Pure Rotational Spectrum and Electric Dipole Moment of CH3D

摘要

The pure rotational spectrum of CH3D in the ground vibrational and electronic state has been observed using a farhyphen;infrared grating spectrometer. This spectrum is of particular interest because the electric dipole momentmgr;arises entirely from an isotopic substitution. Ten distinct lines have been observed in the frequency range from 40 to 120 cmminus;1, and have been identified with thelpar;Jthinsp;rarr;thinsp;Jthinsp;plus;thinsp;1rpar;transitions for the rotational levelsJthinsp;equals;thinsp;5thinsp;minus;thinsp;14. For the (6thinsp;rarr;thinsp;7) line, the absolute intensity and the linewidth were determined by a curve of growth method. It was found that, for this line, the dipole momentmgr;thinsp;equals;thinsp;lpar;5.68thinsp;plusmn;thinsp;0.30rpar;thinsp;times;thinsp;10minus;3Dand the broadening parameterggr;0thinsp;equals;thinsp;lpar;0.075thinsp;plusmn;thinsp;0.012rpar;cmminus;1sol;amagat. This measurement constitutes the first correct experimental determination of the dipole moment of CH3D. By making further intensity measurements on other lines, it was shown that, to within 6percnt;,mgr;is independent ofJin the range5thinsp;le;thinsp;Jthinsp;le;thinsp;12. A detailed account of the experimental methods used to make the intensity measurements is given. It was also determined that the rotational constantB0thinsp;equals;thinsp;lpar;3.882thinsp;plusmn;thinsp;0.002rpar;cmminus;1and the distortion constantDjthinsp;equals;thinsp;lpar;7.7thinsp;plusmn;thinsp;0.3rpar;thinsp;times;thinsp;10minus;5cmminus;1.