SIMBAD references

The molecular structure of methyl formate is determined from ab initio calculations. The molecule presents two conformers (cis and trans) with a 5.3 kcal/mol difference in energy. In the most stable cis conformer, the carbonyl group eclipses the methyl group. The internal rotation barriers are V₃(cis)=368/cm and V₃(trans)=26/cm for the methyl group and V^CO=4826/cm for the CO group. The dependence of the spectroscopic parameters on the torsional motions is detailed. The rotational-torsional energy levels have been calculated variationally up to J=6 using a flexible model depending on the two torsional modes. Far-infrared frequencies and intensities are determined at room temperature. The rotational parameters have been computed to be A=20,040.473 MHz, B=6974.140 MHz, C=5350.705 MHz, D_J=-0.510 kHz, D_JK=1.566 kHz, and D_K=-0.619 kHz; and A=20,040.492 MHz, B=6974.399 MHz, C=5350.851 MHz, D_J=2.070 kHz, D_JK=14.712 kHz, and D_K=5.898 kHz at the symmetric and E components of the cis ground state, respectively. The corresponding values for trans-methyl formate are A=47,380.066 MHz, B=4738.781 MHz, and C=4430.339 MHz; and A=47,389.697 MHz, B=4737.751 MHz, and C=4429.607 MHz.