Dipole Moment and Hyperfine Parameters of H35Cl and D35Cl

The molecular‐beam electric resonance spectra of H ³⁵Cl and D ³⁵Cl have been analyzed. The molecular constants obtained in the observed states are as follows (numbers in parentheses are the errors in the final significant figures): $$\begin{array}{ccccc}& & \mathrm{H}{}^{35}\mathrm{Cl}& & \\ & \text{υ\hspace{0.17em}=\hspace{0.17em}0, J\hspace{0.17em}=\hspace{0.17em}1}& \text{υ\hspace{0.17em}=\hspace{0.17em}0, J\hspace{0.17em}=\hspace{0.17em}2}& \text{υ\hspace{0.17em}=\hspace{0.17em}1, J\hspace{0.17em}=\hspace{0.17em}1}& \text{υ\hspace{0.17em}=\hspace{0.17em}2, J\hspace{0.17em}=\hspace{0.17em}1}\\ {\mathrm{eqQ}}_{\mathrm{Cl}}(\mathrm{kHz})& \text{−\hspace{0.17em}67 618.93(47)}& \text{−\hspace{0.17em}67 638.53(15)}& \text{−\hspace{0.17em}69 272.89(93)}& \text{−\hspace{0.17em}70 908.1(24)}\\ C_H(\mathrm{kHz})& \text{−\hspace{0.17em}41.80(25)}& \text{−\hspace{0.17em}41.68(4)}& \text{−\hspace{0.17em}41.09(24)}& \text{−\hspace{0.17em}39.94(94)}\\ C_{\mathrm{Cl}}(\mathrm{kHz})& \text{+\hspace{0.17em}53.851(42)}& \text{+\hspace{0.17em}53.887(14)}& \text{+\hspace{0.17em}58.597(45)}& \text{+\hspace{0.17em}63.68(17)}\\ \mathrm{\mu (}\mathrm{D})& \text{1.1085(5)}& \text{1.1085(5)}& \text{1.1390(10)}& \text{1.1685(10)}\\ & & \mathrm{D}{}^{35}\mathrm{Cl}& & \\ & \text{υ\hspace{0.17em}=\hspace{0.17em}0, J\hspace{0.17em}=\hspace{0.17em}1}& \text{υ\hspace{0.17em}=\hspace{0.17em}0, J\hspace{0.17em}=\hspace{0.17em}2}& \text{υ\hspace{0.17em}=\hspace{0.17em}0, J\hspace{0.17em}=\hspace{0.17em}3}& \text{υ\hspace{0.17em}=\hspace{0.17em}1, J\hspace{0.17em}=\hspace{0.17em}1}\\ {\mathrm{eqQ}}_D(\mathrm{kHz})& \text{+\hspace{0.17em}187.36(30)}& \text{+\hspace{0.17em}187.0(28)}& & \text{+\hspace{0.17em}184.8(38)}\\ {\mathrm{eqQ}}_{\mathrm{Cl}}(\mathrm{kHz})& \text{−\hspace{0.17em}67 393.38(9)}& \text{−\hspace{0.17em}67 403.32(29)}& \text{−\hspace{0.17em}67 418.00(10)}& \text{−\hspace{0.17em}68 583.1(10)}\\ C_D(\mathrm{kHz})& \text{−\hspace{0.17em}3.295(46)}& \text{−\hspace{0.17em}3.308(80)}& & \\ C_{\mathrm{Cl}}(\mathrm{kHz})& \text{+\hspace{0.17em}27.426(7)}& \text{+\hspace{0.17em}27.430(28)}& & \text{+\hspace{0.17em}29.121(62)}\\ \mathrm{\mu (}\mathrm{D})& \text{1.1033(5)}& \text{1.1033(5)}& & \text{1.1256(10)}\end{array}$$ The above dipole moments were used in conjunction with available absolute infrared intensity measurements of vibrational bands to obtain the dipole moment function of the molecule. The derivatives with respect to the internuclear distance $R$ , evaluated at $R_e$ , for H ³⁵Cl are: ${\mathrm{(d\mu \hspace{0.17em}/\hspace{0.17em}dR)}}_e\text{\hspace{0.17em}=\hspace{0.17em}+\hspace{0.17em}0.925\hspace{0.17em}±\hspace{0.17em}0.020}\mathrm{D}{\mathrm{/\AA ;\; (d}}^2{\mathrm{\mu \hspace{0.17em}/\hspace{0.17em}dR}}^2{)}_e\text{\hspace{0.17em}=\hspace{0.17em}+\hspace{0.17em}0.16\hspace{0.17em}±\hspace{0.17em}0.11}\mathrm{D}{\mathrm{/\AA }}^2{\mathrm{;\; (d}}^3{\mathrm{\mu \hspace{0.17em}/\hspace{0.17em}dR}}^3{)}_e\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}3.83\hspace{0.17em}±\hspace{0.17em}0.90}\mathrm{D}{\mathrm{/\AA }}^3{\mathrm{;\; (d}}^4{\mathrm{\mu \hspace{0.17em}/\hspace{0.17em}dR}}^4{)}_e{\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}9.3\hspace{0.17em}±\hspace{0.17em}4.5 D/Å}}^4$ . In addition, an isotope effect in the dipole moment due to a violation of the Born–Oppenheimer approximation was observed by comparing the relative HCl and DCl dipole moments. The distance derivatives of the field gradient, $q_{\mathrm{Cl}}$ , at the ³⁵Cl nucleus were also determined: