High resolution emission spectra of H2 and D2 near 80 nm

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High resolution emission spectra of H2 and D2 near 80 nm

M. Larzillière, F. Launay, J.-Y. Roncin

To cite this version:

M. Larzillière, F. Launay, J.-Y. Roncin. High resolution emission spectra of H2 and D2 near 80

nm. Journal de Physique, 1980, 41 (12), pp.1431-1436. �10.1051/jphys:0198000410120143100�. �jpa-

00208968�

High resolution emission spectra ^of H2 ^{and D2 near 80 nm}

M. Larzillière (*), ^F. Launay (**) ^{and J.-Y. Roncin} (*)

(*) Equipe ^de Spectroscopie, ^C.N.R.S. (+), E.M.S.E., 158, Cours Fauriel, ⁴²⁰²³ Saint-Etienne Cedex, France (**) Observatoire de Paris, Departement d’Astrophysique Fondamentale,

G.R. 24 du C.N.R.S., ⁹²¹⁹⁰ Meudon, France (Reçu ^{le 13} juin 1980, accepté ^{le 22 août} 1980)

Résumé.

Quelques ^{raies ont} été observées dans le spectre d’émission ultraviolet lointain de l’hydrogène ^{et du}

deutérium. Ces raies sont attribuées à des transitions partant ^{de niveaux de l’état} 3p03C0D 103A0u- situés au-delà de la limite de dissociation

H(ls) ⁺ H(n

2) près ^{de 84,5}

et, pour certains, au-delà de la premiere ^{limite d’ioni-}

sation près ^de 80,4 nm, l’état ^{inférieur étant X} 1 03A3g+ (v" = 1). ^{Les résultats sont}

^accord

^{les mesures de taux}

de prédissociation ^{et de} préionisation. ^{La mesure} précise ^des positions ^{de raies} permet ^{de déduire des constantes} moléculaires

très bon accord

les calculs théoriques.

Abstract.

A few lines have been observed in the far ultraviolet emission spectrum of molecular hydrogen ^and deuterium. They ^are assigned ^to transitions from levels of the 3p03C0D 103A0 u- ^{state, lying above the} dissociation limit into H(ls) + H(n

2),

^{84.5 nm,} and, ^for

^of them, above the first ionization limit

80.4 _nm, the lower state being ^X 103A3g+ (v" = 1). This is in fair agreement with measured predissociation ^and preionization yields. ^{Accurate line} position measurements lead to molecular constants in very good agreement with theoretical calculations.

Classification Physics ^Abstracts 33.20N

1. Introduction. -’A few _{years ago} Roncin, ^Dama-

ny and Jungen gave ^a preliminary report [1] ^{about the} observation, ^at wavelengths shorter than 85 nm, of weak emission lines of H2 (D2) ^{which we} readily assigned ^to transitions from superexcited ^{levels, of}

the 3pnD lllü ^{state, lying} above the dissociation limit into H(ls) ⁺ H(n

2), ^{near 84.5 nm} and, ^for the higher ^ones, above the first ionization limit near

80.4 nm, the lower level being ^{the v"}

^{1 of the} ground

state X 1 E g+. These excited levels are known from the

absorption ^{data of Monfils} [2] and Takezawa [3].

Lines from such high energy levels are usually ^absent

in emission, ^{due to} preionization and/or predissocia-

tion [4]. ^If present, such short wavelength ^{lines are}

weak so that they ^are reabsorbed in classical discharges

whereas they ^show up in our spectra obtained in a low pressure windowless discharge. However, ^our spectra

were taken in the first order of the grating ^{so that} wavelength ^{standards were needed in a} region ^where

very few lines are measured with enough accuracy, i.e. to 0.000 01 nm. As a few more standards are now

available [5] ^{and as} the resolution of ^the spectrograph

has been increased, ^{we are in} position ^to give ^accurate

(’) L.A. 171, Universités de Saint-Etienne et Lyon ^1.

data and to derive molecular constants in fair _agree- ment with the ab initio calculation of Kolos and Rych-

lewski [6] and the multichannel quantum ^defect theory (M.Q.D.T.) ^of Jungen and Atabek [7]. ^Our

results _agree also with the recent fluorescence work of

Glass-Maujean, Breton and Guyon [8, 9, 10].

