\\ Species Tag:        &    1001 & Name:&  H-atom        
\\ Version:            &       1 & &$^2$S$_{1/2}$ ground state
\\ Date:       &  Oct. 1979     & &
\\ Contributor:&  H. M. Pickett & &
\\             &                 & &
\\ Lines Listed:       &       1 & Q(300.0)=&        4.000
\\ Freq. (GHz) $<$     &       2 & Q(225.0)=&        4.000
\\ Max. J:             &       1 & Q(150.0)=&        4.000
\\ LOGSTR0=            &    -9.1 & Q(75.00)=&        4.000
\\ LOGSTR1=            &         & Q(37.50)=&        4.000
\\ Isotope Corr.:      &     0.0 & Q(18.75)=&        4.000
\\ Egy. (cm$^{-1}$) $>$& 0.0479  & Q(9.375)=&        4.000
\\ $\mu_a$ = &                   & A=&
\\ $\mu_b$ = &                   & B=&
\\ $\mu_c$ = &                   & C=&
\headend

The atomic hydrogen line at 21 cm has been measured to a precision of 0.001 
Hz (L. Essen, R. W. Donaldson, M. J. Bangham, and E. G. Hope, 1971, Nature
{\bf 229}, 110). The average spontaneous emission lifetime of the 
three F = 1 states is $2.876 \times 10^{-15}$ sec$^{-1}$.