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Observation of a new near-red band of the NaCs molecule
Physics Letters A 159 (1991 ) 266—270 North-Holland
PHYSICS LETTERS A
Observation of a new near-red band of the NaCs molecule A. Kopystynska
~,
C. Gabbanini, S. Gozzini, M. Biagini
Islitulo di Fisica .1 tom Ica e Mo/ceo/are del C’onsiglio j’vaionale del/c Ricerche, Via dcl Giardino 7, 56127 Pisa, flu/i’
and L. Moi Dipartimenlo di Fisica, Universitd di Siena, Via Banchi di Sotto 55, 53100 Siena, halt’ Received 21 May 1991 revised manuscript received 7 August 1991 accepted for publication 13 August 1991 Communicated by B. Fricke
A new near-red band of the NaCs molecule has been observed in a cell containing dense sodium and cesium vapors irradiated 3fl—.a ~ electronic transition. by the 514.5 nm Ar laser line. The band is assigned to the d
1. Introduction Although the diatomic alkali metal spectra have been studied since the very beginning ofthis century, some of the heteronuclear molecules are still very littie known and require further study from both the experimental and the theoretical point of view. More precisely, an up to date review shows that the NaK [1—3],NaLi [4—6]and RbCs [7—9]molecules have been extensively investigated while, besides some old experiments [10,111, there are a few papers on KRb and NaRb [12—17].Finally a detailed analysis of the D 2fl—~X‘~ green band of NaCs has been reported by Diemer et al. [18]. The near-red band of the NaCs molecule reported here has been accidentally observed in a cell contaming a mixture of all alkali metals except lithium and a few Torr of a buffer gas, upon 514.5 nm Ar~ laser line excitation. The whole fluorescence spectrum shows atomic lines and molecular bands due to both radiative decay and energy transfer processes. This is due to the presence of ten different diatomic molecules (Na 2, K7, Rb7, Cs2, NaK, NaRb, NaCs, KRb, KCs and RbCs), besides the atoms, in the vaPermanent address: Institute of Experimental Physics, Warsaw University. ul. Hoza 69. 00681 Warsaw, Poland.
266
por mixture. Therefore the identification of the molecule emitting the red band was not straightforward. The task was complicated not only by the poor knowledge of some of these molecules but also by the fact that the relative vapor densities depend in a complex way both on the initial composition of the metal sample and on the temperature. Therefore it was necessary to prepare and examine many cells filled with various combinations of metal pairs and to analyze many molecular spectra.
2. Experimental apparatus and results An Ar~laser beam, tuned to the 514.5 nm line, crosses an alkali-resistant glass cell that is placed in an oven and is heated up to a temperature of 350°C. The fluorescence is analyzed by a very-large-band apparatus consisting of two monochromators, one covering the 400—8 50 nm wavelength range and the other one the 1—2.5 ~im range. Although the observed spectra in the four alkali cells are very rich and complex, all the lines and bands have been assigned with the exception of the band shown tn fig. 1, which is not reported in literature. The band cxtends from 655.5 to 663.3 nm, i.e. for about 180 cm~,and it consists of only five well distinguished
0375-9601/91 /$ 03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved.
Volume 159, number 4,5
PHYSICS LETTERS A
14 October 1991
0
10
20
30
40
50
60
70
1L (Wfcm2)
Fig. 2. Intensity of the line at ~=657.5 nm versus laser power. Solid line represents the linear regression.
~
6500
j~j~I
6550
~
10
3600
6650
Fig. 1. Spectrum of the near-red band of the NaCs molecule observed in the cell containing Na, K, Rb and Cs, T= 320°C, ‘L= 50 W/cm2.
vibrational transitions at wavelengths equal to 655.5, 657.5, 659.5, 661.4 and 663.3 nm respectively. The mean distance between them is about 46 cm~.The band has also a fine structure, as shown in fig. 1. Each vibrational transition has three rotational components with a mean distance between them of about 7 cm~.This is a signature of a fl—~Itransition. The band intensity depends linearly both on the laser power and on the total vapor density, as shown in fig. 2, where the intensity of the maximum of the band at 2=657.5 nm versus laser power is displayed, and in fig. 3, where the intensity variation of the line at A = 655.5 nm versus the inverse of the temperature T of the cell is plotted, It is important to remark that the band excitation requires rather high laser light power and that there
01
1.65
1.75
1.85
1.95 l/T
(10
~2.05 /K)
Fig. 3~Intensity ofthe line at ~=655.5 nm versus l/T.