2. Experimental. - The presence of ^a magnetic

field of 0.1 tesla in the discharge lamp [11] ^makes possible ^{to run the source at} pressure ^as low as about 10- 2 torr, ^{so that} reabsorption ^{at short} wavelengths

can be avoided. Incidentally, because of the low flow rate, this technique ^also opens the possibility ^{of inves-} tigating expensive isotopic species. ^The lamp ^is operated ^{at 350 V-400 mA.}

The spectra ^{have been} photographed in the first order of the Meudon Observatory Eagle mounting

V.U.V. 10 metre concave grating spectrograph ^[12].

The instrument is now fitted with a concave

(R

^10.685 m), ^{3 600} lines/mm Jobin-Yvon inter- ference (holographic) grating ^which gives ^a plate ^factor

of 0.026 nm jmm ^{and a} resolving limit of 0.000 5 nm

(i.e. ^0.75 cm-1 at 80 nm) ^{with a} 15 pm slit width. The observed emission lines are quite ^{weak : on Kodak}

SWR plates ^the required exposure time is about

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:0198000410120143100

1432

4 hours, ^{i.e. 30 times} longer ^{than that} required ^{in the} wavelength region ^{near 100 nm.}

As already pointed ^{out the main} difficulty ^{lies in} wavelength calibration because of the sparsity ^of

standard lines in the far U.V. Reference lines are

obtained in two ways : Ar 1 by flowing argon in the low pressure discharge lamp ^itself operated ^{at 500 V-}

400 mA, ^{Cu II and 0 1} by flowing ^{helium in an auxi-} liary ^water cooled windowless hollow cathode dis-

charge lamp operated ^{at 600} V, ^{500 mA. The} émission

lines of H2 being ^far apart ^{in this} spectral range it is not

confusing ^to superimpose the reference lines to the

investigated spectrum ^{in order to} inçrease ^{the accu-}

racy. The plates ^{are measured on} the Meudon Obser- vatory photoelectric comparator [13] ^which gives ^an

accuracy of _{1 pm} on line position. ^The wavelength

accuracy is estimated to be + 0.0001 ^nm ( ± ^{0.15 cm -1}

near 80 nm).

3. Results and discussion.

Predissociation and

preionization ^{have been} definitely established in the

absorption spectrum of H2 by broadening, asymmetric

line shape ^and apparent emission of numerous R and P rotational lines, ^{but no} broadening of Q ^rotational

lines has ever been detected [14, 15, 16, 17].

Using ^the absorption data of Monfils [2] ^{and Take-}

zawa [3] ^{it is} easy ^to identify ^{the few} rotational lines of H2 ^and D2 ^{spectra showed on figures 1 and 2} respectively. All of the identified lines are Q(J) ^lines,

with J

1, 2, 3 ⁱⁿ H2 ^and 1, 2, 3, 4 ⁱⁿ D2, while R and P lines are entirely absent. The exponential ^decrease

of intensity, preventing observation of higher ^{J lines,}

is clearly ^modulated by intensity alternation typical ^of spin statistics in H2 ^and D2 [18]. The observed lines form the (v’, ^{v" -} 1) vibrational progression ^{of the} 3p7cD ’17: - ^X 1 Lg+ transition. As a matter of fact the state D 1 llu+ (upper ^{state of R and} P lines) predisso-

ciates through rotational interaction with the B’

’1+ ^state which dissociates into H(ls) ⁺ H(n

2).

This is not the case of D ’Ilu ^{(upper state of Q lines).}

The appearance of Q(J) ^{lines in our} spectra ^{is also in} accordance ^with recent measurements of predisso-

Fig. ^1. - Emission spectrum ^of H2

in the far ultraviolet. Refe-

rence

lines

from 0 I and Cu I1. AU the identified reference lines

are

marked at top ^{of the} spectra.

Table 1.

Measured wavelength ^À (nm) and derived wavenumber (J (cm -l) of ^the emission lines Q(J) forming ^the (v’, ^{v" =} 1) vibrational progression of ^the 3pnD lllu- - ^X 1 ’ transition in H2. ^{In the}

last column are listed the values of «a recalculated using

the graphical ^values of Bv.

ciation [8, 9] ^{and of} preionization yields [19], ^which

have been found negligible ^{for the} lines under conside- ration. Some weaker lines belonging ^{to the} (v’,

v" = 0,2) progressions ^{of the same} D-X transition have been detected but not measured.

