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ilar fashion having nearly the same ~7and r ionization energies near 11.2 eV. Acknowledgments. One author, T. F., would like to acknowledge both the hospitality of the Physical Chemistry Laboratory at which this work was carried out and the support of the National Science Foundation (Grant No. G P 28320). We thank Dr. Robert Sams and Dr. Arthur Maki for communicating their work prior to publication. T. P. Fehlner* Department of Chemistry, Unicersity of Notre Dame Notre Dame, Indialla 46556
D. W. Turner Physical Chemistry Laboratory, Oxford Unioersity Oxford, Biglaud Receiced June 15, 1973
Comparison of Photochemical and Temperature- Jump Perturbations. The Rate of Interconversion of Planar and Octahedral Configurations of a Nickel(I1) Complex’
Figure 1. Absorbance at 440 nm as a function of time for solutions of NiLCI2 (L = NH2(CHz)zNH(CH2)sNH(CHs)2NH2), with initial temperature 23“. The initial light intensity level was one major division above the bottom of the photograph, and the absorbance increases along the vertical axis. (a) 1.06 p radiation, solvent HzO, initial440 nm absorbance is0.32 ([Ni(Il)] = 0.38 M : pathlength 0.08 cm), horizontal scale 0.2 psec per major division, vertical scale 2z absorbance change per major division; (b) 1.06 p radiation, solvent DnO, initial 440 nm absorbance is 0.21 ([NKII)] = 0.13 M . pathlength 0.16 cm), horizontal scale 0.2 psec per major division. vertical scale 3 % absorbance change per major division: (c) 1.41 p radiation, solvent HzO, initial 440 nm absorbance is 0.32 ([Ni(II)] = 0.38 M , pathlength 0.08 cm), horizontal scale 0.1 psec per major division, vertical scale 2 % absorbance change per major division; (d) 1.41 p radiation, solvent D 2 0 , initial 440 nm absorbance is 0.32 ([Ni(II)] = 0.38 M , pathlength 0.08 cm), horizontal scale 0.2 psec per major division, vertical scale 0.6% absorbance change per major division.
Sir: Pulsed neodymium lasers are finding increasing application in the study of fast chemical reactions. One such application is the temperature-jump technique in which the laser is used to raise the temperature of a solution containing the system of interest by several degrees within a very short time; this is conveniently accomplished by using a laser wavelength that is a b . hedral (3A2g)forms in aqueous solution at room tempersorbed strongly by the solvent, but not the solute^.^-^ at~re.~*8 In a less common application, the laser is used to NiL2+ + 2H20 NiL(H?O)12C (1 rapidly photochemically dissociate a reactant or convert it into a product of the reaction; in this case, the laser This reaction was previously found to be too rapid for frequency is chosen so that solvent absorption is at a study by conventional temperature jump techniques.s minimum but solute absorbance is highe5v6 Following The system’s relaxation times were, however, obtained these perturbations, the rate of adjustment of the system in a study employing the neodymium laser radiation to its new equilibrium position (relaxation rate) is (1.06 p) t o rapidly perturb the above equilibrium by followed. This rate provides information about the electronic excitation of the octahedral nickel complex kinetics obtaining in the system. We wish to report the ( ~ ~ . ~ -2.0 6 M-I cm-l>.j Following this perturbaresults of a rather novel kinetic study in which a neotion, the return of the system to equilibrium was mondymium laser was used t o produce predominantly either itored by the absorbance decrease at 440 nm (an abtemperature increases or concentration jumps in the sorbance maximum for the planar complex). We same equilibrium system depending upon whether the have repeated these measurements on solutions 0.1-0.4 wavelength of the laser radiation was 1.06 or 1.41 p M in the chloride salt (both in H 2 0 and D20) using and the solvent HzO or DzO. In each case the subsecells with path lengths of 0.08 and 0.16 cm. A typical quent relaxation of the system was followed spectrorelaxation is shown in Figure l(a). It should be noted photometrically. that there is a very rapid increase in the absorbance at The system chosen for study is the nickel(I1) complex 440 nm (rise time 30 nsec, the laser pulse width). This of the quadridentate ligand NH2(CH&NH(CH&,NH- is followed by a slower absorbance decrease. The re(CHs)*NH2 (N,N’-bis(2-aminoethyl)-l:3-propanedi- laxation time for this decrease is 0.30 i: 0.02 psec at 23 o amine).7 The nickel complex exists as an equilibrium and independent of the concentration of the nickel mixture of low-spin planar (lAIg) and high-spin octacomplex, in accord with the previously reported resu1ts.j Also noteworthy is the observation that the (1) Research performed under the auspices of the U. S. Atomic “infinite time” absorbance is greater than the initial abEnergy Commission. sorbance. This is due to a small displacement of the (2) J. V. Beitz, G. W. Flynn, D. H. Turner, a n d N. Sutin, J. Amer. Chem. Soc., 92,4130(1970). equilibrium resulting from the heating of the system. (3) D. H. Turner, G. W. Flynn, N. Sutin, and J. V. Beitz, J. Amer. This effect is smaller, but not absent, in D?O (Figure Chem. Soc., 94, 1554 (1972). (4) J. I
