,y -0.4796 no,pxy -1.5202 u C - 0 --0.4794 nCl,pz a All energies are in hartrees, bond lengths in angstroms, bond angles in degrees. This work. c‘ Reference 2, experimental.
dering and assignments for formyl fluoride and formyl chloride, respectively. A number of center-of-mass-based, one-electron properties for both molecules are given in Table IV while Table V lists certain atom-centered, oneelectron properties for the two molecules. Table VI gives the quadrupole coupling constants for the isotopic species containing 2H, I7O, and 350 by using the nuclear quadrupole moments of these atoms and the calculated electric field gradient centered on those atoms. Discussion A comparison of the optimized geometry of formyl fluoride with the results obtained by Klimek13 by using
The Journal of Physical Chemistry, Vol. 83, No. 25, 1979
3278
Tyrrell
TABLE IV: One-Electron, Center-of-Mass Properties for Formyl Fluoride and Formyl Chloridea formyl fluoride Y
X
potential nuclear electronic electric field nuclear electronic field gradient nuclear electronic dipole moment nuclear electronic quadrupole moment nuclear electronic second moment ( r 2 ) nuclear electronic octupole moment nuclear electronic diamagnetic suscept. nuclear electronic magnetic shielding nuclear electronic a
7.0232 -2.7076
--formyl chloride 2
15.2944
14.9352 - 14.3008
2.2710 -0.7742
0.0 0.0
6.5478
11.1092
5.4686
- 0.5485
- 4.9201
1.55 00 0.4167
-1.0783 1.3162
22.8763 26.0433
67.6652 -72.7007
--
0.7629
-1.7400 1.6523
- 0.4677
2.9129 -1.9467
- 6.6106
0.0 0.0
-1.5093 0.4043
-1.7365 1.6712
-44.7889 46.6574
-34.2111 38.6174
122.4204 -128.2762
7.4896 19.4930
-
14.1974 25.0346
75.3805 -91.6084
6.6861 -4.0040
- 7.8178
-
8.6084
0.0 0.0
3.6977 -2.5503
4.4970
89.5779 -128.3070 -24.8236 24.7218
2
- 13.2804
- 17.6569 --
Y
X
0.0 0.0 - 88.2094
89.6588
176.4187 -- 233.3095
0.0 0.0
-27.6475 25.7847
-138.6838 154.4917
0.0 0.0
0.0 -11.6641
16.2653 -33.1623
160.1534 -182.1499
0.0 -17.9973
1.3422 2.1365
13.5929 - 10.8621
0.0 -1.3022
0.0 ;1.4586
-
All units are atomic units,
TABLE V : One-Electron, Atom-Centered Properties for Formyl Fluoride and Formyl Chloridea formyl fluoride
H potentia~b electric field Ex E, field gradient 4xx QYY
Yzz
0 -27.3392
-8.3922
C -22.0392
-0.1149 0.0099
-0.0467 0.0241
0.1321 -0.2023
-0,3573 0.1765 0.1809
0.6061 -0.1658 -0.4403
2.1928 -0.6501 -1.5426
formyl chloride
F -31.0465
H
C
0 -28.4834
c1 -67.8562
-9.6479
-23.3266
0.0882 0.1750
-0.1065 -0.0085
-0.0483 -0.0359
0.1564 -0.1812
0.0235 0.0684
1.9020 -3.2159 1.3139
-0.3488 0.1737 0.1751
-
0.5909 0.1798 -0.4111
2.2566 -0.5925 -1.6641
2.3650 -4.3729 2.0079
diamagnetic shielding 0 dav
-148.96
-391.20
-485.27
-551.07
-171.25
-414.05
-505.58
-1204.45
All quantities except odav are in atomic units, odav values are expressed in ppm. Values listed for potential are electronic contribution only. Electric field and field gradients are sum of nuclear and electronic contributions. a
TABLE V l : Quadrupole Coupling Constants (- eqQ/h)a formyl fluoride formyl chloride aa bb CC aa bb CC 'H -0.116 0.235 -0.119 -0.114 0.229 -0.115 l7O --3.67 12.37 -8.70 -3.34 12.73 -9.39 3 5 c 1 -74.00 40.02 33.98
_ _ I -
. x _ _ _ -
a Units are megahertz. QzH -0.024b, Q35~1= -0.072b.
