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Absorption spectrum of the xenon molecule in the vacuum ultraviolet region
Volume
13,
number 2
&EMICAL
15 February 197i “
PHYSICS‘ LETTERS : :
‘....
ABSORPTION SPEkTRUM OF THE.XENON MOLECULE IX THE VACUUM UL?kbIdLET REGIONM.-C. CASTEX 2ind N. SAMANY Lubom~oire desHautes Pressions, C.N.R.S., BeNewe, France Received 16 July 1971
of
The observation of intensz b&d systems attributable
to Xe2 gives clear spectroscopic evidence of the formation
moleculeseven at 10~~ preuure.
I. introduction
ground was the triggered vacuum spark source [ 1 I] producing an intense continuum in the whole investigated region. A11 experiments have been done at room
There has been revived interest in the ekctronic
structureof tare gas diatomic molecules both from
temperature; with abso~tion cells 92 mm and 200 mm long. The pressure was varied between 1 and 300 torr. The wavelengths accuracy is + 0.2 ?i but the dif:
theoretical and experimental aspects [I-S], with most of the expedmentaI results related to emission spectra, Spectroscopic evidence of molecufar absorption bands has been given recently by Tanaka and Yoshino for I-k2 and Ar2 [6,7] using the helium emission continuum as a background, but the Iack of a convenient source for the spectral range 1300: 1000 A made it difficuft to study krypton and xenon, While studying atomic interaction effects [8] we have reported earlier the description of some bands appearing in the absorption spectrum of xenon, between 1300 and 1250 A, at pressures less than one atmosphere [SJ . The purpose of this paper. is to anaIyse the specific contribution of Xe, molecuIes to the absorption spectrum behveqn 1470 and 1150 a, where we-observe several abso~tion band structures,
fuseness of some bands precluded the determination of their position with this precision.
3. Results and discussion Fig. I reproduces the microphotometer trace of a part of the absorption spectrum, obtained with a pressure example
of 150 torr in the 200 mm cell, and gives an of the con&exity of the xenon spectrum.
The various spectra obtained exhibit the following es- : sential features: i: (i) conside;abIe droadening of the atomic lines, (ii) new fines associated .with atomic transitions 191, : : .(iii) appearance of mobcular band structures (SW
similar to thoseobtained by Tanaka for argon [7]. The results are tentatively discussed in relation to the qualita~i~ potential cuties given by MuIlik& [IO] .
terns I to IV). J_J_.sjs&m
:
l
..,I
,,
:. .. . ‘;,‘. : ‘.‘1
.$ This band system (table 1) appears on the long ,,wavelength side of the first resonance line (1469.6 A) .,:I .i: :: for a x+on pressure of 50 torr in the 200 mm &Ii. Among the four tiolecular’&ates lu;l& Ou+ and ‘&+ .,!s:
correlated with tlie atomic levels 5p6 lSb (Xe), and 6s(312)? (Xe)*, only the OGfstate,cari. be the uptier
‘l’ ohe of this
I, .. .i. ._’
,..,’
,.
:,.. ,? .i.l;:’
....-!z
..& since it.is:the only stable state to _-.’; ., ,:__ :..:.t: ‘. ., :. .,‘. :. .‘-. (. ;’ ‘-‘L .-z, 7 : - . .. .: :. I’.:,-> .-+.‘:- ., : ..:G._‘<. ._ : .’ ,..-
&s&m;
15 February ,1972
CHEIlICAL PHYSICS LETTERS
Volume’ 13. number 2 Tad!; 1
JYavelengths, wavenumbers and vibrational spacingsOf SYSterns I and II, respectively related to the lines 1469.6 A and 1295.6 A I
II
6s(3/2)‘: 1469.6 68045 1483.7 67 399 1484.9 67 344 55 ;;t;:; “6;;;; 63
6s(1/2):
1295.6 1302,9 1303.4 1304.3 1303.8 1304.8
77185 76752,3,-, 76722 23 76699 76669 3O 76640 2g
principle, the transitions originatjng from the minimum of the ground state cui-ve,or nearly so; fqll.on ‘. the right side of the excited curve, far from its niinimum, so that high vibrational levels can be excited. When the pressure is increased a diffuse band appears at 1492.8 A, possibly due to an allqwed transition between the ground state and the lu stable molecular
state. The excited state involved is one of .the six states resulting from the combination atomic terms 5p 6 ‘So ‘and 6s(3/2)!.
of the two
3.2. System II This_s$tem (table 1) is located in the red wing of the second resonance line 5p6 .lSo -+ 6s’(1/2): (A= which transition from the ground state is allowed. As seen from Mulliken’s paper [lo] the minima of most of the potential curves related to the excited states are at shorter interatomic dist,ancesR, (= 2.85 8) than the minimum of the ground state curve (R, x 4.5 A); consequently, due to the Franck-Condon
1295.6
A). The system
appears
at a pressure
of 4-O
torr in the 200 mm cell, the bands being ver$ close to each other, and the resolution of 0.2 .%was barely sufficient to permit the analysis of this system. When the pressure is increased above 60 torr they seem to overlap.
