Apparent pressure shift of rotational transitions as a consequence of the unresolved hyperfine structure

Apparent pressure dependent shifting of the peak positions of rotational lines, which is a consequence of unresolved hyperfine structures, is analyzed. In addition, possible line profile asymmetries and their influences on the ultimately achievable measurement accuracy are discussed for rotational transitions of ammonia and acetonitrile. These effects are caused by partially overlapped, but unresolved line profiles of individual hyperfine components.