No photograph ^is given ^of spectra taken with HD

as no line other _{than very} weak H2 ^and D2 lines could be detected whereas in the wavelength range longer

than 100 nm we have clearly recognized ^{known HD}

lines [20]. ^{It is not too} surprising ^that all excited levels

lying ^{above the} dissociation limit are predissociated

in HD, ^since this molecule is heteronuclear and therefore has lower symmetry ^than H2 ^and D2. ^The

asymmetry yields additional vibronic coupling ^effects

as has been demonstrated by Dabrowski and Herz-

berg [20] ^{for the} ground ^state.

Table II.

Same ^as table I for D2.

The measured wavelengths ^{and the} corresponding

wavenumbers are listed in tables 1 and II. Ground state energy level values of Stoïcheff [21] ^{allow us to}

derive the values E,(J) ^{of the D} 1 n u- state, referred ^to the bottom of the ground ^state potential energy ^curve.

They ^{are listed on table III.}

To a first approximation

Therefore, ^{for each value of v,} Ev ^is plotted ^versus J(J ⁺ 1). ^We verify ^{that we} get straight lines whose

slope Bv and ordinate Ev(O) ^{at J}

^{0 are determined} graphically. ^{In table IV our values} of BU ^are compared

to the ab initio values computed by ^{Kolos and} Rych-

lewski [6]. ^The agreement ^{is to within} + ^0.037 cm-’

for H2 ^{and 0.019 cm-1 for} D2. ^Previous comparison

with experimental ^results [2] gave discrepancies ^of

Table III.

Energy level values Ev(J) ^{in cm-’} of ^the

D ’Hù ^state, referred ^to the bottom of ^the ground ^state

potential energy ^curve.

1434

Table IV.

Comparison ^between graphical Ev values and ab initio Bv ^values [6].

0.36 cm-1 for H2 ^{and 0.28 cm -l for} D2 [6]. ^The experimental B,, ^{values cannot be} further refined because R and P branches are missing in emission.

As not enough ^{J values are} observed, ^{it has no} meaning

to introduce the next term Dv[J(J ⁺ 1)] 2 ^{in the deve-} lopment (3.1) ^of E,,(J). ^{However, we have} adopted D,

values of 0.015 cm-1 for H2 ^{and 0.005 cm- 1 for} D2 ⁱⁿ

order to minimize the systematic discrepancy ^between

our data and those of Kolos and Rychlewski. ^The

curve B(v) displayed ^on figure 3, ^is perfectly smooth, proving definitely ^{that the state} ’H ù ^{does not expe-}

rience _any perturbation that could arise from configu-

ration mixing.

Fig. ^3.

Rotational constant Ev (cm - 13)

function of

From the values of E,(O) ^we derived vibrational

spacings AG(v ⁺ 1/2), listed in table V, ^and compared

to ab initio values [6]. ^{The values} Ev(O) ^{are then used to}

Table V.

Comparison ^{between values} of AG(v ⁺ 1/2) (cm - l) ^obtained from graphical ^determi-

nation of Ev(O) ^to those obtained from ab initio calcu- lation [6].

compute, by ^{a least} square fit, ^{the five constants in} the

development

In turn, ^the derived constants are used to draw smooth values of Ev(0) ^{and of} OG(v ⁺ 1/2). ^These

values of AG are included in table V.

In tables VI and VII our experimental ^values Ev,(I)-E,,,(O) ^are compared ^{to the ones} computed by Jungen and Atabek using the multichannel quantum defect theory (M.Q.D.T.) [7]. Their values represent ^a fit of the quantum ^{defect curve} /131t(R) ^{to the levels}

observed by Takezawa. The present ^{agreement is to} within ± ^{0.50 cm -1 for} H2 and ± 0.42 cm -1 for D2.

Comparison ^to previous experimental ^data gave ^a

mean deviation of 0.54 cm -l and 0.39 cm -l respecti- vely, ^for H2 ^and D2. ^{It is} interesting ^{to note that our}

set of data gives slightly ^better agreement ^{where in} addition the scatter is now the same in H2 ^and D2. ^This

shows that the fitted quantum ^{defect curve of refe-}

rence [7] ^{must be} quite ^{accurate. It has to be} pointed

Table VI.

Comparison between the experimental ^values of Ev,(I)-Ev"(O) ^and the values calculated by ^the

multichannel quantum defect theory (M.Q.D.T.) [7]lor H2. ^The comparison between previous experimental ^values [4] ^and M.Q.D.T. ^{is recalled.}

Table VII.

