  This paper studies irreducible characters of the $q$-rook monoid algebra
$R_n(q)$ using the vertex algebraic method. Based on the Frobenius formula for
$R_n(q)$, a new iterative character formula is derived with the help of the
vertex operator realization of the Schur symmetric function. The same idea also
leads to a simple proof of the Murnaghan-Nakayama rule for $R_n(q)$. We also
introduce the bitrace for the $q$-monoid and obtain a general combinatorial
formula for the bitrace, which generalizes the counterpart for the
Iwahori-Hecke algebra. The character table of $R_n(q)$ with $|\mu|=5$ is listed
in the appendix.