Xe L=200
mm
P=lSO Tan’
i
: Fig. I. Microphotqmeter .,.
..
trace of the xenon absorption spectrum between 1300 A.and i 160 A- @= 150 torr; I= 200 mm). ,..I _ . i .. : ., .,
.‘-
159 ‘.
‘I :’ ,,voi;~e;:i3,,nii~~ei’*
.’
.:
-.
15 February
1972
ci-mirti~ PHY~Ics.LE?TERS L ‘. :, ,.,;, ._. ., : , ., : _‘._,’ : .. . . .._. .’ : :‘..-’ ; ~~.;.~i;ibn~:th.e:.~diecuIar statei resulting from the.tw& :TabIe 2 faiomic, ;g&; $ Wavelen&hs, waGenumbers and vibrational spacings of s&-’ 6’1’SO-:&d 6s’jIj2)!$, only-Ou+ tid lu .’
terns III and IV, related tb ihe line 1192.0 A
.!c&‘~ombi&‘&with.the ground state. As.the lti state is G,.ie@&ive ofie; a& as the potential energy df Ou’ has ‘i -&-ysha~o~ nji+&m [lo] at a relatively large R ‘&_k&.observed bands are well explained by- tran, .‘sition_S‘to the.&+ state, with a Hieli depth of approxikateij 606 crn-l;wd tibrational spacings smaller ‘.than.for tht: tither ekcired stares, as expected from, IheRzw, = con&t r&e [ 121. ._-
III
.'
54(3/2):
,3.3. Sjqteti III ‘:A.inic;ophotqmeter trace of this system is reproduced in fig. 2. This system (table 2) appears very clearly on the red wing of tht line 5p6 ISo +5d(3/2)! (A b-1 19T.O.A) at pressures between 10 and 30 torr ..
Ffg. 2. Mlaophotomettk
16g
L= 92n
1
otr
tram: of system iI! (p = .lm tom: ‘!I= 92 mm). .: , ., ., ” _.’ ‘..-
.. ..F&. 3. :
‘,,
83890
Sd(3/2):
1192.0 1186.0
83890 84317
8S
:;g;
ii;;;
71
,’ 1189:l 84097 ;;
‘-.,
P=‘lOO
1192.0
:Iv
:
‘,
1189.9
84040
56
;;;p;
;;;;;:
36
Volu&e 13,‘numbkr 2
Cf%hf!CAi
.’
P&&C’S
.
.‘.
in the 200 mti,ceII. The combination df the two atomic. terms Sp 6 ‘SO and 34(3/2): gives rise to four moIecul&-states, 1ti, Ig, OU+ and Og’, one of~&ch .wouId be the upper state O$ the observed transition. ‘,
J_EnERS
.. ...
;
,1.5 Fitbruary f97i :: ,. ,.‘~ : ‘,’ .., :, .::: . .. stud$d. [$I ; or.by thk change of ar@&rriom~ntiti .AJ. At low ‘Ijregure ‘(p =, 1 to&; I = 200 r&n).we“c&-,, ,I : seg iri’.the $%jtj; Qf some allowed jiries ti sharp-line :. ..’
that may be of the sake’nature as’satellites’obsetied ‘,
Furthki analysis of this system will ‘begiven in’s forthcorriing paper. Shortly, frbm the .relative posi- :’ fions of ground and excited state curves, it is possible to say that the apparent ~brational spacings observed (70 to 90 cm-“) are somewhat different from the true vibrational spacings of the excited state (approximately50cmW1)_ : ‘, 3.4 System fV
This band system reproduced in Gg. 3, is found on the blue side of the 1192.0 A atomic line; and, as no other nearby atomic level exists, ‘this system is associated with this line. Further this band system exhibits M anomalous convergence towards the long wavelefigths. Mufliken’s caIcuIation of the first order disper-
” :
+f%ese preliminary .r&ui ts &mit us tb bropose tent&ve shapes of potentjal energy curves of some i;noiecuiar excited states-in agreement with the q&litative theoretical potential,curves given by Mulliken, ii01 .& more complete study wiil be the object of a forthcorn- ’ ing pap&. :
References : :
.,
sion forces shows that the Iu molecular state must be pushed up at medium interatomic distances, giving o hump above the asymptote. The shortest wavelength band appears as the sharpest and the most intense so thar we assign Y”= 0 to it. This band being at 430 cm-l from the atomic
Y. Tanaka, J. Opt. Sot. Am. 45 (19.55) 710.‘ R.E. Huffman, J.C. Larrabee and Y. ~%w&a. Appl. Opt 4 (1965) 1581. R.C. Michaelson and A.i. Smith, Chem.’ Phys. Letters 6 (1970) 1.