Same as table VI for D2.

out that the value v’

12 is excluded from the calcu- lation of the mean deviation in the case of H2 ^{as the} M.Q.D.T. calculation was not completely ^{refined at} large R ^values [22].

Table VIII.

Molecular constants (in cm -l) of ^the

state 3pnD lllu- ^of H2 ^and D2.

Finally ^our Bv ^{values are} put ^{into the} development

A least square fit gives the nine molecular constants that are listed in table VIII. Previous values of the literature are tabulated in [23].

4. Concluding ^remarks.

^{From a limited amount}

of experimental ^{data we} have been able to derive molecular constants giving ^fair agreement ^{with theo-} retical calculations. The next step will consist in mea-

suring emission spectra of H2, ^{HD and} D2 ^{in the region}

between 85 and 105 nm where no precise measurement has ever been reported. The work is under way ^at Meudon Observatory.

Acknowledgments.

The authors wish to thank Dr. V. Kaufman (N.B.S., Washington, D.C.), ^for

advices in design of the hollow cathode, ^{Dr. Ch. Jun-}

gen (Orsay) for critical reading ^{of the} manuscript ^and

Mr. M. Benharrous for assistance in the experimental

work.

94

1436

References

[1] RONCIN, J.-Y., DAMANY, H., JUNGEN, Ch.,

^{V. U. V. Radiation} Physics », ^Edited by ^{E. E.} Koch, R. Haensel and C. Kunz

(Pergamon-Vieweg, Braunschweig) ^{1974, p. 52.}

[2] MONFILS, A., J. Mol. Spectrosc. ¹⁵ (1965) 265 and 25 (1968)

513.

[3] TAKEZAWA, S., ^{J. Chem.} Phys. ⁵² (1970) ^{2575 and} private

communication cited in [7].

[4] HERZBERG, G., Spectra of Diatomic ^Molecules (Van ^Nostrand, Princeton) ^1950.

[5] KAUFMAN, V., EDLEN, B., ^J. Phys. ^Chem. Ref. ^{Data 3} (1974)

825.

[6] KOLOS, W., RYCHLEWSKI, J., ^{J. Mol.} Spectrosc. ⁶² (1976) ^109.

[7] JUNGEN, Ch., ATABEK, O., ^{J. Chem.} Phys. ⁶⁶ (1977) ^5584.

[8] GLASS-MAUJEAN, M., BRETON, J., GUYON, P.-M., Chem. Phys.

Lett. 63 (1979) ^591.

[9] GUYON, P.-M., BRETON, J., GLASS-MAUJEAN, M., ^Chem. Phys.

Lett. 68 (1979) ^314.

[10] BRETON, J., GUYON, P.-M., GLASS-MAUJEAN, M., Phys. ^Rev.

A. 21 (1980) 1909.

[11] ANVAR, Contract Nb. 7296800, Instrument S.A. France.

[12] LAUNAY, F., ^Le Courrier du C.N.R.S. 12 (1974) ^10.

[13] LAUNAY, F., «Proceedings of the International Conference

Image Processing Techniques ⁱⁿ Astronomy », ^Utrecht,

March 1975 (Reidel, Dordrecht, Holland) ^1975.

[14] NAMIOKA, T., ^{J. Chem.} Phys. ⁴¹ (1964) ^2141.

[15] COMES, ^F. J., SCHUMPE, G., Z. Naturforsch. ^26a (1971) ^538.

[16] HERZBERG, G.,

Topics ^{in Modern} Physics. ^{A tribute to E. U.}

Condon » (Colorado Univ. Press) 1971, p. 191.

[17] HERZBERG, G., JUNGEN, Ch., ^{J. Mol.} Spectrosc. ⁴¹ (1972) ^425.

[18] ^Ref. [4], p. 207 and 134.

[19] DEHMER, P. M., CHUPKA, ^W. A., ^{J. Chem.} Phys. ⁶⁵ (1976) ^2243.

[20] DABROWSKI, I., HERZBERG, G., ^{Can. J.} Phys. ⁵⁴ (1976) ^525.

[21] STOICHEFF, ^B. P., Can. J. Phys. ³⁵ (1957) ^730.

[22] ^Ref. [7] p. 5594 and Fig. ^6.

[23] HUBER, K. P., HERZBERG, G.,

^Constants of Diatomic Mole-

cules » (Van Nostrand Reinhold Co.) ^1979.