I was recently searching around on the Internet for some help with the Particular effect, and I found this thread over at Video Copilot.
http://www.videocopilot.net/forum/viewtopic.php?f=20&t=53280
Seems someone else is having the same trouble I am, with multiple Particular layers not working together and particles rotating after they've hit the wall. I don't know how this guy has his set up, but here's how I have mine:
With Particular, I have the Particle>Rotation>Random Rotation set to the number I want. Then I set the Physics to "Bounce," and set up all the fields for a wall and put the 3D wall layer into place, and then set Collision Event to "Stick."
So, like this guy at Video Copilot, I want the particles to stop spinning once they hit the wall. Is there a formula that I need to use for the particle rotation (something like "=#.if{z>wall's z value} else =0")?