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Electron impact cross sections of some spectral lines and excited states of Hg+ and Hg2+
Volume 118, n u m b e r 5
PHYSICS LETTERS A
20 October 1986
ELECTRON IMPACT CROSS SECTIONS OF SOME SPECTRAL LINES A N D E X C I T E D S T A T E S O F H g ÷ A N D H g 2+ K BLAGOEV and N DIMITROV lnstttute of Sohd State Phvsws, Bulgarmn Academy of Scwnces, Blvd Lemn 72 1784 Sofia Bulgaria R e c e w e d 3 July 1986, revtsed m a n u s c r i p t received 3 S e p t e m b e r 1986, accepted for pubhcat~on 5 S e p t e m b e r 1986
Optical excitation funcUons o f some Beutler spectral hnes of rig ~ and Hg 2+ were o b t a i n e d The effective cross sections in their m a x i m a were m e a s u r e d and the cross sections of 5d%s 2 of Hg -~~ were d e t e r m i n e d C o n s M e r a n o n s about the Hg 2 * laser mechanism are m a d e
The present work xs d e d i c a t e d to the e x o t a n o n funcnons o f some Hg + and Hg 2+ spectral hnes m the case o f direct electron exc~tanon from the ground state of a t o m i c mercury We also have measured the electron ~mpact excltanon effecnve cross secuons (Q,~) o f these spectral lines and, whenever it was possible, the electron i m p a c t cross sectmn (Q,) o f e x o t e d states g w m g rise to the investigated spectral hnes These data are o f particular interest for different gas discharges including some laser systems The cross section (Q,) o f the electron i m p a c t e x o tanon defines the changes m the population o f a g~ven excited state d u n n g that process In general, to obtain the excited state cross sechon, all cascade translUons to the mvesngated state have to be taken into account and the effective cross sections (Q,~) o f all spectral hnes belonging to them, should be s u m m a r i z e d The Hg ÷ spectral hnes originate from 5d96s7s 45/2 and 5d96s7s 55/2 excited states which belong to the Beutler system o f terms [ 1,2 ] These states are close to the second l o m z a t l o n limit defined by the 5dJ°n/ doublet system o f terms The intensity o f the investigated spectral hnes is c o m p a r a b l e to that o f the spectral hnes o f low lying 1°-40 Beutler states [ 1 ] Therefore, the 45/2 and 55/2 states should play an i m p o r t a n t role for the p o p u l a t i o n o f the excited 5d96sn/states o f rig + Here we a d o p t the most commonly used designations [ 1,2] (We should point out that the class~ficauon o f Beutler states m relation to the electronic configurations and spectral hnes o f the 232
5dV6snl system o f terms in our o p l m o n ts far from its c o m p l e n o n ) That IS why it should be useful to d e t e r m i n e the electron ~mpact effecnve cross sections (Q,h) o f these spectral hnes together with the cross secnon (Q,) o f 4s/2 a n d 55/2 states We also studied some spectral lines o f Hg 2+ They originate from Beutler states belonging to the 5d86s 2 electron configuration which is f o r m e d when one m o r e electron from the 5 d 9 c o r e ~s excited At electron energies between 150 and 250 eV and mercury pressures m the m T o r r range the intensity o f these spectral hnes is c o m p a r a b l e w~th that of the strong atomtc mercury spectral hnes The m e a s u r e m e n t s o f the o p n c a l e x o t a t l o n funcUpns were carried out with a three grid Hanle-type electron gun The current density o f the cyhndrlcal electron b e a m with a d i a m e t e r o f 2 m m was 12 A / m 2 The electron energy distribution energy d i d not exceed 1 0 eV This was completely satisfying since the purpose o f the