Nonadiabaticity and the competition between alpha and beta bond fission upon 1[n,π*(C=O)] excitation in acetyl‐ and bromoacetyl chloride
1.The development of statistical transition state theories is reviewed by K. J. Laidler and M. C. King, J. Phys. Chem. 87, 2657 (1983).
2.The current status of statistical transition state theory is reviewed by D. G. Truhlar, W. L. Hase, and J. T. Hynes, J. Phys. Chem. 87, 2664 (1983).
3.P. J. Robinson and K. A. Holbrook, Unimolecular Reactions (Wiley-Interscience, London, 1972).
4.See extensive references in R. D. Levine and R. B. Bernstein, Molecular Reaction Dynamics and Chemical Reactivity (Oxford University, New York, 1987), Sec. 5.6, pp. 296–299.
5.P. A. Schulz, Aa. S. Sudbo, D. J. Krajnovich, H. S. Kwok, Y. R. Shen, and Y. T. Lee, Annu. Rev. Phys. Chem. 30, 379 (1979).
6.F. F. Crim, Annu. Rev. Phys. Chem. 35, 657 (1984).
7.For a review, see T. Uzer, Phys. Rep. 199, 73 (1991).
8.(a) L. J. Butler, E. J. Hintsa, S. F. Shane, and Y. T. Lee, J. Chem. Phys. 86, 2051 (1987);
8.(b) L. J. Butler, E. J. Hintsa and Y. T. Lee, J. Chem. Phys. 84, 4104 (1986)., J. Chem. Phys.
9.(a) R. L. Vander Wal, J. L. Scott, and F. F. Crim, J. Chem. Phys. 92, 803 (1990);
9.(b) N. Shafer, S. Satyapal, and R. Bersohn, J. Chem. Phys. 90, 6807 (1989) shows that preferential fission of the O–H bond even occurs from the ground vibrational state at 157 nm. This is because the larger zero point motion in the O–H bond results in better Franck-Condon overlap with the scattering wave function in the exit channel; , J. Chem. Phys.
9.( c) see also I. Bar, Y. Cohen, D. David, S. Rosenwaks, and J. J. Valentini, J. Chem. Phys. 93, 2146 (1990).
10.(a) Utilizing overtone excitation to access a different region of an excited electronic state appears early in L. J. Butler, T. M. Ticich, M. D. Likar, and F. F. Crim, J. Chem. Phys. 85, 2331 (1986);
10.(b) theoretical application to HOD is in J. Zhang, D. G. Imre, and J. H. Frederick, J. Phys. Chem. 93, 1840 (1989)
10.and in V. Engel and R. Schinke, J. Chem. Phys. 88, 6831 (1988).
11.D. Krajnovich, L. J. Butler, and Y. T. Lee, J. Chem. Phys. 81, 3031 (1984).
12.A preliminary communication on the acetyl chloride work appears in M. D. Person, P. W. Kash, and L. J. Butler, J. Phys. Chem. 96, 2021 (1992).
13.A preliminary communication on the bromoacetyl chloride work appears in M. D. Person, P. W. Kash, S. A. Schofield, and L. J. Butler, J. Chem. Phys. 95, 3843 (1991).
14.See also J. S. Keller, P. W. Kash, E. Jensen, and L. J. Butler, J. Chem. Phys. 96, 4327 (1992).
15.J. G. Calvert and J. N. Pitts, Jr., Photochemistry (Wiley, New York, 1966), Chap. 5.
16.Maintaining a bent geometry of the product as in Ref. 18.
17.(a) P. Ho, D. J. Bamford, R. J. Buss, Y. T. Lee, and C. B. Moore, J. Chem. Phys. 76, 3630 (1982);
17.(b) at higher energies, dissociation occurs via ISC to as seen in M. Chuang, M. F. Foltz, and C. B. Moore, J. Chem. Phys. 87, 3855 (1987).
18.J. Michl and V. Bonačić-Koutecký, Electronic Aspects of Organic Photochemistry (Wiley, New York, 1990), p. 378;
18.(b) ibid., p. 276. The treatment in this paragraph closely follows the beginning of the discussion in Michl for exciton coupling;
18.(c) see ibid., p. 276. and D. M. Silver, J. Am. Chem. Soc. 96, 5959 (1974).
