Wash your pants in hot water with a cup of vinegar, and then run again in hot water with a half-cup of baking soda. (Do not add laundry detergent to either wash. Just once with vinegar and once with baking soda.)
Laying them in the sun will get the smell out but it won't get the residual chemicals out from the gas.

Have a heart that never hardens, a temper that never tires, a touch that never hurts. - Charles Dickens