Hence, λ λ t h = h 2 π π m k B T , where h is the Planck constant, m is the mass of a gas particle, k B is the Boltzmann constant, and T is the temperature of the gas. This can also be expressed using the reduced Planck constant ℏ ℏ = h 2 π π as λ λ t h = 2 π π ℏ ℏ 2 m k B T .