= -t 0.0027965 b,
Q170
=
MCSCF procedures and with the experimental results of LeBlanc et ala6shows quite good agreement with experiment. The results for the C-F and C=O bond distances are in better agreement with experiment than the MCSCF results while the opposite is true for the C-H bond distance. A calculation on formyl fluoride with the experimental geometry gave a total energy of -212.7024 hartrees, only slightly higher than the equilibrium geometry value of -212.7037 hartrees. The molecular orbital ordering is identical with that found by Czismadia14and by Klimek13 with a nonbonding oxygen orbital being the highest occupied followed by trco orbital. It should be noted that both these orbitals have significant fluorine contributions.
The optimized geometry of formyl chloride disagrees in only one significant point from the experimental geometry2 in that the C-C1 bond distance comes out much longer than the experimental value. Calculations on formyl chloride with a 4-31G basis set and the GAUSSIAN 70 program24give a similar optimized geometry with C-C1 bond distance of 1.847 A and a total energy of -572.1077 hartrees. If the experimental geometry is used with the large basis set a total energy of -572.7133 hartrees is obtained. Inclusion of d orbital character in the chlorine basis set would probably improve this result. The orbital ordering in formyl chloride is somewhat different from that in the fluoride particularly for the highest occupied orbitals. Using the optimized geometry one finds that the ordering indicates the two highest occupied orbitals are nearly degenerate with a nonbonding, out-of-plane chlorine 3p orbital slightly higher in energy than an orbital which is nominally nonbonding oxygen but has significant chlorine 3p character. This order is reversed when the experimental geometry is used in agreement with the assignment of the photoelectron s p e c t r ~ m but , ~ the two highest occupied orbitals are still nearly degenerate. The photoelectron spectrum analysis suggested, however, that the chlorine
Ab Initlo Calculations of HCOF and HCOCl
3p, and 3p,, nonbonding orbitals were nearly degenerate and significantly different in energy from the nonbonding oxygen orbital, The present calculations indicates that the the three highest occupied orbitals which are all nonbonding are of very similar energy. The CNDO/BW calculation on formyl chloride by Frost et al.3 predicted a u type orbital a t higher energy than the TCO orbital but these workers felt compelled to reverse this ordering in their interpretation of the photoelectron spectrum and the present calculation supports that decision. The present calculated values for the dipole moment components of formyl fluoride give pa = 0.605 D in excellent agreement with the experimental value, Ipal = 0.59E D, and indicating the fluorine to be somewhat positive and the oxygen negative in terms of electron distribution. Klimek,13using the MCSCF procedure, obtained pa = 0.47 D by using the experimental geometry and pa = 0.21 D by using the “best” geometry but with identical orientation. The value of & in the present calculation is -2.88 D compared to Klimek’s13“best” geometry value of 2.41 D. The sign difference is due to differing axis direction since both indicate the hydrogen to be the positive end of the dipole. Both values are somewhat higher than the experimental value for IpbI of 1.93 D. The experimental values for lpal and lpbl in formyl chloride are, respectively, 0.3 and 1.6 D and are to be compared with the present calculated values of pa = -0.166 D and p b = 2.809 D. This indicates that in formyl chloride the positive end of the dipole component pa is toward the oxygen in opposition to the situation in formyl fluoride. However, using the experimental geometry one finds pa = +0.338 D and &, = -2.644 D in better numerical agreement with the experimental values and in agreement with the dipole orientation in formyl fluoride. Obviously, the much longer C-C1 