I bought Tubular Bells on vinyl when it was first released, but for the life of me I can’t remember whether I first heard it before or after The Exorcist. Hazy time, I guess, I was 18 then. Regardless, I do not relate the music to the film, and I still listen to the album a lot. I saw the movie when it came out in '73. Saw it again recently and found it somewhat scary, but rather dated.
I heard Tubular Bells before the Exorcist. I had to buy the British import because it hadn’t been released in the states yet.
I went to see the Exorcist on the day it was released. I remember cracking up when the music started, saying “Hey, that’s Tubular Bells.”
As far as it being scary, I can never associate that with scary. Knowing it was the late, great Vivian Stanshall of the Bonzo Dog Band, (the band Eric Idle claims taught Monty Python to be silly) narrating it, hearing it as some sort of natural progression of “The Intro And The Outro”, there was just too much whimsy associated with it in my mind.
The hands-down scariest movie music is the Kyrie from the Requiem by Gyorgy Ligeti, in 2001: A Space Odyssey. I played that once out my window for Halloween and no kids ever came close to my house.
Orchestral Tubular Bells is great, BTW. I think there are numerous orchestral flubs in it, but the music itself is pretty good.