line, assuming a.welI depth of 200 cm-l
I.V. Kosinkaya and L-P. Potozova, Opt i Spektroskopiya 30 (1971) 853. Y. Tanaka and K. Yoshino, J. Chem. Phys. id (i969) 3087_ ‘. Y. Tanaka and K. Yoshino, J. Chem; Phys. 53 (1970). 2012. KC. Cas:ew, R. Gra&er and J. Romand, Compt. Rend: Acad. Sci. (Paris) 2688 (1969) 552. M-C..Ca+u, Compt Rend. &ad. Sci {P&is) 2708 (1970) 207. R. Mulliken, J. Chem. Phys S2 (197Oj 5170. H. Damany, J.-Y. Ronctn and N. pamany, AppL’Opt. 5 (19661 297. G. Herzberg, Spectra of diatomic m&e&es (Van Nostrand, Princeton, 1950) p_ 456.
for the ground state, the hump is found to be about 200.230 cm- 1. Here also the application of the FranckCondon principIe expIains the apparent antimalous convergence of the band system. Moreover the relative positions of theexcited and ground state curves lead to true vibratipna1 spacings of the upper state decreasing norm&!:ji with increasing Y’. 3.5. utirrer bonds In addition to molecular systems we observe Sev-, craI bands that: may be associated with transitions forbidden, either by parity as the one %e have already
A, Shardazand, J. Quartt. Spectry. Radiative Transfer 8 (1968) 1533.
.:
.’ ..” ., ‘. :: ,. _‘. .‘, ‘. ‘. _.,. ., ., ‘. .,‘.
.,
‘.. .’
: :
‘,
.:
,’ ,‘.
. .
_. ,. .~ ..,
,‘.
13,
number 2
&EMICAL
15 February 197i “
PHYSICS‘ LETTERS : :
‘....
ABSORPTION SPEkTRUM OF THE.XENON MOLECULE IX THE VACUUM UL?kbIdLET REGIONM.-C. CASTEX 2ind N. SAMANY Lubom~oire desHautes Pressions, C.N.R.S., BeNewe, France Received 16 July 1971
of
The observation of intensz b&d systems attributable
to Xe2 gives clear spectroscopic evidence of the formation
moleculeseven at 10~~ preuure.
I. introduction
ground was the triggered vacuum spark source [ 1 I] producing an intense continuum in the whole investigated region. A11 experiments have been done at room
There has been revived interest in the ekctronic
structureof tare gas diatomic molecules both from
temperature; with abso~tion cells 92 mm and 200 mm long. The pressure was varied between 1 and 300 torr. The wavelengths accuracy is + 0.2 ?i but the dif:
theoretical and experimental aspects [I-S], with most of the expedmentaI results related to emission spectra, Spectroscopic evidence of molecufar absorption bands has been given recently by Tanaka and Yoshino for I-k2 and Ar2 [6,7] using the helium emission continuum as a background, but the Iack of a convenient source for the spectral range 1300: 1000 A made it difficuft to study krypton and xenon, While studying atomic interaction effects [8] we have reported earlier the description of some bands appearing in the absorption spectrum of xenon, between 1300 and 1250 A, at pressures less than one atmosphere [SJ . The purpose of this paper. is to anaIyse the specific contribution of Xe, molecuIes to the absorption spectrum behveqn 1470 and 1150 a, where we-observe several abso~tion band structures,
fuseness of some bands precluded the determination of their position with this precision.
3. Results and discussion Fig. I reproduces the microphotometer trace of a part of the absorption spectrum, obtained with a pressure example
of 150 torr in the 200 mm cell, and gives an of the con&exity of the xenon spectrum.