19.A. K. Chandra, J. Mol. Struct. Theochem. 181, 255 (1988).
20.See a review of α cleavage in carbonyl compounds in M. Reinsch and M. Klessinger, J. Phys. Org. Chem. 3, 81 (1990) and extensive references within.
21.A notable exception is the evidence for an excited singlet pathway for C‐C cleavage in the t-butyl alkyl ketones in N. C. Yang and E. D. Feit, J. Am. Chem. Soc. 90, 504 (1968).
22.See, e.g., reviews in P. A. Schulz, Aa. S. Sudbo, D. J. Krajnovich, H. S. Kwok, Y. R. Shen, and Y. T. Lee, Annu. Rev. Phys. Chem. 30, 379 (1979).
23.F. F. Crim, Annu. Rev. Phys. Chem. 35, 657 (1984).
24.J. A. Devore and H. E. O’Neal, J. Phys. Chem. 73, 2644 (1969).
25.H. M. Rosenstock, K. Draxl, B. W. Steiner, and J. T. Herron, J. Phys. Chem. Ref. Data 6, Suppl. 1, I-774 (1969).
26.The universal detector was introduced by Y. T. Lee, J. D. McDonald, P. R. LeBreton, and D. R. Herschbach, Rev. Sci. Instrum. 40, 1402 (1969).
27.For details, see M. D. Person, Ph.D. thesis, Department of Chemistry, University of Chicago, 1991.
28.The only other study of acetyl chloride photolysis cited in the literature is work in the 1960s by W. D. Capey, J. R. Majer, and J. C. Robb, J. Chem. Soc. B 1968, 447, which postulated the dominant photochemical reactions involved molecular elimination processes with the loss of CO or O.
29.See K. Yates, S. L. Klemenko, and I. G. Csizmadia, Spectrochim. Acta Part A 25, 765 (1969).
30.In J. A. Barltrop and J. D. Coyle, Excited States in Organic Chemistry (Wiley, New York, 1975),p. 180, the C‐Cl fission in acetyl chloride is given as an example of cleavage of the weaker of the two alpha bonds. Although our work here shows the C‐Cl bond does cleave, the only experimental reference Barltrop and Coyle gave (Ref. 28 above) concluded that the dominant photochemical reactions involved loss of CO or O, not C‐Cl cleavage. In addition, C‐Cl cleavage should not be cited as an example of fission of the weaker alpha bond, as the C‐Cl bond is at least as strong as the C‐C bond.
31.R. N. Zare, Mol. Photochem. 4, 1 (1972).
32.G. Hancock and K. R. Wilson, Proceedings of the Fourth International Symposium on Molecular Beams, Cannes, France, 1973.
33.L. D. Waits, R. J. Horwitz, and J. A. Guest, Chem. Phys. 155, 149 (1991).
34.S. S. Hunnicutt, L. D. Waits, and J. A. Guest, J. Phys. Chem. 93, 5188 (1989);
34.S. S. Hunnicutt, L. D. Waits, and J. A. Guest, 95, 562 (1991)., J. Phys. Chem.
35.G. H. Dieke and G. B. Kistiakowsky, Phys. Rev. 45, 4 (1934).
36.N. Ohtomo and K. Arakawa, Bull. Chem. Soc. Jpn. 53, 1510 (1980).
37.The expression is given in G. E. Busch and K. R. Wilson, J. Chem. Phys. 56, 3638 (1972);
37.S.-C. Yang and R. Bersohn, J. Chem. Phys. 61, 4400 (1974)., J. Chem. Phys.
38.Because the C‐Br bond energy is not known for bromoacetyl chloride, we quote here and use elsewhere a typical bromoalkane C‐Br bond energy. However, when the C‐Br bond breaks in bromoacetyl chloride, the radical has two resonance structures, lowering the energy of the products below that for simple C‐Br bond fission.
39.P. W. Kash, G. C. G. Waschewsky, and L. J. Butler (to be published).
40.O. Steinnes, Q. Shen, and K. Hagen, J. Mol. Struct. 66, 181 (1980);
40.J. R. Durig, H. V. Phan, and T. S. Little, J. Mol. Struct. 197, 187 (1989)., J. Mol. Struct.
41.The electronic states split into five components with strong spin-orbit coupling, all of which are repulsive in the C‐Br bond.
