I can only find evaluations/rankings for departments such as chemistry or physics, but I am not sure how to evaluate a combined program of chemical physics.
To evaluate the strength of the program, you need to know chemical physics at professor level. If you are an incoming graduate student, you could try to see where the alumni end up. It's not easy, because not all the departments feel comfortable sharing that information, but you can get such information from the research groups' websites. As a rule, if people get strong academic or industry jobs doing research in chemical physics, it means it's a good academic program.
Departments also like to brag about their faculty getting large grants or joining large projects, about endowment, and research groups enjoy posting on their websites their latest published research results. If their work is highly cited, that's a good sign. Generally, if a program is strong, some of the faculty and even students obtain research prizes or fellowships. Another indirect way of telling is if these people have frequently invited famous speakers for seminars.
Still, if you want to apply to a program and you are in doubt about it, you could ask a faculty or a postdoc from the field of your interest for an opinion. Their opinion would probably be more useful than my answer here. Plus, even if you know for sure a program is good, there is no guarantee you'd find the research group that's best for you.