bond length found in the equilibrium geometry inhibits delocalization of the chlorine electron population. This can be observed in a general decrease in the magnitude of most of the orbital contributions to the electronic component of pa in the experimental geometry as compared to the equilibrium geometry. However, the effect on the nuclear contribution to pa of the C-C1 bond length difference is even more obvious and is in fact primarily responsible for the sign change. Rock, Hancock, and Flygarell experimentally determined the quadrupole moments of formyl fluoride to be 8ao = -4.5 x esu cm2, 8bb = 2.6 x esu cm2, and dcc = 1.9 X esu cm2. The calculated values of -6.77 x 4.26 x and 2.51 x esu cm2 for daa, e b b , and 8,,, respectively, are of the same sign and order of magnitude as the experimental values. No experimental quadrupole moments are available for formyl chloride but the calculated values of -7.88 X (-7.74 X 5.93 X (5.45 X and 1.95 X (2.29 X lowz6)for d,,, e b b , and Bo, respectively, where the values in parentheses are for the experimental geometry and are similar in sign and magnitude to the quadrupole moments in formyl fluoride. The components of the second moments of the charge distribution with respect to the center of mass in formyl fluoride were determined by Rock et al.ll to be 24.4 X lo4, 6.4 X and 2.6 X cm2for ( a 2 ) , ( b 2 ) ,and (c2), respectively. This gives a value of (r2)CM of 33.4 X cm2which compares well with the present calculated value for the electronic contribution to ( r2)CM of -35.93 X cm2, taking into account that Rock et al.’sl’ choice of direction of their principal axis is opposite to the ones used in this work. The calculated value for the for formyl chloride is electronic contribution to ( r 2 ) C M cm2 (-61.3 X cm2)where again the value -65.3 X in parentheses is for the experimental geometry indicating
The Journal of Physical Chemistry, Vol. 83, No. 25, 1979 3270
a more tightly bound electronic charge distribution for the experimental geometry. No experimental data are available for octupole moments for either molecule but the Y for completeness. results are listed in Table J The calculated electronic contribution to the second moment of the charge distribution can be used to determine the average diamagnetic susceptibility, xdaV, of the molecule by using the relation
xdav= ( - e 2 N / 6 m c 2 ) ( r 2 ) ~ ~ This results in a value of 102.4 X lo4 cm3/mol for formyl fluoride in good agreement with the experimental value’l of -94.4 X lo4 cm3/mol, again keeping in mind the respective choice of axes directions. The average diamagnetic susceptibility for formyl chloride is calculated to be 186.04 X lo* cm3/mol (174.6 X lo4 cm3/mol), the value in parentheses being that for the equilibrium geometry. Using the electronic contribution to the potential calculated at a specific atom in the molecule, one can determine the average diamagnetic shielding a t that atom in the vapor phase from the relation uda,(A) = (e2/3mc2)(l/r)A
where udav(A)is the average diamagnetic shielding at atom A in parts per million and ( l / r ) * is the toal electronic contribution to the potential at atom A in atomic units. The results for the average diamagnetic shielding at the atoms in the two molecules (Table V) indicate significant differences in the shielding at the hydrogen, carbon, and oxygen nuclei in formyl fluoride as compared to formyl chloride. Generally theories of chemical shifts in molecules assume that they arise primarily from changes in the paramagnetic terms. The present results are in agreement with other recent calculation^^^ in suggesting that diamagnetic effects may also play a significant part in determining chemical shifts. For an exact Hartree-Fock wave function the Hellman-Feynman theorem predicts that the sum of the forces on all the nuclei should be zero for all internuclear distances.26 The net force on each nuclei should be zero for the equilibrium geometry determined by using an