A two-step excitation experiment has been employed to measure the collisional rate coefficients and to study the velocity distribution of Cs͑6P 1/2 ͒ atoms that have undergone a single hyperfine state-changing collision with Ar. In addition, argon pressure broadening rates and shifts of the cesium 6P 1/2 ͑FЈ͒ → 8S 1/2 ͑FЉ͒ transitions have been determined. In the experiment, a single mode, cw Ti:sapphire laser is tuned to line center of the 6S 1/2 ͑F =4͒ → 6P 1/2 ͑FЈ = 3 or 4͒ transition. Then, the frequency of a single mode cw dye laser is scanned over the 6P 1/2 → 8S 1/2 manifold to probe the populations of the 6P 1/2 hyperfine levels. Absorption of probe laser photons is monitored by detecting 8S 1/2 → 6P 3/2 fluorescence. The experiment is conducted at room temperature, where the Cs density is low ͑n ϳ 3.4ϫ 10 10 atoms cm −3 ͒, and thus the probability of a Cs-Cs collision is negligible during the Cs͑6P 1/2 ͒ radiative lifetime. The Ar pressure is varied from 0 to 1.52 Torr, and Cs-Ar collisions cause population to be transferred from the directly excited 6P 1/2 ͑FЈ͒ level to the other 6P 1/2 hyperfine level. The data are analyzed using a density matrix formalism to yield the rate coefficients for Cs͑6P 1/2 ͒-Ar hyperfine state-changing collisions. In addition, the one-dimensional velocity changing collision kernel for Cs͑6P 1/2 ͒ atoms prepared with v z = 0 that undergo FЈ =3↔ FЈ = 4 hyperfine state-changing collisions with argon is reported.