is no evidence of fluorescence saturation even with 70 W/cm2. Moreover the linear dependence of the fluorescence intensity on laser power, as shown in fig. 2, indicates that the band is not due to a twophoton excitation process. The linear dependence of the fluorescence intensity on 1 / T, as shown in fig. 3, excludesa collisional origin ofthe band. Another important remark to be given is that the other blue-green Ar~laser lines do not excite this band. Cells fitted with all the possible combinations of alkali atoms were tested and the band was found only in the cell containing Na and Cs. The molecular fluorescence is less intense in this cell and it is observed only at high temperatures (T> 300°C). In the cell filled with Na, K, Rb and Cs, on the other hand, the band is still observed at a temperature of 220°C.This different behaviour is probably due to the relative Cs densities which are very different in these two cells. 267
Volume 159, number 4,5
1
PHYSICS LETTERS A
o~2 NaCs
1 010
~
Na
2
1 1013
1014
~~15
1016
n 1017 (Cs)
(cm 1018 3)
Fig. 4. Plot of the calculated molecular densities as a function of Cs atomic density.
The Cs/Na ratio can be significantly changed by just a small variation of the cesium quantity in the metal deposit of the cell. The relative molecular densities are strongly influenced by the atomic ones and in particular the NaCs/Na 2 ratio increases with the Cs/ Na ratio, as shown in fig. 4. The curves reported in this figure have been calculated by using the rate coefficients for molecular formation and by imposing mass conservation. We experimentally measured the relative atomic densities in the two cells by white light absorption and the Cs/Na ratio was effectively larger in the cell containing Na, K, Rb and Cs. We also checked experimentally that the red band does
14 October 1991
plicated by the total absence of theoretical evaluations of the electronic potential curves. Therefore the identification has been derived according to energy considerations and to the Wigner—Witmer correlation rule, which correlates the molecular electronic levels to the atomic ones (table 1). Our conclusions are that the 514.5 nm Ar~laser line excites both the allowed X ‘~ —~D fl transition and the slightly forbidden X ‘~ —~d3fl transition. After the results shown in figs. 2 and 3, it seems, in 3fl state.population The molecules exfact, unlikely to be a collisional transfer cited from to thethese D ifitwo to states the d decay to the ground state by emitting two bands: a red band which corresponds to the d 3[1—3a 3~±transition and a green molecular band, corresponding to the D ifl~x~f transition. This last one, shown in fig. 5, has been reported for the first time by Diemer et al. [18]. The lowest trip-
~ .~
not finally belong webycame toan theelectronic Na2 to the or Cs2 conclusion molecular that spectrum must and be emitted transition of itthe NaCs molecule.
~ 5300
5500
5400
3. Discussion Fig. 5. Fluorescence spectrum ofthe D fl-.X
The identification of the band transition is corn-
~°
NaCs.
Table I NaCs molecular states, atomic excitation energies E,,,~and correlated atomic States. NaCs ~ 3fl, B fl, c A~ b 3fl, D fl e ~, C~ d311, Gil, h ~ F ‘~, g 3~~ H’~,i
268
E ‘A f3~~
E~(cm~)
Cs
Na
011178—11732 14499—14597 16956—16973 18535
6P 6S SD112377 6S312512 7S
3S 3S 3P, 3S 3S 72,312
green band of
Volume 159, number 4,5
PHYSICS LETTERS A
Table 2 Known spectroscopic constants of the alkali molecule a ~ Molecule
14 October 1991
states.
w,
B,
r,
D,
(cm’)
(cm—’)
(A)
(cm—’)
TI’, (cm’)
Ref. theor.
exp.