present work was to measure the o p n c a l e x c l t a n o n funcnons m a wide range o f energtes a n d to d e t e r m i n e the effective cross secuons m thew m a x i m a The pressure o f the saturated vapours was d e t e r m i n e d by the t e m p e r a t u r e of the cell reservoir with natural ~sotope mercury m~xture The temperature was m a i n t a i n e d w~th a preclsmn o f 0 5 °C The m e a s u r e m e n t s o f Hg + spectral line excttaUon functions were p e r f o r m e d at a pressure o f 3 m T o r r The spectral hnes were separated with a grating mon o c h r o m a t o r M D R - 2 with dlspersmn 2 A and were 0 375-9601/86/$ 03 50 © Elsevier Science Pubhshers B V (North-Holland Physics Pubhshmg Division)
Volume 118, number 5
PHYSICS LETTERS A
tral hnes [6,7] have been used to d e t e r m i n e the effective cross sections from optical excitation functtons F o r this procedure the sensmvaty o f the reg~stratmg system was c a h b r a t e d in region 2 2 0 0 - 3 5 0 0 ~, wath a hydrogen l a m p and in the anterval 3500-8000 A w~th a tungsten l a m p The results for the effecuve cross sections at an energy o f 130 eV are s u m m a r i z e d in table 1 Three types o f errors contribute to effecttve cross secttons errors stattstlcs, callbraUon o f the regastratmg system and atomic effecuve cross section The total effecuve cross-sect~on errors do not exceed 40% To d e t e r m i n e the electron impact cross sections (Q,) o f the excited states it ts necessary to know the cascade repopulatlon and the branching rataos o f all spectral lanes belonging to these states In our experiment the presence o f cascade p o p u l a u o n to the investigated states was controlled by the time decay curves o f the populaUon after pulsed excltatton In fact, the excated state hfet~mes were measured The delayed-coincidence m e t h o d with t l m e - a m p h t u d e conversion and subsequent pulse height analysts and storage m a multtchannel analyzer was e m p l o y e d In that case a negattve bins voltage and posatwe rectangular pulses were a p p h e d on the second grad o f the
recorded m the whole spectral regaon by a p h o t o m u l tapller FEU-106 e m p l o y e d in the p h o t o c o u n t l n g regame Some Hg + optical excltat~on functions are presented m fig 1 They are s~mllar to those o f the spectral hnes o f low lying Beutler states 1°-4 ° reported by Varshavskn et al [3] The e x o t a t l o n functaons ancrease to 120 eV and have shghtly expressed maxama at an energy between 130 and 150 eV The optical excttataon funcuons o f the spectral hnes from states o f the 5d~°nl doublet as well as from the Beutler 5d96snl system o f terms were reported an ref [4] F o u r o f the opUcal exotat~on functions reported m ref [4] concern spectral hnes o f the 45/2 state [ 5] H o w e v e r three o f them have been wrongly classified and according to a more rehable classafication [1 ] these spectral hnes do not refer to the 5d96s7s 45/2 state Therefore at is not surprising that a different excataUon functmn shape for both spectral lanes o f the 45/2 state is reported [4] The fourth spectral lane, 3914 3 /~ (45/2-2F~/2), m e a s u r e d by Semenova a n d S m l r n o v [4], as very weak at our experimental c o n d m o n s and therefore ~t was tmpossable to carry out any m e a s u r e m e n t s The well-known effective cross secUons for 4358, 3650, 2967 and mainly 5461/k mercury atomic spec-
Qik~10-19 crn2
•
20 October 1986
•
5~0 /
e
/
2947A
•
D
/
/ / 2)5
/ •
"-.-.... •
.....,.
/ / " •
I / /
----- ...._ ._.._. ___.
' /
3208 1 ....
-{-
.__
.
