What are the chances of getting into a great CS PhD program with research in a different field?
I'll assume you intend to study in the US. It might be a bit different elsewhere.
From the sound of it, you are a good and eager student, interested in opportunities. If your record is good, generally, and you get good letters of recommendation from professors, then you are competitive. However, there is a lot of competition, and the higher up you go in university rankings the fiercer it tends to get.
Only an admissions committee can really answer your question, and that would only be in how they treat your application. There are a lot of applicants for every slot in doctoral programs.
If you want to assure that you find something suitable, cast a wide, rather than a narrow net in making applications. Apply to a few &quot;dream&quot; universities, but also to some others that have good programs, but not necessarily in the top 25, or even 50 in the rankings. The worst case is that you will get a lot of offers with a wide net, but no offers at all with a narrow one. Stay flexible.
Some undergraduates going in to doctoral programs (in the US) have some research experience, but not all. The fact that you have some, even in chemistry, is a plus, but more for your overall likelihood of success.