A DC9 FO TURNS THE WRONG WAY AFTER ATC ASSIGNS A TURN TO A HDG TO AVOID DSNDING TFC.

Narrative

AFTER STATION PASSAGE OF PXV AND ON AN INTERCEPT HDG OF THE OUTBOUND 048 DEG RADIAL; ATC REQUESTED A 20 DEG TURN FOR DSNDING TFC. AS FO; I WAS FLYING THE DC9 AND THOUGHT HE HAD DIRECTED A 20 DEG R TURN; SO I TURNED R. THE CAPT AND I STARTED LOOKING FOR THE TFC. THE TCASII SHOWED AN ACFT TO THE R AND ABOVE DSNDING. ATC THEN ASKED US IF WE HAD MADE A R TURN. WE SAID YES. I THEN ASKED THE CAPT IF WE WERE TO HAVE TURNED L AND IF I HAD MISUNDERSTOOD. HE SAID HE THOUGHT SO. ATC THEN TOLD THE OTHER ACFT TO EXPEDITE HIS DSCNT THROUGH FL330. HE THEN TOLD ME TO INITIATE A RAPID CLB TO FL350. AT THIS TIME TCASII SHOWED THE ACFT PASSING 2-5 NM TO OUR R AND APPROX 900-1200 FT BELOW OUR ALT. WE GOT A YELLOW TARGET WITH 1 'TFC' CALL. AS I WAS PASSING FL340 AT ABOUT THIS TIME; ATC TOLD ME TO RETURN TO FL330. I DID; STILL ON THE ORIGINAL HDG I HAD TURNED TO (060 DEGS). EVIDENTLY; I HAD TURNED R 20 DEGS RATHER THAN L 20 DEGS; BUT ATC DID NOT CHANGE MY HDG AND I WAS WONDERING WHY I HAD INITIATED A CLB. NO FURTHER MANEUVERS WERE REQUESTED BY ATC.