,/ ,
2935 ,~ I
100
t
I
t
200
" ""-• I
300 E~ eV
Fig 1 Optical e×otat~on Functions of some spectral hnes of rig"
233
Volume 118, number 5
20 October 1986
PHYSICS LETTERS A
Table 1 Effecuve cross sechons of some Hg ~ spectral hnes (data ]n 10 ~9cm-') State
E (cm ')
Transition
2 (•)
Q,h
Q,
55~
140134
5~/2-24~/2 5s/2-23°/, 5~,,-22~
3549 3451 3385 3208 2947 2935 3264 2414 2407
0 42 0 52 0 40 22 53 11 0 21 0 42 0 47
)9 9
5s;3-20°/2 5v~- 16q/_~ 5s/~-I 5o/2
4s/,_
4s/2-15°/2
136711
45,2- 8~/2 45/2- 7~/,
electron gun The pulse duration depends on the hfettmes o f the investigated states F o r 45/2 and 55/2 we used l0 ns More detads o f the experimental set up and the data processing is given in ref [8] In hfetime m e a s u r e m e n t s the procedure o f cascade populatmn extractmn is well d e v e lo p e d cascade population of a few percent o f the total p o p u l a t m n of the investigated states can be taken into account [9,10] Th e 4v2 and 5s/2 cross section estimates were pe r form ed assuming that there was no cascade pop-
>I 1 1
ulatton on these states Thts assumption was verified by measuring the hfet]mes o f these states at electron excltatmn energies up to 300 eV Besides the investigated spectral lines, there are also ultravmlet (below 2 0 0 0 / ~ ) t r a n s m o n s from 45/2 and 55/2 states to low lying l ° - 4 o Beutler states Smce their wavelength ts shorter than the low h m l t o f our experimental set-up sens~twlty, we could not d e t e r m m e their effecuve cross secuons and consequently the 45/2 and 55/2 cross sectmns That is why m table 1 only the lower limits
b Q'k.~ 10-15 c m 2
f
,o/
10
4797~
/
/ / /
/ /
t
/ / I
/ / /
o ,se
./..:5 ¢'.,. ~ l ~
~"
6501 ,~
5"-" " I
100
,
I
200
,
I
Fig 2 Optical exotatlon functions of Hg-'~ 5d86sZ-5d96p spectral hnes 234
L
300 E~ eV-
Volume 118, number 5
20 October 1986
PHYSICS LETTERS A
Table 2 Hg" spectral hne effective cross sections (Q,h) and excited state cross sections (Q,) (data m 10 ~8cm 2) State
L (cm t)
Transition
) (A)
Q,~
11_~
118926
10~ 124 13_~
122735 126468 133731
14.
158909
11_~-1" 11 .-2'~ 10t-l'~ 12~-2'~ 13 -1'~ 13 -2(~ 13 ,-3~ 132-4~' 13_-6~ 14N-8'~)
6501 7517 5210 4797 3312 3557 6584 6610 7808 3090
13 0 18 19 10 9 21 14 0 34 0 17 0 25 13
o f these d a t a are s h o w n T h e c o n t r i b u t i o n s o f w e a k spectral hnes m the w s l b l e spectral r e g m n did not e x c e e d 10% In the p r e s e n t w o r k we h a v e m e a s u r e d the optical e x c l t a t m n f u n c t i o n s o f ten 5dS6s2-5d96p spectral lines o f Hg 2+ T h e 5dS6s 2 e l e c t r o n c o n f i g u r a t m n consists o f eight states Spectral h n e s f r o m part o f t h e m to 5d96p states were o b s e r v e d [ 11 ] T h e r e are no o t h e r t r a n s i t m n s f r o m 5dS6s 2 states to low lying H g 2+ states In fig 2 4797, 3312 a n d 5210 ]t spectral hne optical e x c t t a t m n f u n c t m n s are shown T h e y h a v e wide m a x i m a m the 1 8 0 - 2 5 0 eV r e g m n T h e effect i v e cross-section values at an energy o f 180 eV are p r e s e n t e d m table 2 0 p t t c a l excttat~on f u n c t i o n s o f ten spectral lines b e l o n g i n g to the 4dS6s 2 e l e c t r o n c o n f i g u r a t i o n o f C d 2+ h a v e recently b e e n r e p o r t e d [ 12 ] T h e y h a v e the s a m e shape as the Hg -~÷ optical e x c i t a t i o n f u n c t i o n s m e a s u r e d in the p r e s e n t w o r k T h e r e are no t r a n s m o n s f r o m states o f h~gher lying e l e c