Knowledge Bank

Previous $workers1,2$ observed in electric discharge a resonance spectrum in iodine vapour in the ultraviolet region. $One2$ of them has given the analysis of the spectrum photographed in the region 2360--2050 A with Hilger E1 spectrograph. Present author also repeated the experiment in India using Hilger E1 spectrograph. Preliminary analysis showed that the analysis of this spectrum could be improved and better constants for the ground state could be determined if the spectrum was photographed with high resolving instrument up to exciting line. Therefore this resonance spectrum has been photographed in the region 2370--1800 A with a 21-ft vacuum grating spectrograph in the second and third orders using a grating having 30,000 lines/inch. The spectrum was excited by microwave frequency which was found suitable to given high intensity. The analysis shows five doublet series excited by the resonance line 1830.4 A of iodine atom, extending from $v\prime =0$ up to nearly the dissociation limit of the ground state of $I2$ molecule. The rotational levels excited in the upper state are $v\prime =n,J=22$ and 25; $v\prime =n+1$, $J=49$ and 46, and $v\prime =n+5,J=87$ for five different series. The rotational constants for the ground state are given by the following two equations.\begin{eqnarray} B_{\nu}=0.0373405-0.00012079(v+1/2)+4.444\times 10^{-6}(v+1/2)^2\nonumber\ -1.839\times 10^{-3}-0.57\times 10^{-11}(v+1/2)^4\ D_{\nu}=1.99\times 10^{-9}+12.36\times 10^{-11}(v+1/2)\end{eqnarray} These constants probably are more reliable than those of Rank and Baldwin$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ as their calculations are limited to data known only up to $v\prime =20$ and hence they could see the effect of only first to constants, whereas in the present work data are known $v\prime =0$ up to $v\prime =82$. The constants for the upper state could be calculated as $Bn\prime =0.012427cm-1,\omega n=42.95cm-1$ where $n$, is the unknown vibrational quantum number in the upper state. The determination of the vibrational constants for the ground state is in progress which is expected to yield more higher order terms in the formula for the positions of the vibrational levels and perhaps to improve the constants already known.