You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named (1R,2aS,8bS)-1-chloro-4-oxo-2,2a,3,8b-tetrahydrocyclobuta[c]isoquinoline-1-carbonitrile by IUPAC nomenclature, provide its molecular formula.
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C12H9ClN2O
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