G. D. Fletcher, M. J. Alguard^*, T. J. Gay, V. W. Hughes, C. W. Tu^†, and P. F. Wainwright^‡

• J. W. Gibbs Laboratory, Yale University, New Haven, Connecticut 06520

M. S. Lubell

• J. W. Gibbs Laboratory, Yale University, New Haven, Connecticut 06520, and Physics Department, The City College of the City University of New York, New York, New York 10031

W. Raith

• J. W. Gibbs Laboratory, Yale University, New Haven, Connecticut 06520, and The University of Bielefeld, Bielefeld, Federal Republic of Germany

F. C. Tang

• Physics Department, The City College of the City University of New York, New York, New York 10031

• ^*Permanent address: Measurex Corporation, Cupertino, Cal. 95014.
• ^†Permanent address: Bell Laboratories, Murray Hill, N. J. 07974.
• ^‡Permanent address: Bell Laboratories, Holmdel, N.J. 07733.