Extension of Submillimeter Wave Spectroscopy below a Half-Millimeter Wavelength

Abstract

The methods of high-resolution microwave spectroscopy have been extended to $\lambda =0.43\mathrm{}$ mm. The J=5→6 rotational line of ${\mathrm{C}}^{12}$ ${\mathrm{O}}^{16}$ has been measured to be 691 472.60±0.60 Mc/sec. With other measured lower frequency transitions, this value leads to a centrifugal stretching constant $D_0=0.18390\mathrm{}\pm 0.00014$ Mc/sec and to $B_0=57\mathrm{}635.970\pm 0.003$ Mc/sec for ${\mathrm{C}}^{12}$ ${\mathrm{O}}^{16}$. Measurements of the three hyperfine components of the $J=0\mathrm{}\to 1$ transition of H${\mathrm{Cl}}^{35}$ at $\lambda =0.48\mathrm{}$ mm yield for this molecule ${\nu }_0=625\mathrm{}919.24\pm 0.52$ Mc/sec and $B_0=312\mathrm{}991.30\pm 0.26$ Mc/sec. With the infrared value of $B_0$ in wavelength units measured with great accuracy by Rank and his associates, our $B_0$ value yields the spectral value $c=299\mathrm{}792.8\pm 0.4 \mathrm{km}/sec$ for the velocity of light. This value is in agreement with, and is of comparable accuracy to, the best values obtained by other more direct methods for the measurement of $c$.