  We reported a detailed experimental study of the cold collision of Barium
monofluoride (BaF) with buffer gas and the high-resolution spectroscopy
relevant with direct laser cooling. BaF molecules are efficiently produced with
laser ablation and buffer-gas cooled in a cryogenic apparatus. The laser
cooling relevant transition $|X^2\Sigma, v=0, N=1\rangle$ to $|A^2\Pi, v'=0,
J'=1/2\rangle$ is identified. The collision cross section with buffer gas is
measured to be $1.4(7)\times10^{-14} cm^{-2}$, which is very suitable for
buffer gas cooling. Both rotational and vibrational temperatures are
effectively cooled, and large mount of molecules are quenched into the desired
states. Our study provides an important benchmark for further laser cooling of
BaF molecule.
