vibrational partition function based on low-resolution IR measurements by
J. L. Duncan et al., J. Mol. Spectrosc. 69 (1978) 123;
doi:10.1016/0022-2852(78)90033-4.

Measured fundamentals up to 2800 cm-1:
nu2:  2240.30
nu6:  1447.85
nu3: ~1390
nu7:  1040.68
nu4:   911.21
nu8:   362.10

500: 3.0030
300: 1.5175
225: 1.2383
180: 1.1219
150: 1.0653
120: 1.0266
100: 1.0110
 75: 1.0019