The various spectra obtained exhibit the following es- : sential features: i: (i) conside;abIe droadening of the atomic lines, (ii) new fines associated .with atomic transitions 191, : : .(iii) appearance of mobcular band structures (SW
similar to thoseobtained by Tanaka for argon [7]. The results are tentatively discussed in relation to the qualita~i~ potential cuties given by MuIlik& [IO] .
terns I to IV). J_J_.sjs&m
:
l
..,I
,,
:. .. . ‘;,‘. : ‘.‘1
.$ This band system (table 1) appears on the long ,,wavelength side of the first resonance line (1469.6 A) .,:I .i: :: for a x+on pressure of 50 torr in the 200 mm &Ii. Among the four tiolecular’&ates lu;l& Ou+ and ‘&+ .,!s:
correlated with tlie atomic levels 5p6 lSb (Xe), and 6s(312)? (Xe)*, only the OGfstate,cari. be the uptier
‘l’ ohe of this
I, .. .i. ._’
,..,’
,.
:,.. ,? .i.l;:’
....-!z
..& since it.is:the only stable state to _-.’; ., ,:__ :..:.t: ‘. ., :. .,‘. :. .‘-. (. ;’ ‘-‘L .-z, 7 : - . .. .: :. I’.:,-> .-+.‘:- ., : ..:G._‘<. ._ : .’ ,..-
&s&m;
15 February ,1972
CHEIlICAL PHYSICS LETTERS
Volume’ 13. number 2 Tad!; 1
JYavelengths, wavenumbers and vibrational spacingsOf SYSterns I and II, respectively related to the lines 1469.6 A and 1295.6 A I
II
6s(3/2)‘: 1469.6 68045 1483.7 67 399 1484.9 67 344 55 ;;t;:; “6;;;; 63
6s(1/2):
1295.6 1302,9 1303.4 1304.3 1303.8 1304.8
77185 76752,3,-, 76722 23 76699 76669 3O 76640 2g
principle, the transitions originatjng from the minimum of the ground state cui-ve,or nearly so; fqll.on ‘. the right side of the excited curve, far from its niinimum, so that high vibrational levels can be excited. When the pressure is increased a diffuse band appears at 1492.8 A, possibly due to an allqwed transition between the ground state and the lu stable molecular
state. The excited state involved is one of .the six states resulting from the combination atomic terms 5p 6 ‘So ‘and 6s(3/2)!.
of the two
3.2. System II This_s$tem (table 1) is located in the red wing of the second resonance line 5p6 .lSo -+ 6s’(1/2): (A= which transition from the ground state is allowed. As seen from Mulliken’s paper [lo] the minima of most of the potential curves related to the excited states are at shorter interatomic dist,ancesR, (= 2.85 8) than the minimum of the ground state curve (R, x 4.5 A); consequently, due to the Franck-Condon
1295.6
A). The system
appears
at a pressure
of 4-O
torr in the 200 mm cell, the bands being ver$ close to each other, and the resolution of 0.2 .%was barely sufficient to permit the analysis of this system. When the pressure is increased above 60 torr they seem to overlap.
Xe L=200
mm
P=lSO Tan’
i
: Fig. I. Microphotqmeter .,.
..
trace of the xenon absorption spectrum between 1300 A.and i 160 A- @= 150 torr; I= 200 mm). ,..I _ . i .. : ., .,
.‘-
159 ‘.
‘I :’ ,,voi;~e;:i3,,nii~~ei’*
.’
.:
-.
15 February
1972
ci-mirti~ PHY~Ics.LE?TERS L ‘. :, ,.,;, ._. ., : , ., : _‘._,’ : .. . . .._. .’ : :‘..-’ ; ~~.;.~i;ibn~:th.e:.~diecuIar statei resulting from the.tw& :TabIe 2 faiomic, ;g&; $ Wavelen&hs, waGenumbers and vibrational spacings of s&-’ 6’1’SO-:&d 6s’jIj2)!$, only-Ou+ tid lu .’
terns III and IV, related tb ihe line 1192.0 A
.!c&‘~ombi&‘&with.the ground state. As.the lti state is G,.ie@&ive ofie; a& as the potential energy df Ou’ has ‘i -&-ysha~o~ nji+&m [lo] at a relatively large R ‘&_k&.observed bands are well explained by- tran, .‘sition_S‘to the.&+ state, with a Hieli depth of approxikateij 606 crn-l;wd tibrational spacings smaller ‘.than.for tht: tither ekcired stares, as expected from, IheRzw, = con&t r&e [ 121. ._-
III
.'
54(3/2):
,3.3. Sjqteti III ‘:A.inic;ophotqmeter trace of this system is reproduced in fig. 2. This system (table 2) appears very clearly on the red wing of tht line 5p6 ISo +5d(3/2)! (A b-1 19T.O.A) at pressures between 10 and 30 torr ..