approximate Hartree-Fock wave function which is fully optimized. From the values for the electric field components listed in Table V it is obvious that the Hellman-Feynman theorem is not satisfied for either molecule. The sum of the forces on all the nuclei is 1.2 X and 9.2 X 10”’ dyn along the positive x and y directions, respectively, for and -6.6 X dyn along formyl fluoride and 1.0 X the positive x and y directions for formyl chloride. The nonzero forces found at the individual nuclei indicate that the wave function is not completely optimized and the deviation of the wave functions from exact Hartree-Fock functions is indicated by the fact that the sum of forces on all nuclei differs from zero. The quadrupole coupling constants (-eqQ/h) for formyl fluoride and formyl chloride listed in Table VI can be determined knowing the appropriate nuclear quadrupole moments and electric field gradient at that nucleus. Kukolich12experimentally obtained the deuteron coupling constant in DCOF with a value of 205 kHz along the D-C bond direction. Using the value for QD and the field gradient a t the deuteron in the xx direction which approximates closely the D-C direction, one obtains a calculated value of 234.8 kHz. Ditchfield2’ obtained a value for the deuteron coupling constant in formyl fluoride of 216 kHz by using a 4-31 G basis set but with a standard geometrical model2s which makes comparison with the present result difficult. Because of the sensitivity of the
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25, 1979
deuteron coupling constant to bond length and the discrepancy between the optimized and the experimental C-H bond length the difference between the calculated and experimental deuteron coupling constant for formyl fluoride is not unexpected. The 35Clquadrupole coupling constants for formyl chloride given in Table VI should be compared with the experimental values obtained by Takeo and Matsumura2 for HC035C1. The experimentally determined values for (-eqQ/h),,, (-eq&h)bb,and (-eqQ/h),, are, respectively,--50.9,30.07, and 20.83 MHz. The electric field gradient at the chlorine is dominated by the electronic contributions and particularly those of the highest occupied molecular orbitals which would be expected to contain the largest inaccuracies and as a result good agreement between theory and experiment for the 35Clquadrupole coupling constants in formyl chloride would not be expected. In contrast the field gradient at the hydrogen in formyl fluoride contains a large nuclear contribution and little contribution from the other occupied molecular orbitals and good agreement between theory and experiment is expected and obtained. In conclusion there is, in general, good agreement between theory and experiment for the equilibrium geometries and one-electron properties of formyl fluoride and formyl chloride. The one major disagreement, the length of the C-C1 bond in formyl chloride, may indicate a need for a chlorine basis set including d-type Gaussian type orbitals.
References and Notes (1) I.C. Hisatsune and J. Heicklen, Can. J. Spectrosc., 18, 77 (1973). (2) H. Takeo and C. Matsumura, J. Chem. Phys., 04, 4536 (1976). (3) D. C. Frost, C. A. McDowell, and N. P. C. Westwood, Chem. Phys. Left., 51, 607 (1977). (4) E. Ferronato, L. Grifons, A. Guarniere, and G. Zuliani, Adv. Mol. Spectrosc., 3, 1153 (1962).
Hamnett et al. (5) R. F. Miller and R. F. Curl, J . Chem. Phys., 34, 1847 (1961). (6) 0. H. LeBlanc, V. W. Laurie, and W. D. Gwinn, J. Chem. Phys., 33, 598 (1960) (7) P. Favero, A. M. Mirri, and J. G. Baker, Nuovo Cimenfo, 17, 740 (1960). (8) P. Favero, A. M. Mirri, and J. G. Baker, J . Chem. Phys., 31, 586 (1956). (9) M. E. Jones, K. Hedberg, and V. Schomaker, J. Am. Chem. SOC., 77, 5278 (1955). (10) R. F. Stratton and A. H. Nielson, J. Mol. Spectrosc., 4, 373 (1960). (1 1) S.L. Rock, J. K. Hancock, and W. H. Flygare, J . Chem. Phys., 54, 3450 (1971). (12) S. G. Kukolich, J. Chem. Phys,, 55, 610 (1971). (13) D. E. Klimek, Ph.D. Dissertation, University of Wisconsin, Madison, Wisc., 1975. (14) I.G. Czismadia, M. C. Harrison, and B. T. Sutcliffe, Theor. Chim. Acta, 0, 217 (1966). (15) H. Basch, M.B. Robin, and N. A. Kuebler, J. Chem. Phys., 49, 5007 (1968). (16) L. C. Snyder and H. Basch, J. Am. Chem. Soc., 91, 2189 (1969). (17) L. C. Snyder and H. Basch, “Molecular Wave Functions and Properties”, Wley-Interscience, New York, 1972. (18) R. Ditchfield, J. Del Bene, and J. A. Pople, J. Am. Chem. Soc., 94, 703 (1972). (19) W. J. Hehre and J. A. Pople, J . Am. Chem. Soc., 92, 2191 (1970). (20) J. E. Bloor and 2. B. Maksic, J. Chem. Phys., 57, 3572 (1972). (21) S. Huzinaga and Y. Sakai, J . Chem. Phys., 50, 1371 (1969). (22) E. Clementi, J. Mehl, and H. Popkie, IBMOL5A User’s Guide, IBM Research Laboratory, San Jose, Calif. 95193. (23) D. B. Neumann, H. Basch, R. L. Kornegay, L. C. Snyder, J. W. Moskowitz, C. Hornback, and S. P. Liebmann, QCPE No. 199, The Polyatom (Version 2) Systems of Program for QuantitativeTheoretical Chemistry. (24) W. J. Hehre, W. A. Lathon, R. Ditchfield, M. D. Newton, and J. A. Pople, QAUSSIAN 70, QCPE No. 236, Quantum Chemistry Program Exchange, Indiana University, Bloomington, Ind. (25) W. H. Flygare, ”Magnetic Interactions and the Electronic Structure of Diamagnetic Molecules” in “Critical Evaluation of Chemical and Physical Sbuctural Information”, D. R. Lide and M. A. Paul, Ed., National Academy of Sciences, Washington, D.C., 1974. (26) C. W. Kern and M. Karplus, J. Chem. Phys., 40, 1374 (1964). (27) R. Ditchfield in “Critical Evaluation of Chemical and physical Structural Information”, D. R. Lide and M. A. Paul, Ed., National Academy of Sciences, Washington, D.C., 1974, p 578. (28) J. A. Pople and M. S. Gordon, J . Am. Chem. Soc.,89, 4253 (1967).
Photosensitization of Titanium(1V) Oxide with Tris(2,2’-bipyridine)ruthenium(II) Chloride. Surface States of Titanium( IV) Oxidet A. Hamnett, M. P. Dare-Edwards, R. D. Wrlght, K. R. Seddon, and J. B. Goodenough” Inorganic Chemistry Laboratory, Oxford OX1 30R, England (Received Aprll5, 1979)
Investigation of the photosensitization of single-crystalTiOz by [Ru(bpy),]Clz (where bpy = 2,2’-bipyridine) has revealed the existence of a slow-rise-timecathodic photocurrent in addition to the fast-rise-time anodic photocurrent reported by Clark and Sutin. Phenomenological analysis of the experiment provides a satisfactory quantitative explanation based on a modulation of an ongoing dark current by energy transfer from the dye to the solid. Two new experiments and an extensive literature implicate surface Of ions as the molecular species responsible for the slow kinetics. Some implications of these results for the photoelectrolysis of water by sunlight are also indicated.
Introduction In 1972, Fujishima and Honda’ reported that a singlecrystal, n-type TiOz anode is “chemically stable” when activated by UV light to oxidize water to oxygen. The “energy crisis” and the high cost of single-crystalsolar cells had already awakened interest in the possibility of using semiconductor electrodes to photoelectrolyzewater directly with sunlight, and two relevant facts were quickly established? (1)a polycrystalline Ti02anode is as efficient and + A Contribution from the Oxford-Imperial Energy Group. 0022-3654/79/2083-3280$01 .OO/O
stable as a single-crystal TiOz anode for the oxidation of water to O2 and (2) at the optimum photon wavelength, Hz evolution at a platinum counterelectrode in an electrolyte purged of oxygen is 10 times more efficient if an n-type SrTi03anode is used. Since the electron affinity, x,of SrTi0, was also shown to be 0.2 eV smaller than that of TiOz, the energy-diagram model of Figure 1 for pH 0 was put f o r ~ a r dnot ~ , only ~ to account for these observations but also to provide a strategic map for the design of a better anode. In the cell modeled in Figure 1, the two electrodes are connected by a short circuit and the metallic 0 1979 American
Chemical Society