t r o n c o n f i g u r a t i o n s to the 14o state [ 11 ] O n the o t h e r h a n d we d i d not observe transitions f r o m 5d'~6p states e~ther to 5d86s 2 or 5d96s states T h e absence o f cascade r e p o p u l a h o n was also c h e c k e d by m e a n s o f a d e l a y e d - c o i n c i d e n c e m e t h o d at e l e c t r o n e x c i t a t i o n energies up to 300 eV H e n c e , in table 2 the e l e c t r o n ~mpact cross sections o f the 5 d % s 2 H g 2 ~ states are p r e s e n t e d In o u r e x p e r i m e n t we c o u l d not reglstrate the spectral line 2480 A f r o m the 140 state A n o t h e r line, 4181 A, f r o m the s a m e state has a t w o - s t e p e x o t a t i o n f u n c t i o n shape T h e first o f t h e m begins at 12 eV, w h d e the s e c o n d o n e a p p e a r s at 50 eV Thus, this h n e m i g h t c o l n o d e with the a t o m i c one So, the v a l u e o f the 140 state cross section m table 2 is an e s t i m a t e ,
Q, 1 48 19 10 9 4 26
13
but the p r o b a b l e c o n t r i b u t i o n o f the 4181 A e f f e c t i v e cross section dtd not e x c e e d 2% It s h o u l d be n o t e d that the m e a s u r e d v a l u e s o f H f + excited states cross sections (as well as Cd 2 + e f f e c t i v e cross-section d a t a [ 12 ] ) are rather surprising since in this case a c o m p l e t e r e a r r a n g e m e n t o f the 5d~°6s -~ e l e c t r o n structure has to be r e a h z e d , o r two electrons h a v e to be k n o c k e d o u t f r o m the i n n e r 5d ~° core T h e large values o f i n v e s t i g a t e d H g 2+ spectral lines e f f e c t i v e cross sections e x p l a i n the large intensities o f t h o s e spectral hnes, since they h a v e transit i o n p r o b a b l h t t e s m the range o f ( 2 0 - 0 1 ) × 10 ~ s [13] Both spectral h n e s 6501 a n d 4797 A are I m p o r t a n t m c o n n e c t i o n with laser a c t i o n T h e f o r m e r ~s o b t a i n e d m pure Hg pulse discharge [ 14], a n d the latter m H e - H g m i x t u r e lasers [ 15] A c c o r d i n g to the cross-section data o b t a i n e d m the present work, direct electron e x c i t a t i o n for u p p e r laser levels m i g h t be proposed, while this process for l o w e r 5d96p laser levels is less probable, since we did not o b s e r v e the spectral h n e s f r o m these states T h i s m i g h t be the m e c h a n i s m r e s p o n s i b l e for p o p u l a t i o n r e v e r s i o n
References
[ 1] J C McLennon, A B McLay and M F Crawford Proc R Soc 134 (1931) 41 [2] C E Moore, Atomtc energy levels Vol 3 (NBS Washington 1958) [ 3 ] S P Varshavskll A A Mlljurova and N P Penkln Opt Speclrosc USSR 28 (1970) 26 [4] 1 V Semenova and Ju M Sm~rnov Opt Spectrosc USSR 44 (1978) 417 235
Volume 118, number 5
PHYSICS LETTERS A
[5] T S Subbaraya, Z Phys 78 (1932)514 [6] 1 P Bogdanova and V D Marusln, Opt Spectrosc USSR 31 (1971) 339 [ 7 ] H S W Massey, E H S Burhop and H B Gllbody, Electromc and lomc ~mpact phenomena, Vol 1 (Clarendon, Oxford, 1969) [8] K Blagoev, N Dimltrov and M Drenska, J Phys B 17 (1984) 2189 [9] W L W~ese, Progress m atomic spectroscopy, part B (Plenum, New York,1979) p 1101
236
20 October 1986
[ 10] A Corney, Adv Electron Electron Phys 29 (1970) 115 [11] EW Foster, Proc R Soc A208 (1951)368 [12] S Inaba, K Hane and T Goto, Phys Lett A 114 (1986) 201 [ 13] K Blagoev and N DImltrov, Phys Lett A 117 (1986) 185 [14] H R Luthl, W Seehc and A Stadler, IEEE QE 5 (1976) 317 [ 15 ] H J Gerntsen and P V Goedertler, J Appl Phys 35 (1964) 3060
