Feb 24 (Reuters) - Overview -- We expect operating results at U.S.-based chemical company American Pacific Corp. to support an improved financial profile in line with higher ratings. -- We are raising our corporate credit rating on American Pacific to 'B' from 'B-'. -- We are also raising our issue-level rating on the company's senior unsecured notes to 'B' from 'B-'; the recovery rating remains unchanged at '4'. -- The outlook is stable, reflecting our expect