Nuclear Magnetic Hyperfine Spectra of H35Cl and H37Cl

The nuclear hyperfine spectra of H³⁵Cl and H³⁷Cl have been studied in the limit of zero external magnetic field by a molecular‐beam magnetic resonance spectrometer. Thirteen lines of the H³⁵Cl spectrum were observed in the range 20–230 kHz, and eight lines of the H³⁷Cl spectrum were observed in the range 20–140 kHz. The spectra were analyzed by a zero‐field magnetic hyperfine Hamiltonian. For each molecule the proton spin–rotation constant $c_p$ and the total tensor spin–spin constant $d$ have been measured, and an upper limit for the magnitude of the scalar part of the electron‐coupled spin–spin constant $\mathrm{|\hspace{0.17em}\delta \hspace{0.17em}|}$ has been established. The calculated transition frequencies agree with the observed spectra and the independent determinations of the constants for the two molecules are consistent with the first‐order theory of isotopic effects. The measured constants for H³⁵Cl are $c_p\text{\hspace{0.17em}=\hspace{0.17em}+41.70\hspace{0.17em}±\hspace{0.17em}0.10}\mathrm{kHz}$ and $\text{d\hspace{0.17em}=\hspace{0.17em}+2.20\hspace{0.17em}±\hspace{0.17em}0.04}\mathrm{kHz}$ ; for H³⁷Cl they are $c_p\text{\hspace{0.17em}=\hspace{0.17em}+41.66\hspace{0.17em}±\hspace{0.17em}0.10}\mathrm{kHz}$ and $\text{d\hspace{0.17em}=\hspace{0.17em}+1.86\hspace{0.17em}±\hspace{0.17em}0.04}\mathrm{kHz}$ . The upper limits for $\mathrm{|\hspace{0.17em}\delta \hspace{0.17em}|}$ in H³⁵Cl and H³⁷Cl are 0.33 and 0.27 kHz, respectively.