PHYSICS LETTERS A
20 October 1986
ELECTRON IMPACT CROSS SECTIONS OF SOME SPECTRAL LINES A N D E X C I T E D S T A T E S O F H g ÷ A N D H g 2+ K BLAGOEV and N DIMITROV lnstttute of Sohd State Phvsws, Bulgarmn Academy of Scwnces, Blvd Lemn 72 1784 Sofia Bulgaria R e c e w e d 3 July 1986, revtsed m a n u s c r i p t received 3 S e p t e m b e r 1986, accepted for pubhcat~on 5 S e p t e m b e r 1986
Optical excitation funcUons o f some Beutler spectral hnes of rig ~ and Hg 2+ were o b t a i n e d The effective cross sections in their m a x i m a were m e a s u r e d and the cross sections of 5d%s 2 of Hg -~~ were d e t e r m i n e d C o n s M e r a n o n s about the Hg 2 * laser mechanism are m a d e
The present work xs d e d i c a t e d to the e x o t a n o n funcnons o f some Hg + and Hg 2+ spectral hnes m the case o f direct electron exc~tanon from the ground state of a t o m i c mercury We also have measured the electron ~mpact excltanon effecnve cross secuons (Q,~) o f these spectral lines and, whenever it was possible, the electron i m p a c t cross sectmn (Q,) o f e x o t e d states g w m g rise to the investigated spectral hnes These data are o f particular interest for different gas discharges including some laser systems The cross section (Q,) o f the electron i m p a c t e x o tanon defines the changes m the population o f a g~ven excited state d u n n g that process In general, to obtain the excited state cross sechon, all cascade translUons to the mvesngated state have to be taken into account and the effective cross sections (Q,~) o f all spectral hnes belonging to them, should be s u m m a r i z e d The Hg ÷ spectral hnes originate from 5d96s7s 45/2 and 5d96s7s 55/2 excited states which belong to the Beutler system o f terms [ 1,2 ] These states are close to the second l o m z a t l o n limit defined by the 5dJ°n/ doublet system o f terms The intensity o f the investigated spectral hnes is c o m p a r a b l e to that o f the spectral hnes o f low lying 1°-40 Beutler states [ 1 ] Therefore, the 45/2 and 55/2 states should play an i m p o r t a n t role for the p o p u l a t i o n o f the excited 5d96sn/states o f rig + Here we a d o p t the most commonly used designations [ 1,2] (We should point out that the class~ficauon o f Beutler states m relation to the electronic configurations and spectral hnes o f the 232
5dV6snl system o f terms in our o p l m o n ts far from its c o m p l e n o n ) That IS why it should be useful to d e t e r m i n e the electron ~mpact effecnve cross sections (Q,h) o f these spectral hnes together with the cross secnon (Q,) o f 4s/2 a n d 55/2 states We also studied some spectral lines o f Hg 2+ They originate from Beutler states belonging to the 5d86s 2 electron configuration which is f o r m e d when one m o r e electron from the 5 d 9 c o r e ~s excited At electron energies between 150 and 250 eV and mercury pressures m the m T o r r range the intensity o f these spectral hnes is c o m p a r a b l e w~th that of the strong atomtc mercury spectral hnes The m e a s u r e m e n t s o f the o p n c a l e x o t a t l o n funcUpns were carried out with a three grid Hanle-type electron gun The current density o f the cyhndrlcal electron b e a m with a d i a m e t e r o f 2 m m was 12 A / m 2 The electron energy distribution energy d i d not exceed 1 0 eV This was completely satisfying since the purpose o f the present work was to measure the o p n c a l e x c l t a n o n funcnons m a wide range o f energtes a n d to d e t e r m i n e the effective cross secuons m thew m a x i m a The pressure o f the saturated vapours was d e t e r m i n e d by the t e m p e r a t u r e of the cell reservoir with natural ~sotope mercury m~xture The temperature was m a i n t a i n e d w~th a preclsmn o f 0 5 °C The m e a s u r e m e n t s o f Hg + spectral line excttaUon functions were p e r f o r m e d at a pressure o f 3 m T o r r The spectral hnes were separated with a grating mon o c h r o m a t o r M D R - 2 with dlspersmn 2 A and were 0 375-9601/86/$ 03 50 © Elsevier Science Pubhshers B V (North-Holland Physics Pubhshmg Division)
Volume 118, number 5
PHYSICS LETTERS A
tral hnes [6,7] have been used to d e t e r m i n e the effective cross sections from optical excitation functtons F o r this procedure the sensmvaty o f the reg~stratmg system was c a h b r a t e d in region 2 2 0 0 - 3 5 0 0 ~, wath a hydrogen l a m p and in the anterval 3500-8000 A w~th a tungsten l a m p The results for the effecuve cross sections at an energy o f 130 eV are s u m m a r i z e d in table 1 Three types o f errors contribute to effecttve cross secttons errors stattstlcs, callbraUon o f the regastratmg system and atomic effecuve cross section The total effecuve cross-sect~on errors do not exceed 40% To d e t e r m i n e the electron impact cross sections (Q,) o f the excited states it ts necessary to know the cascade repopulatlon and the branching rataos o f all spectral lanes belonging to these states In our experiment the presence o f cascade p o p u l a u o n to the investigated states was controlled by the time decay curves o f the populaUon after pulsed excltatton In fact, the excated state hfet~mes were measured The delayed-coincidence m e t h o d with t l m e - a m p h t u d e conversion and subsequent pulse height analysts and storage m a multtchannel analyzer was e m p l o y e d In that case a negattve bins voltage and posatwe rectangular pulses were a p p h e d on the second grad o f the
recorded m the whole spectral regaon by a p h o t o m u l tapller FEU-106 e m p l o y e d in the p h o t o c o u n t l n g regame Some Hg + optical excltat~on functions are presented m fig 1 They are s~mllar to those o f the spectral hnes o f low lying Beutler states 1°-4 ° reported by Varshavskn et al [3] The e x o t a t l o n functaons ancrease to 120 eV and have shghtly expressed maxama at an energy between 130 and 150 eV The optical excttataon funcuons o f the spectral hnes from states o f the 5d~°nl doublet as well as from the Beutler 5d96snl system o f terms were reported an ref [4] F o u r o f the opUcal exotat~on functions reported m ref [4] concern spectral hnes o f the 45/2 state [ 5] H o w e v e r three o f them have been wrongly classified and according to a more rehable classafication [1 ] these spectral hnes do not refer to the 5d96s7s 45/2 state Therefore at is not surprising that a different excataUon functmn shape for both spectral lanes o f the 45/2 state is reported [4] The fourth spectral lane, 3914 3 /~ (45/2-2F~/2), m e a s u r e d by Semenova a n d S m l r n o v [4], as very weak at our experimental c o n d m o n s and therefore ~t was tmpossable to carry out any m e a s u r e m e n t s The well-known effective cross secUons for 4358, 3650, 2967 and mainly 5461/k mercury atomic spec-
Qik~10-19 crn2
•
20 October 1986
•
5~0 /
e
/
2947A
•
D
/
/ / 2)5
/ •
"-.-.... •
.....,.
