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.

Estimated fundamentals up to 2200 cm-1:
nu6:  1446.77
nu3: ~1380
nu7:  1032.38
nu4:   894.67
nu8:   361.64

300: 1.5215
225: 1.2395
180: 1.1225
150: 1.0656
120: 1.0267
100: 1.0111
 75: 1.0019