Forbidden Band Systems in Nitrogen. II. Theaprime;1Sgr;uminus;larr;X1Sgr;gplus;System in Absorption

摘要

Four bands of theaprime;1Sgr;uminus;larr;X1Sgr;gplus;system in nitrogen have been observed in absorption at high resolution in a path of 3.4 meteratmospheres, at 1444 A (1ndash;0), 1414 A (2ndash;0), 1358 A (4ndash;0), and 1331 A (5ndash;0). They consist ofQbranches only (Dgr;J=0). The observation of these bands, highly forbidden by the usual selection rules, is explainable by perturbations with the nearest1IIustates lying between about 98 000 cmmdash;1and 109 000 cmmdash;1above the ground state.The rotational analysis of each of the bands resulted in rotational constants and vibrational intervals foraprime;1Sgr;umdash;which agree very well with those obtained from the emission systemx1Sgr;gminus;rarr;aprime;1Sgr;uminus;. The electronic energy (T00) of stateaprime;1Sgr;umdash;is now precisely located at 67738.18 cmmdash;1(8.398 ev); this value combined with other data gives also the following electronic energies (T00):w1Dgr;u, 71697.68 cmmdash;1(8.889 ev);x1Sgr;gmdash;, 113210.98 cmmdash;1(14.036 ev); andy1IIg, 114165.18 cmmdash;1(14.154 ev).T00ofaprime;1Sgr;umdash;is close to that ofa1IIg: 68951.21 cmmdash;1(8.548 ev).The new energy fory1IIgis 0.339 ev lower than the minimum value deemed possible by Lofthus and Mulliken on the basis of an observed predissociation atv=0,J=10 of statey. That predissociation is now reinterpreted as most probably an accidental one resulting in the formation of2P+4S atoms instead of2D+2D atoms as formerly assumed.The intensity distribution in theaprime;1Sgr;uminus;larr;X1Sgr;gplus;system is found to be approximately proportional toJ(J+1)(2J+1) expmdash;B0Prime;J(J+1)hc/kT, whereB0Prime;=1.9898 cmmdash;1andT=300deg;K, in agreement with theory.From appearance pressures of the five forbidden systems of nitrogen now known in absorption, it is possible to estimate the transition probabilities. From these, together with a recent molecular beam determination of the mean lifetime of the statea1IIg, it is possible to estimate the lifetimes of the metastable states:A3Sgr;u+, 2.6times;10mdash;2sec,aprime;1Sgr;umdash;, 4.0times;10mdash;2sec. By comparison of the transition probability of the atmospheric oxygen bandslpar;b1Sgr;gplus;larr;X3Sgr;uminus;rpar;with that of the Vegardhyphen;Kaplan bands of nitrogenlpar;A3Sgr;uplus;larr;X1Sgr;gplus;rpar;, together with the known lifetime ofb1Sgr;g+, the value 6.5times;10mdash;3sec is found for the lifetime ofA3Sgr;u+, in fair agreement with the value given above.