Vinyl isocyanate, C2H3NCO, consists of two conformers, trans and cis; 
the latter is about 301 cm-1 higher in energy, see Vávra et al..

              v = 0, both    v = 0, trans        v = 0, cis
TEMPERATURE - Q(SPIN-ROT.)  - Q(SPIN-ROT.)   - Q(SPIN-ROT.)
    300.000   62500.3370      46450.5158        16049.8212              
    225.000   36581.6764      30146.5885         6435.0879              
    150.000   17733.8930      16397.8411         1336.0519              
     75.000    5820.7144       5794.4284           26.2860              
     37.500    2048.9122       2048.8833            0.0289              
     18.750     724.9791        724.9791            0.0000              
      9.375     256.8095        256.8095            0.0000              
      5.000     100.3733        100.3733            0.0000              
      2.725      40.6496         40.6496            0.0000     

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Vibrational contributions to the partition function of trans vinyl isocyanate

Vibrational correction factors are taken from (1):

TEMPERATURE       F_vib   
    300.000       9.03 
    225.000       4.89 
    150.000       2.65 
     75.000       1.39 
     37.500       1.06 
     18.750       1.00 
      9.375       1.00 
      5.000       1.00
      2.725       1.00

Their values were estimated from quantum-chemical calculations using 
anharmonic frequencies of the eighteen normal vibrational modes which are:

Mode / Freq.(cm-1)
 1     3149.9
 2     3079.0
 3     3051.5
 4     2301.7
 5     1635.6
 6     1490.3
 7     1408.3
 8     1328.3
 9     1109.3
10      853.5
11      656.0
12      453.1
13      136.5
14      972.1
15      915.6
16      698.4
17      601.1
18       78.3

The experimental values for the two lowest vibratinal modes are available from 
microwave relative intensity measurements in (2). While there is an
agreement between the literature value and calculated value for 
nu_18 mode, a discrepancy is found for nu_13 mode. Details are discussed in 
Vávra et al..