Notes. The partition function is calculated using the method described in Carvajal et al. (2019). The experimental vibrational energies are taken from Jones et al. (1976), and the torsional band ν₁₇ (CO-torsion) is calculated with CCSD(T) by Senent et al. (2014). The nuclear spin degeneracy is assumed as 1. ^(a) Classical rotational partition function, calculated for the A-species (the same value is expected for the E-species within this approximation) using rotational constants from Jones et al. (1976). ^(b) The torsional partition function, calculated using v_t = 0, 1, and 2. ^(c)The vibrational partition function, calculated using all the fundamental energy levels except the CH₃ torsional mode. ^(d)The rotation-torsion-vibration partition function.