J. Phys. Chem. 1082, 86, 1503-1506
anharmonicity constants have been reported by Lucazeau and Sandorfy from the normal mode analysis of low-energy combination and overtone bands in acetaldehyde and acetaldehyde-dWl6 The present results may be better than those by Lucazeau and Sandorfy, since their evaluation of unperturbed frequencies ( A + B ) and anharmonicity constants is rather indirect and the calculated dissociation energies from their A and B values are in poor agreement with observed values (Table 11). Therefore, the low vibrational frequencies observed for the aldehydic CH stretchings appear to be due to a low harmonic frequency rather than to a high anharmonicity constant. Bond dissociation energies (De) were evaluated from Morse (M) and Lippincott-Schroeder (LS) potential functions and are given in Table 11. The following equations were used: D,(M) = -(A - B ) 2 / 4 B where A = we - w g e , B = wexe, and we and upeare har(16)G.Lucazeau and C. Sandorfy, Can. J. Chem., 48,3694 (1970).
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monic and anharmonic constants, and De(LS) = k , / [ ( 6 4 r 2cpw,3ce/3h) - l/r,2] where p is reduced mass of a CH bond, and re is equilibrium CH bond distance.” D,(LS) is calculated by setting k, = 4fc2w,2p l8and using the equilibrium distances in ref 7 and 10. It is noted that the predicted dissociation energies for the acetyl CH bonds are in reasonable agreement with the observed values as in the case of aromatic and alkyl CH bonds.6J3J8 The discrepancy between the observed values and the calculated ones on the basis of the Birge-Sponer extrapolation is about 20%, while the LippincottSchroeder model gives better agreement. (17)E. R. Lippincott and R. Schroeder, J. Chem. Phys., 23, 1131 (1956). (18)B. R. Henry, M. A. Mohammadi, and J. A. Thomeon, J. Chem. Phys., 75,3165 (1981). (19)K. W. Egger and A. T. Cocks,Helu. Chim. Acta, 56,1516(1973). (20)J. A. Kerr, Chem. Reu., 66,465 (1966).
Excitation of Cu Atoms by Energy Transfer from Vibratlonally Selected N,(A32,+, v ) I. Nadler, 0. Rawnitzkl, and S. Rosenwaks* Depertments of Fhyslcs and ChemlsW, BenGurion Unlverslty of the Negev, Beer-Sheva, Israel ( R e c e M : December 30, 198 1; I n Flnal Form: February 23, 1982)
Cu emission resulting from the reaction of copper atoms with N2(A,u=0,1,2)in a flowing afterglow apparatus is compared to that resulting from interaction of Cu with N2(A,u=O).The latter is obtained from vibrationally excited N2(A)by using “vibrational quenchers”. The dependence of the Cu excitation on the N2(A,ur-X,u’3 Franck-Condon factors and on the energy matches for the Nz(A,u9+ C U ( ~ S ~ / Nz(X,ur9 ~) + Cu* reaction is investigated.
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The study of quenching of N2(A3&+,u)by various molecules and atoms has been the subject of current In a recent study publications from several of the reaction of N2(A,u10)with Cu atoms in a flowing afterglow apparatus it was demonstrated that a nonBoltzmann population distribution of the Cu states is obtained.6 It was suggested that the distribution reflects the nearly resonant energy-transfer processes N~(A,u’) + C U ( ~ S ~ N~(X,U’’) ~) + CU* (1)
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and that the Franck-Condon factors (FCF) for the N2(A,v’-X,u ’9 transitions influence the efficiency of the processes. However, in that study, translationally hot Cu atoms were reacted with N2(A) distributed over the u = 0, 1 (and possibly 2) vibrational levels and the effects of energy match and FCF were smeared to some extent and could not be studied in detail. In the present study, the influence of the vibrational population of N2(A,u)is accounted for by comparing the emission from translationally cold Cu atoms that have reacted with N2(A,u10) and N2(A,u=O).By carefully analyzing the emission spectra, (1)W. G.Clark and D. W. Setser, J. Phys. Chem., 84,2225 (1980). (2)E. C. Zipf, Nature (London),287,523(1980). (3)L.G.Piper, G . E. Cdedonia, J. P. Kennedy, J. Chem. Phys., 74, 2888 (1981);75, 2847 (1981). (4)M. P.Iannuzzi and F. Kaufman, J. Phys. Chem., 85,2163 (1981). (5)I. Nadler and S. Rosenwaks, Chem. Phys. Lett., 69,266 (1980). 0022-365418212088-1503$01.25/0
the importance of the above-mentioned effects is clearly demonstrated. N2(A,u10)is produced in a flowing afterglow apparatus of standard design1 by the energy-transfer reaction Ar(3P0,2)+ N,(X); the N2(A,u=O)is obtained by relaxing N2(A,u21)via addition of CHI or CF4 downstream of the Ar* + N2 mixing zone. Both CHI and CF4 are known to vibrationally relax N2(A,u11)without significant electronic quenching.ly6 N2 (“oxygenfree”, 99.998%), Ar (99.997%), CH4 (Research Grade, 99.99%),and CF4 (99.7%)are used directly from the bottles. The Cu atoms are produced in a metal evaporation furnace,5J carried in an argon stream and mixed with the N2(A). The emission from the Cu atoms is o b s e ~ e d12 cm downstream from the mixing zone so that adequate time (-6 ms) ensurea good mixing of the reactants prior to their arrival in the observation region. The concentration of ground-state Cu atoms is evaluated via atomic absorption by using a Cu hollow cathode lamp. Since the argon carrier gas is in contact with the watercooled stainless steel walls of the flow system housing, the gas mixture in the observation region is maintained near room temperature (27-30 OC as measured by a thermistor immersed in the flow). The detection system consists of (6)I. Nadler and S. Rosenwaks, to be published. (7)J. B. West, R. S. Bradford, Jr., J. D. Eversole, and C. R. Jones, Rev.
Sci. Instrum., 46,164 (1975).
@ 1982 American Chemical Society
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The Journal of Physical Chemistry, Vol. 86, No. 9, 1982
Letters
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Flgure 1. Typical Cu emlssion spectra resulting from the N&A,v) Cu reaction. The resolution is 0.3 nm, the total gas pressure is 1.3 torr, and N,/Ar = 113. Intensities are not corrected for instrument Cu, (b) N,(A,v=O) Cu. The N,response. (a) N,(A,v=0,1,2) (A,v=O) is obtained by addlng 1.5% CH, downstream of the Ar' N, mixing zone. The Cu lines wtth the largest enhancement are marked by a f, those with the largest decrease by 1. Similar spectra are obtained by adding 6 % of CF, in place of CHI.
+
+
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a 0.3-m scanning monochromator with a grating blazed for 500 nm (first order), a thermoelectrically cooled photomultiplier tube, a picoammeter, and a strip chart recorder; the system is calibrated with a standard lamp. The vibrational distribution of the N2(A,u'=0,1,2) levels in the observation region is calculated by using the observed N2(A,uCX,u'? emission intensities, calibrated by the standard lamp, and published transition probabilities? and is found to be 1.0/0.75/0.25. The population of N2(A,u=3) is