42.For an example of direct photodissociation on these repulsive surfaces, see G. N. A. van Veen, T. Baller, and A. E. de Vries, Chem. Phys. 92, 59 (1985);
42.W. P. Hess, D. W. Chandler, and J. W. Thoman, Jr., ibid., (in press).
43.D. J. Krajnovich, Ph.D. thesis, Appendix B, University of California, Berkeley, 1983.
44.We estimated the ionization cross section using the empirical relationship obtained in R. E. Center and A. Mandl, J. Chem. Phys. 57, 4104 (1972),
44. The atomic polarizabilities of 3.05 and for Br and Cl are given in T. M. Miller and B. Bederson, Adv. At. Mol. Phys. 13, 1 (1977).
45.Our forward convolution programs for the center-of-mass to laboratory frame transformations were adapted from the CMLAB programs written by the Y. T. Lee group.
46.A program modified from the Hase-Bunker RRKM program obtained originally from the Quantum Chemistry Program Exchange, Department of Chemistry, University of Indiana, catalog number QCPE-234.
47.K. Tanabe and S. Saeki, Bull. Chem. Soc. Jpn. 47, 2754 (1974).
48. is typical of simple bond fission; see S. W. Benson and H. E. O’Neal, Natl. Stand. Ref. Data Ser., Natl. Bur. Stand, No. 21 (1970).
49.The C‐Br fission in the ground electronic state is not represented precisely by a simple bond fission because of the resonance stabilization of the radical. Consequently, we should use a smaller A factor and a smaller bond dissociation energy; however, the correction would only cause us to estimate even more of a propensity for C‐Br fission.
50.This can be said for all simple bond fission reactions. Calculations by D. M. Hayes and K. Morokuma, Chem. Phys. Lett. 12, 593 (1972) show there is no exit channel barrier for C‐H bond fission in of formaldehyde.
51.H. Zuckermann, B. Schmitz, and Y. Haas, J. Phys. Chem. 92, 4835 (1988).
52.Joyce Guest (private communication)
53.P. Avouris, W. H. Gelbart, and M. A. El-Sayed, Chem. Rev. 77, 793 (1977).
54.E. K. C. Lee and R. S. Lewis, Adv. Photochem. 12, 1 (1980).
55.As we do not know the rotational temperature of the molecules in the expansion to high precision, the average rotational period is difficult to pin down, but we estimate it to be 1–10 ps (Ref. 32).
56.Although halogenated systems evidence strong spin-orbit coupling, we must reference to the LS coupling limit here to characterize the orientation of the Cl p orbital with respect to the C, plane of symmetry Under strong spin-orbit coupling in the excited states split into five components, each with mixed singlet/triplet character. Thus in acetyl-and bromoacetyl chloride, the avoided crossing is between the electronic configuration and the C‐Cl states in the strong spin-orbit basis which have a component of character.
57.M. B. Robin, Higher Excited States of Polyatomic Molecules III (Academic, New York, 1985), p. 26.
58.A. Gedanken and M. D. Rowe, Chem. Phys. Lett. 34, 39 (1975).
59.Chandra has previously considered the possibility of selective fission of the C‐Cl bond over the C‐C bond on the triplet surface. He argues that C‐C fission on the adiabatic triplet surface has a much higher energy barrier than C‐Cl fission (see Ref. 19).
60.The Franck-Condon region of the C-Cl surface occurs at higher energy (170 nm) (Ref. 58) than for the C‐Br configuration (205 nm), (Ref. 58) indicating that the point of intersection with the surface and therefore the barrier to C‐Cl fission is higher. (This assumes the avoidedness of the crossing on the adiabats does not contribute as much as the difference in energies of the diabats.)
61.M. Born and R. Oppenheimer, Ann. Phys. 84, 457 (1927).
62.The adiabatic assumption was discussed briefly in M. G. Evans and M. Polanyi, Trans. Faraday Soc. 31, 875 (1935)
62.and challenged by E. Rabinowitch in the discussion of the paper by M. G. Evans and M. Polanyi, Trans. Faraday Soc. 34, 11 (1938).
62.The following paper by E. Wigner, Trans. Faraday Soc. 34, 29 (1938) also discusses the adiabatic assumption.