/ / " •
I / /
----- ...._ ._.._. ___.
' /
3208 1 ....
-{-
.__
.
,/ ,
2935 ,~ I
100
t
I
t
200
" ""-• I
300 E~ eV
Fig 1 Optical e×otat~on Functions of some spectral hnes of rig"
233
Volume 118, number 5
20 October 1986
PHYSICS LETTERS A
Table 1 Effecuve cross sechons of some Hg ~ spectral hnes (data ]n 10 ~9cm-') State
E (cm ')
Transition
2 (•)
Q,h
Q,
55~
140134
5~/2-24~/2 5s/2-23°/, 5~,,-22~
3549 3451 3385 3208 2947 2935 3264 2414 2407
0 42 0 52 0 40 22 53 11 0 21 0 42 0 47
)9 9
5s;3-20°/2 5v~- 16q/_~ 5s/~-I 5o/2
4s/,_
4s/2-15°/2
136711
45,2- 8~/2 45/2- 7~/,
electron gun The pulse duration depends on the hfettmes o f the investigated states F o r 45/2 and 55/2 we used l0 ns More detads o f the experimental set up and the data processing is given in ref [8] In hfetime m e a s u r e m e n t s the procedure o f cascade populatmn extractmn is well d e v e lo p e d cascade population of a few percent o f the total p o p u l a t m n of the investigated states can be taken into account [9,10] Th e 4v2 and 5s/2 cross section estimates were pe r form ed assuming that there was no cascade pop-
>I 1 1
ulatton on these states Thts assumption was verified by measuring the hfet]mes o f these states at electron excltatmn energies up to 300 eV Besides the investigated spectral lines, there are also ultravmlet (below 2 0 0 0 / ~ ) t r a n s m o n s from 45/2 and 55/2 states to low lying l ° - 4 o Beutler states Smce their wavelength ts shorter than the low h m l t o f our experimental set-up sens~twlty, we could not d e t e r m m e their effecuve cross secuons and consequently the 45/2 and 55/2 cross sectmns That is why m table 1 only the lower limits
b Q'k.~ 10-15 c m 2
f
,o/
10
4797~
/
/ / /
/ /
t
/ / I
/ / /
o ,se
./..:5 ¢'.,. ~ l ~
~"
6501 ,~
5"-" " I
100
,
I
200
,
I
Fig 2 Optical exotatlon functions of Hg-'~ 5d86sZ-5d96p spectral hnes 234
L
300 E~ eV-
Volume 118, number 5
20 October 1986
PHYSICS LETTERS A
Table 2 Hg" spectral hne effective cross sections (Q,h) and excited state cross sections (Q,) (data m 10 ~8cm 2) State
L (cm t)
Transition
) (A)
Q,~
11_~
118926
10~ 124 13_~
122735 126468 133731
14.
