A gaseous xenon fluoride contains one xenon atom per molecule. When an empty glass bulb is filled with a pure sample of the compound, the pressure inside the bulb is 18 torr. Hydrogen gas is added to the bulb until the total gas pressure reaches 72 torr. An electric spark causes the gases to react, converting all of the xenon fluoride to xenon and hydrogen fluoride. After the hydrogen fluoride is removed by reaction with solid potassium hydroxide, the final pressure of the xenon and unreacted hydrogen is 36 torr. What is the empirical formula of the xenon fluoride in the original sample?