Refined molecular constants for the Ill; states of H2

MICHEL LARZILLI~RE' De'parternent de physique, Laboratoire de physique atomique et mole'culaire et Centre de recherche sur les atomes et

les mole'cules, Faculte' des sciences et de ge'nie, Universite' Laval, Que'bec (Que'.), Canada GIK 7P4

F R A N ~ I S E LAUNAY Observatoire de Paris, De'parternent d'astrophysique fondamentale, (Unite' associe'e 812) ,

92195 Meudorl Principal Ce'dex, France

AND

JEAN-YVES RONCIN ~ q u i ~ ? de spectroscopic, Centre, national de la recherche scientzj5que (CNRS) , (Unite' associe'e 1 7 1 ) ~ ,

Ecole des rnines de Saint-Etienne, 158, Cours Fauriel, 42023 Saint-Etienne Ce'dex, France

Received August 8 , 1985

Refined molecular constants for the states C , D , D ' , and D" In; of Hz have been obtained using the best values of the ground-state constants derived recently by Dabrowski. A few high J values of C and D states are reassigned.

Les constantes moltculaires des ttats C , D , D' et D" In; de HZ sont amCliorCes en prenant pour constantes de 1'Ctat fondamental les valeurs obtenues rCcemment par Dabrowski. Quelques valeurs ClevCes de J des Ctats C et D sont riattributes.

Can. 1. Phys. 63, 1416 (1985)

1. Introduction Until recently, the vacuum ultraviolet emission spectrum of

H2 was known in the Schumann region, down to 118 nm only, from the work of Herzberg and Howe (1). Extension to shorter wavelengths has appeared very recently down to 100 nm in the work of Dabrowski concerned with the band systems B '1: - X ICgf and C 'nu+ X lCl(2) and down to 78 nm in the work of Roncin et al. concerned with the band systems C, D, D', and D" In; + x lc; (3).

It has to be pointed out first that, for the bands of the C In; - X system common to both measurements, the values of line positions agree remarkably well between each other, mostly within k 0 . 1 cm-l. Owing to the use of a low-pressure discharge lamp, reducing self-absorption, the bands terminating in u = 0 of the ground state show up in our spectrum. On the other hand, the use of a flash discharge allowed Dabrowski to get rotational lines up to J = 30 for the Lyman band system B IC: + X ' E l , which is not overlapped by any other band system at long wavelengths. Therefore, she was able to derive a more extended set of molecular constants for the ground state.

2. Discussion In the spectral region between 84.5 and 118 nm where the

spectrum is most congested, we were unable to ascribe unambiguously high Q(J) lines. When taking the new values of the ground-state constants, some of our lines with J r 7 were rejected from the fit and new assignments were made up to J = 14 for some bands. In Table 1, the new positions of the few reassigned lines are collected. Newly identified lines will be listed in an atlas that is in preparation.

'On leave from the Laboratoire de spectromttrie ionique et molC- culaire (associC au CNRS, Unite associCe 171), UniversitC de Lyon I , 43, boulevard du 11 novembre 1918, 69622 Villeurbanne CCdex, France.

2Laboratoire associC au CNRS, Universitt de Lyon I et Saint- ~ t i e n n e .

TABLE 1. Reassignment of some lines of the C In; + and D In; + X transitions

"For the lines D-X 0-0 Q10,O-1 Q10, 1-1 Q8, and 1-6 Q8 no value can be retained.

bBlended lines.

In view of the good agreement between our measurements and those of Dabrowski, we decided to fit simultaneously both sets of values relating to the band system C In; -, X '1:. Then 737 lines were fitted with a standard deviation of 0.41 cm-'. The resulting constants for the state C In; are given in Table 2. They fall quite close to those of Dabrowski and a somewhat smoother decrease of B,, D,, and H, is observed.

A new fit for the band system D In; + X 'C; leads to about the same number of rejected lines with J r 8. The same process applied to the band systems D' and D" 'n; + X IC; does not put any assignment into question. Most of the lines of these systems lie in a spectral range in which assignments are less ambiguous as the spectrum is much less crowded owing to predissociation and (or) preionization of most of the excited levels. Tables 3 and 4 give molecular constants for the state D In; and the states D' and D" In; respectively.

We have verified that, for the C and D states, the agreement between the experimental values of AG(u + 112) and the ab initio values (4) is quite improved. The decrease of B, and D, values is only slightly smoother than before for all states.

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TABLE 2. Vibrational energy above u = 0, J = 0 of the X IC,+ state and rotational constants of the C In; state of Hz

u TU BU DC H , ( X lo5) Highest J used in fit

"Values from Dabrowski (2).

TABLE 3. Vibrational energy above u = 0, J = 0 of the X 'EL state and rotational constants of the D state of Hz

u T L BL D, Highest J used in fit

Acknowledgement We are grateful to UniversitC Lava1 for supporting the trip and

the stay of one ofus (J.-Y.R.) during three months in mid-1985.

TABLE 4. Vibrational energy above u = 0 , J = 0 of the X ' E i state and rotational constants of the D ' and D" In; states of Hz

u T O BU D, Highest J used in fit

"Constrained.

1. G. HERZBERG and L. L. HOWE. Can. J . Phys. 37, 636 (1959). 2. I. DABROWSKI. Can. J . Phys. 62, 1639 (1984). 3. J.-Y. RONCIN, F. LAUNAY, and M. LARZILLI~RE. Can. J . Phys.

62, 1686 (1984). 4 . W. K o ~ o s and J . RYCHLEWSKI. J . Mol. Spectrosc. 62, 109

(1976).

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