158909
11_~-1" 11 .-2'~ 10t-l'~ 12~-2'~ 13 -1'~ 13 -2(~ 13 ,-3~ 132-4~' 13_-6~ 14N-8'~)
6501 7517 5210 4797 3312 3557 6584 6610 7808 3090
13 0 18 19 10 9 21 14 0 34 0 17 0 25 13
o f these d a t a are s h o w n T h e c o n t r i b u t i o n s o f w e a k spectral hnes m the w s l b l e spectral r e g m n did not e x c e e d 10% In the p r e s e n t w o r k we h a v e m e a s u r e d the optical e x c l t a t m n f u n c t i o n s o f ten 5dS6s2-5d96p spectral lines o f Hg 2+ T h e 5dS6s 2 e l e c t r o n c o n f i g u r a t m n consists o f eight states Spectral h n e s f r o m part o f t h e m to 5d96p states were o b s e r v e d [ 11 ] T h e r e are no o t h e r t r a n s i t m n s f r o m 5dS6s 2 states to low lying H g 2+ states In fig 2 4797, 3312 a n d 5210 ]t spectral hne optical e x c t t a t m n f u n c t m n s are shown T h e y h a v e wide m a x i m a m the 1 8 0 - 2 5 0 eV r e g m n T h e effect i v e cross-section values at an energy o f 180 eV are p r e s e n t e d m table 2 0 p t t c a l excttat~on f u n c t i o n s o f ten spectral lines b e l o n g i n g to the 4dS6s 2 e l e c t r o n c o n f i g u r a t i o n o f C d 2+ h a v e recently b e e n r e p o r t e d [ 12 ] T h e y h a v e the s a m e shape as the Hg -~÷ optical e x c i t a t i o n f u n c t i o n s m e a s u r e d in the p r e s e n t w o r k T h e r e are no t r a n s m o n s f r o m states o f h~gher lying e l e c t r o n c o n f i g u r a t i o n s to the 14o state [ 11 ] O n the o t h e r h a n d we d i d not observe transitions f r o m 5d'~6p states e~ther to 5d86s 2 or 5d96s states T h e absence o f cascade r e p o p u l a h o n was also c h e c k e d by m e a n s o f a d e l a y e d - c o i n c i d e n c e m e t h o d at e l e c t r o n e x c i t a t i o n energies up to 300 eV H e n c e , in table 2 the e l e c t r o n ~mpact cross sections o f the 5 d % s 2 H g 2 ~ states are p r e s e n t e d In o u r e x p e r i m e n t we c o u l d not reglstrate the spectral line 2480 A f r o m the 140 state A n o t h e r line, 4181 A, f r o m the s a m e state has a t w o - s t e p e x o t a t i o n f u n c t i o n shape T h e first o f t h e m begins at 12 eV, w h d e the s e c o n d o n e a p p e a r s at 50 eV Thus, this h n e m i g h t c o l n o d e with the a t o m i c one So, the v a l u e o f the 140 state cross section m table 2 is an e s t i m a t e ,
Q, 1 48 19 10 9 4 26
13
but the p r o b a b l e c o n t r i b u t i o n o f the 4181 A e f f e c t i v e cross section dtd not e x c e e d 2% It s h o u l d be n o t e d that the m e a s u r e d v a l u e s o f H f + excited states cross sections (as well as Cd 2 + e f f e c t i v e cross-section d a t a [ 12 ] ) are rather surprising since in this case a c o m p l e t e r e a r r a n g e m e n t o f the 5d~°6s -~ e l e c t r o n structure has to be r e a h z e d , o r two electrons h a v e to be k n o c k e d o u t f r o m the i n n e r 5d ~° core T h e large values o f i n v e s t i g a t e d H g 2+ spectral lines e f f e c t i v e cross sections e x p l a i n the large intensities o f t h o s e spectral hnes, since they h a v e transit i o n p r o b a b l h t t e s m the range o f ( 2 0 - 0 1 ) × 10 ~ s [13] Both spectral h n e s 6501 a n d 4797 A are I m p o r t a n t m c o n n e c t i o n with laser a c t i o n T h e f o r m e r ~s o b t a i n e d m pure Hg pulse discharge [ 14], a n d the latter m H e - H g m i x t u r e lasers [ 15] A c c o r d i n g to the cross-section data o b t a i n e d m the present work, direct electron e x c i t a t i o n for u p p e r laser levels m i g h t be proposed, while this process for l o w e r 5d96p laser levels is less probable, since we did not o b s e r v e the spectral h n e s f r o m these states T h i s m i g h t be the m e c h a n i s m r e s p o n s i b l e for p o p u l a t i o n r e v e r s i o n
References
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