7Li 2
66.4 63.73 65.17 73.0
6Li 2 Na2
K2 Rb2 Cs2 LiNa NaK
NaRb NaCs RbCs
24.47 23.14 26.37 11 12(11.2) 39.90 22.82 23,1 23 26.9 22.99086 48.48 46 30.67
0.2743 0.2786 0.329
4.068 4.182 4.154 4.13 5.206 5.3
0.00597 5.731 5.338 6.38 0.0597 0.1390 0.0392 0.0395
0.03936956
4.754 5.457 5.431 5.59 5.180 5.438
5.626
let state of the red band should have a very 3~ shallow ground potential curve, as in the case of the a state in all other alkali metal diatomic molecules (see table 2). The wavelength and the extension of the fluorescence band imply that the a ~ state potential curve of the NaCs molecule is about 4000 cm~ above the minimum of the X ~ ground state potential curve and its potential depth is larger than 200 cm This is consistent with the results of Na—Cs scattering experiments in refs. [19—21].The greenband intensity shows saturation by increasing the laser power density, as it should be for an allowed transition, while the other band does not, supporting the hypothesis that it is excited by a forbidden transition. In ref. [18] the analysis of the rotational Iineshifts of the D fl~X ~ + band convinced the authors of the existence of a perturbing state indicated as a ~fIor ~ state. That would confirm our analysis; we indicate the state as a 3fl one because of the fine structure of the band. The analysis of NaK fluorescence in ref. [2] confirms our assignment. The excited molecular states dissociate to a pair of Na (3 2S) and Cs(5 2D) atoms. Therefore molecular ~,
354.3 322 332.5 336.0 180.2 120 250
8354 8144 8184.3 8180.9 5544.8 5900
1221 [23]
4043 3039 3100
[291
6841 5065 5065 4800 5200 5065.798 4719
[33]
2600
[36]
[24]
[25] [26] [27] 128]
1096 145 250 216 203.1 204 161 291 209.1 544 ~~200 1587
[30] [311 [321 [1] [2) [34] [35] [3] [13] (this work)
dissociation produce atomic fluorescence.is Unfortunatelyshould the cesium 5D—~6P line wavelength equal to 3.6 ~im which is out of our apparatus sensitivity. We observed therefore only the lines correspondingto the fundamental D transitions whose origin can be due to cascade decay. It is important to remark that other Cs or Na lines are absent.
4. Conclusions This work provides the first experimental evidence of a NaCs molecular band that is assigned to the d 3fl~—pa transition. The upper state seems directly excited from the X ~ ~ singlet ground state by the 514.5 nm Ar~laser line, while the fluorescence decay is to the triplet ground state. This is supported by the absence of saturation effect even at very high laser power density, by energy considerations and by analogies with the other alkali molecules. Our analysis permits also an evaluation of the well depth of the triplet ground state. ~
269
Volume 159. number 4.5
PHYSICS LETTERS A
Acknowledgement The authors wish to thank M. Badalassi and M. Tagliaferri for technical assistance. Moreover, one of us (A.K.) wishes to express heartfe]t thanks to the director and to the staff of IFAM CNR in Pisa for the grant and cordial hospitality. The authors are especially grateful to Professor G. Grynberg who kindly provided some alkali-resistant glass samples.
14 October 199!
(IS] Mao-Hong Lu, Wa-Mm Chen and Ci-Ling Pan, App!. Phys. B 48 (1989)365. [16]F.JencandB.A.Brandt,J.Chem.Phys.9l (1989)3287. [17] A.J. Ross, C. Effantin, P. Crozet and E. Boursey, J. Phys. B 23 (1990) L247. [18]U. Diemer. H. Weickenmeier. M. WahI and W. Demtrdder. Chem. Phys. Leti. 104 (1984) 489. [191 D.E. Pritchard, D.C. Burnham and D. Kleppner. Phys. Rev. Lctt. 19 (1967)1363. [20] E.W. Roiheand R.K.B. Helbing,J. Cheni. Phys. 49 (1968) 4750 [211W. Neumann and I-I. Pauly, J. Chem. Phys. 52 (1970) 2548.
