趁着 and 趁 are interchangeable, but 趁着 is slightly more colloquial and emphasizes the ongoing nature of the opportunity. 趁热打铁 (strike while the iron is hot) always uses bare 趁.
grammar
趁着 + condition clause, main clause. The condition describes a favorable temporary situation: 趁着有空 (while there's free time), 趁着便宜 (while it's cheap).