Ffg. 2. Mlaophotomettk
16g
L= 92n
1
otr
tram: of system iI! (p = .lm tom: ‘!I= 92 mm). .: , ., ., ” _.’ ‘..-
.. ..F&. 3. :
‘,,
83890
Sd(3/2):
1192.0 1186.0
83890 84317
8S
:;g;
ii;;;
71
,’ 1189:l 84097 ;;
‘-.,
P=‘lOO
1192.0
:Iv
:
‘,
1189.9
84040
56
;;;p;
;;;;;:
36
Volu&e 13,‘numbkr 2
Cf%hf!CAi
.’
P&&C’S
.
.‘.
in the 200 mti,ceII. The combination df the two atomic. terms Sp 6 ‘SO and 34(3/2): gives rise to four moIecul&-states, 1ti, Ig, OU+ and Og’, one of~&ch .wouId be the upper state O$ the observed transition. ‘,
J_EnERS
.. ...
;
,1.5 Fitbruary f97i :: ,. ,.‘~ : ‘,’ .., :, .::: . .. stud$d. [$I ; or.by thk change of ar@&rriom~ntiti .AJ. At low ‘Ijregure ‘(p =, 1 to&; I = 200 r&n).we“c&-,, ,I : seg iri’.the $%jtj; Qf some allowed jiries ti sharp-line :. ..’
that may be of the sake’nature as’satellites’obsetied ‘,
Furthki analysis of this system will ‘begiven in’s forthcorriing paper. Shortly, frbm the .relative posi- :’ fions of ground and excited state curves, it is possible to say that the apparent ~brational spacings observed (70 to 90 cm-“) are somewhat different from the true vibrational spacings of the excited state (approximately50cmW1)_ : ‘, 3.4 System fV
This band system reproduced in Gg. 3, is found on the blue side of the 1192.0 A atomic line; and, as no other nearby atomic level exists, ‘this system is associated with this line. Further this band system exhibits M anomalous convergence towards the long wavelefigths. Mufliken’s caIcuIation of the first order disper-
” :
+f%ese preliminary .r&ui ts &mit us tb bropose tent&ve shapes of potentjal energy curves of some i;noiecuiar excited states-in agreement with the q&litative theoretical potential,curves given by Mulliken, ii01 .& more complete study wiil be the object of a forthcorn- ’ ing pap&. :
References : :
.,
sion forces shows that the Iu molecular state must be pushed up at medium interatomic distances, giving o hump above the asymptote. The shortest wavelength band appears as the sharpest and the most intense so thar we assign Y”= 0 to it. This band being at 430 cm-l from the atomic
Y. Tanaka, J. Opt. Sot. Am. 45 (19.55) 710.‘ R.E. Huffman, J.C. Larrabee and Y. ~%w&a. Appl. Opt 4 (1965) 1581. R.C. Michaelson and A.i. Smith, Chem.’ Phys. Letters 6 (1970) 1.
line, assuming a.welI depth of 200 cm-l
I.V. Kosinkaya and L-P. Potozova, Opt i Spektroskopiya 30 (1971) 853. Y. Tanaka and K. Yoshino, J. Chem. Phys. id (i969) 3087_ ‘. Y. Tanaka and K. Yoshino, J. Chem; Phys. 53 (1970). 2012. KC. Cas:ew, R. Gra&er and J. Romand, Compt. Rend: Acad. Sci. (Paris) 2688 (1969) 552. M-C..Ca+u, Compt Rend. &ad. Sci {P&is) 2708 (1970) 207. R. Mulliken, J. Chem. Phys S2 (197Oj 5170. H. Damany, J.-Y. Ronctn and N. pamany, AppL’Opt. 5 (19661 297. G. Herzberg, Spectra of diatomic m&e&es (Van Nostrand, Princeton, 1950) p_ 456.
for the ground state, the hump is found to be about 200.230 cm- 1. Here also the application of the FranckCondon principIe expIains the apparent antimalous convergence of the band system. Moreover the relative positions of theexcited and ground state curves lead to true vibratipna1 spacings of the upper state decreasing norm&!:ji with increasing Y’. 3.5. utirrer bonds In addition to molecular systems we observe Sev-, craI bands that: may be associated with transitions forbidden, either by parity as the one %e have already
A, Shardazand, J. Quartt. Spectry. Radiative Transfer 8 (1968) 1533.
.:
.’ ..” ., ‘. :: ,. _‘. .‘, ‘. ‘. _.,. ., ., ‘. .,‘.
.,
‘.. .’
: :
‘,
.:
,’ ,‘.
. .
_. ,. .~ ..,
,‘.