Microwave spectra for the D-1 and D-6 isotopomers of (benzene)chromium tricarbonyl and (fluorobenzene)chromium tricarbonyl were measured using a Flygare-Balle type microwave spectrometer system. The new rotational constants for the deuterium-substituted isotopomers are used with previous data which include C-13 isotopomers to obtain a gas-phase structure for (benzene)chromium tricarbonyl. The new rotational constant for the C6D6, symmetric-top, isotopomer is B(bz-d(6)) = 698.6934(1) MHz. Asymmetric-top structure were observed for a single deuterium substitution on benzene, giving B(bz-d(1)) = 730.0391(4) MHz and C(bz-d(1)) = 723.6641(3) MHz. Rotational constants obtained for (fluorobenzene)chromium tricarbonyl are A = 814.1491(2) MHz, B = 641.1594(2) MHz, and C = 586.5866(1) MHz. The centrifugal distortion constants are small, with D-J congruent to 0.05 kHz. Structural parameters determined are center of the benzene carbon plane to chromium distance r(Cr-bz) = 1.66(2) Angstrom, the chromium to carbonyl carbon bond length r(Cr-CO) 1.876(7) Angstrom, the benzene carbon to hydrogen bond length r(C-H) 1.080(3) Angstrom, and the carbonyl carbon to oxygen bond length r(C-O) 1.148(7) Angstrom. The OC-Cr-CO interbond angle is a = 87.4(6)degrees. The average benzene C-C bond length is 1.413(3) Angstrom. A small isotopic shift in the Cr-53 quadrupole coupling strength was observed for the C6D6 isotopomer relative to the normal isotopomer. The hydrogen atoms are displaced out of the benzene carbon plane toward the Cr atom with the C-H bond axis at an angle gamma = 2.8(2)degrees with respect to the benzene carbon plane.