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We have investigated a palladium–hydrogen complex in silicon by electron spin resonance (ESR) measurement. A new ESR spectrum was detected in a sample diffused with palladium and hydrogen. The hyperfine structure of hydrogen atoms in the ESR spectrum shows that the spectrum originates from a palladium–hydrogen complex containing three hydrogen atoms (Pd–H3). The anisotropic g-value of Pd–H3 shows that the Pd–H3 complex has an anisotropic character of orthorhombic (C 2v ) symmetry. The calculated g-values of the Pd–H3 complex are g 1 = 2.12, g 2 = 2.10, and g 3 = 2.03, and the g 2 axis is along the <100 > direction. The anisotropic character of orthorhombic (C 2v ) symmetry results from a configuration consisting of one Pd atom at a substitutional site, two equivalent hydrogen atoms at interstitial sites along the <111 > direction, and one hydrogen atom at the next-nearest-neighbor interstitial site along the <100 >-twofold symmetry axis. We have also studied the dissociation of a platinum–hydrogen complex by thermal treatment. The activation energy for the dissociation of the Pd–H3 complex is estimated to be about 1.6 eV.

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