Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
imperturbātus (inp-), a, um, adj. [2. in-perturbatus], undisturbed, unruffled, calm (very rare): imperturbato ore, Ov. Ib. 562: publicis occupationibus quies, Sen. Ep. 73 med.
Of persons: audio imperturbatus, interritus, Plin. Ep. 9, 13, 8: qui constans est, inperturbatus est, Sen. Ep. 85, 2; cf. ib. § 3.