| Summary: | We report on X-ray photoelectron spectroscopy (XPS) and ab initio electronic structure investigations of a novel intermetallic material Ce<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>9</mn> </msub> </semantics> </math> </inline-formula>Ru<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>4</mn> </msub> </semantics> </math> </inline-formula>Ga<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>5</mn> </msub> </semantics> </math> </inline-formula>. The compound crystallizes with a tetragonal unit cell (space group I4<inline-formula> <math display="inline"> <semantics> <mrow> <mi>m</mi> <mi>m</mi> </mrow> </semantics> </math> </inline-formula>) that contains three inequivalent Ce atoms sites. The Ce <inline-formula> <math display="inline"> <semantics> <mrow> <mn>3</mn> <mi>d</mi> </mrow> </semantics> </math> </inline-formula> core level XPS spectra indicated an intermediate valence (IV) of selected Ce ions, in line with the previously reported thermodynamic and spectroscopic data. The ab initio calculations revealed that Ce1 ions located at <inline-formula> <math display="inline"> <semantics> <mrow> <mn>2</mn> <mi>a</mi> </mrow> </semantics> </math> </inline-formula> Wyckoff positions possess stable trivalent configuration, whereas Ce2 ions that occupy <inline-formula> <math display="inline"> <semantics> <mrow> <mn>8</mn> <mi>d</mi> </mrow> </semantics> </math> </inline-formula> site are intermediate valent. Moreover, for Ce3 ions, located at different <inline-formula> <math display="inline"> <semantics> <mrow> <mn>8</mn> <mi>d</mi> </mrow> </semantics> </math> </inline-formula> position, a fractional valence was found. The results are discussed in terms of on-site and intersite hybridization effects.
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