MD88 FLT CREW ON DSCNT FOR PVD EXPERIENCED TCASII RA WITH ATC ISSUED VFR TFC.

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DURING DSCNT ON VECTORS TO PVD; WE WERE DSNDING TO 8000 FT MSL ASSIGNED. AS WE PASSED 9000 FT IN THE DSCNT; I SAW TFC AT 8500 FT ON TCASII FOLLOWED BY A TA. APCH SAID 'VFR TFC 1 O'CLOCK; 1 MI -- CLB OR DSND. WE WERE PASSING 8300 FT GOING DOWN. I INITIATED A CLB BASED ON HIS INITIAL CALL THINKING HE MIGHT HAVE SEEN THE TFC BEGIN TO DSND. THEN GOT AN RA COMMANDING DSCNT. PUSHED THE ACFT INTO AN IMMEDIATE DSCNT AND THE TCASII CLRED. APCH TURNED US L AWAY FROM TFC; BUT THE INCIDENT WAS OVER BY THIS TIME. WE NEVER HEARD ABOUT THE TFC UNTIL WE WERE FAR TOO CLOSE FOR; COMFORT. I DON'T KNOW IF APCH WAS TRACKING HIM BEFORE THEN BUT IF SO; WE SHOULD NEVER HAVE BEEN CLRED BELOW 9000 FT WITH VFR TFC AT 8500 FT. WE DID NOT VISUALLY ACQUIRE THE TWIN UNTIL THE DSCNT; WHICH SOLVED THE PROB. THE TCASII SAVED THE DAY. I FELT THAT A VERY QUICK TERMINATION OF CLB AND TRANSITION TO DSCNT HELPED ONCE THE RA WAS GIVEN SINCE OUR TRAINING INDICATES A 2 SECOND RESPONSE TIME AND WE PROBABLY WERE WELL INSIDE THAT. THE SPECIAL EVENT AT ZZZ WITH THE ACCOMPANYING AIRSPACE RESTRS PROBABLY ALSO CONTRIBUTED TO THE CTLR'S WORKLOAD. THE NOTAM/TFR WAS NOT LISTED ON MY FLT PLAN AND WE DID NOT FIND OUT ABOUT IT UNTIL AFTER THE EVENT.