63.(a) J. C. Tully, in Dynamics of Molecular Collisions Part B, edited by W. H. Miller (Plenum, New York, 1976), p. 217;
63.(b) This article includes one of the best reviews of nonadiabatic molecular collisions, noting that not only reactions involving electronically excited species and ion-molecule reactions can be nonadiabatic, but also reactions of ground state species at room temperatures.
64.A good introduction is given in L. Salem, Electrons in Chemical Reactions (Wiley-Interscience, New York, 1982).
65.The only mention of nonadiabaticity in molecular collisions in Ref. 4 is on p. 124 with regard to the harpoon mechanism and electronic energy transfer.
66.See also J. N. Murrell and S. D. Bosanac, Introduction to the Theory of Atomic and Molecular Collisions (Wiley, New York, 1989), Chap. 6
66.and M. Baer, The Theory of Chemical Reaction Dynamics, Vol. II (CRC, Boca Raton, FL, 1985).
67.At the introduction to transition state theory, Eyring did not introduce the transmission coefficient k to correct for nonadiabatic effects, but only to account for trajectories recrossing the transition state on a skewed potential energy surface. See W. F. K. Wynne-Jones and H. Eyring, J. Chem. Phys. 3, 492 (1935).
68.One of the first papers to correct a bimolecular reaction rate for adiabatic vs diabatic crossing was A. G. Evans and M. G. Evans, Trans. Faraday Soc. 31, 1400 (1935). They used Landau-Zener theory to correct the rate of reaction in the now well-recognized case of a reaction involving the crossing of ionic and covalent electronic states.
69.K. Q. Lao, E. Jensen, P. W. Kash, and L. J. Butler, J. Chem. Phys. 93, 3958 (1990).
70.L. J. Butler, D. Krajnovich, Y. T. Lee, G. Ondrey, and R. Bersohn, J. Chem. Phys. 79, 1708 (1983).
71.C. Mijoule, S. Odiot, S. Fliszar, and J. M. Schnur, J. Mol. Struct. Theochem. 149, 311 (1987).
72.See S. Hassoon, H. Lustig, M. B. Rubin, and S. Speiser, J. Phys. Chem. 88, 6367 (1984) and references within.
73.P. W. Kash and L. J. Butler, J. Chem. Phys. 96, 8923 (1992).
74.M. D. Person, P. W. Kash, and L. J. Butler, J. Chem. Phys. 94, 2557 (1991).
75.S. Yabushita and K. Morokuma, Chem. Phys. Lett. 175, 518 (1990).
76.S. Yabushita and K. Morokuma, Chem. Phys. Lett. 153, 517 (1988);
76.Y. Amatatsu, K. Morokuma, and S. Yabushita, J. Chem. Phys. 94, 4858 (1991).
77.M. Chattoraj, B. Bal, G. L. Closs, and D. H. Levy, J. Phys. Chem. 95, 9666 (1991).
78.G. L. Closs and J. R. Miller, Science 240, 440 (1988).
79.G. L. Closs, P. Piotrowiak, J. M. MacInnis, and G. R. Fleming, J. Am. Chem. Soc. 110, 2652 (1988).
80.This empirical expression applies only within a series which changes the number of intervening bonds without changing the conformation of the donor/acceptor pair. Thus, using this expression is only meant to give a qualitative feel for how much the coupling can change with increased separation.
81.W. H. Pence, S. L. Baughcum, and S. R. Leone, J. Phys. Chem. 85, 3844 (1981).
82.Development of the formal model, suggested by L. Butler, based on coupled repulsive diabatic states is in S. Das and D. J. Tannor, J. Chem. Phys. 91, 2324 (1989).
83.The qualitative reason for this given in Ref. 8(a) neglected the second term in the dipole-dipole coupling for far-separated dipoles, so is incorrect. Professor J. Simon suggested the difference in coupling might result from a better overlap between the σ* orbitals in 1,2- because of the trans orientation.
84.K. H. Fung and K. F. Freed, Chem. Phys. 30, 249 (1978).
85.R. B. Woodward and R. Hoffman, The Conservation of Orbital Symmetry (Chemie, Weinheim/Bergstrasse, 1970).
86.See, e.g., the calculations of E. Ottavianelli, E. A. Castro, and A. H. Jubert, J. Mol. Struct. Theochem. 165, 149 (1988).
87.See also footnote 11 on p. 36 of Ref. 85.
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