Raman spectra of gases. XVIII.thinsp; Internal rotational motions in ethylamine and ethylaminehyphen;d2

摘要

The Raman spectra of gaseous CH3CH2NH2and CH3CH2ND2have been recorded from 100 to 600 cmminus;1. Both ground and excited states of the methyl and amino torsional modes for thegaucheconformer have been observed. The overtone of the methyl torsion has also been observed for thegaucheconformer. The methyl barriers in thegaucheconformers of the CH3CH2NH2and CH3CH2ND2molecules were found to be 3.71plusmn;0.05 and 3.59plusmn;0.05 kcal/mole, respectively. The apparent difference in the barrier heights for these two isotopic species is attributed to a difference in the coupling between the methyl and amino torsions in these two molecules. The potential function for internal rotation around the Cndash;N bond in CH3CH2ND2was determined and the following potential constants found:V1=279plusmn;16 cmminus;1,V3=707plusmn;4 cmminus;1,V6=minus;12plusmn;3 cmminus;1. The energy difference between the potential energy minima of thegaucheandtransconformations is 207 cmminus;1(0.592 kcal/mole) with thetransbeing the more stable. The calculatedgauchendash;gauchebarrier is 779 cmminus;1(2.23 kcal/mole) and thetransndash;gauchebarrier is 572 cmminus;1(1.64 kcal/mole). A similar potential function was determined for the CH3CH2NH2isomer but the fit to this onehyphen;dimensional model was not as good as that obtained for the deuterium compound probably because of the greater coupling in the light molecule.