References [I] E.J. Breford and F. Engelke. J. Chem. Phys. 71(1979) 1994. [2] D. Eisel. D. Zevgolis and W. Demtroder, J. Chem. Phys. 71 (1979) 2005. [3] A.J. Ross. C. Effantin, J. d’lncan and R.F. Barrow, Mol. Phys. 56 (1985) 903. [41CE. Fellows, J. Verges and C. Amioi, Mo]. Phys. 63 (1988) IllS. [5] CE. Fellows, J. Mol. Spectrosc. 136 (1989) 369. [6]C.E. Fellows. J. Verges and C. Amiot, 1. Chem. Phys. 93 (1990) 6281. [7] H. Kato and H. Kobayashi, J. Chem. Phys. 79 (1983)123. [8] T. Gustavsson, C. Amiot and J. Verges, Chem. Phys. Len. 143 (1 988) 101: Mol. Phys. 64 ( 1988) 279, 293. [9] D. Pavolini. T. Gustavsson, F. Spiegelmann and J.-P. Daudey,J. Phys.B22 (1989) 1721. [I0]J.M. Walter and S. Barrat, Proc. R. Soc. A 119 (1928) 257. [11) W. Weizel and M. KuIp, Ann. Phys. (Leipzig) 4 (1930) 971. 112] R. Beuc, S. Milosevic and 0. Pichler, J. Phys. B 17 (1984) 739 [13]N.TakahashiandH.Kato,J.Chem.Phys.75(198l)4350. [l4)A.Sharma.G.L. Bhale, MAN. Razwi and MN. Dixit, Opt. Commun.61 (1987)21.
270
[221 D.D. Konowalowandj.L. Fish,Chem. Phys. 84(1984)463. [23] I. Schmidi-Mink, W. Muller and W. Meyer, Chcm. Phys. 92 (1985) 263. [241 F. Martin. R. Bacis, J. Verges. C. Linton. 0. Bujin. CII. Cheng and E. Stad, Spectrochim. Acta 44A (1988) 1369. [25] X. Xie and R.W, Field. J. Chem. Phys. 83 (1985) 6193. 1261 D.D. Konowalow, ME. Roscnkrantz and M.L. Olson. -~• Chem. Phys. 72 (1980) 2612. [27] 0.-H. Jeung, J. Phys. B 16 (1983) 4289. [28] L. Li, S.F. Rice and R.W. Field, J. Chem. Phys. 82 (1985) 1178. [29] 0.-H. Jeung and A.J. Ross, J. Phys. B 21(1988)1473. [30] F. Spiegelmann, D. Pavolini and i-P. Daudcy, J. Phys. B 22(1989)2465. [311 0.-H. Jeung. F. Spicgelmann, 3.-P. Daudey and i-P. Malrieu. J. Phys. B 16 (1983) 2659, [321 U. Diemer, J. (iress and W. Demtrbder, Chcm. Phys. Leit. 78 (1991) 330. [33] 1. Schmidt-Mink, W. Muller and W. Meyer, Chem. Phys. Lett. 112 (1984) 120.
[3410.-H.
Jeung, J.P. Daudey and i-P. Malrieu, Chem. Phys. Len. 94 (1983)300. [35] Wi. Stevens, D.D. Konowalow and LB. Ratcliff, J. (Them. Phys.80(l984) 1215. [36]D. Pavolini, T. Gustavsson, F. Spiegelmann and i-P. Daudey.J.Phys.B22(1989) 1721.
PHYSICS LETTERS A
Observation of a new near-red band of the NaCs molecule A. Kopystynska
~,
C. Gabbanini, S. Gozzini, M. Biagini
Islitulo di Fisica .1 tom Ica e Mo/ceo/are del C’onsiglio j’vaionale del/c Ricerche, Via dcl Giardino 7, 56127 Pisa, flu/i’
and L. Moi Dipartimenlo di Fisica, Universitd di Siena, Via Banchi di Sotto 55, 53100 Siena, halt’ Received 21 May 1991 revised manuscript received 7 August 1991 accepted for publication 13 August 1991 Communicated by B. Fricke
A new near-red band of the NaCs molecule has been observed in a cell containing dense sodium and cesium vapors irradiated 3fl—.a ~ electronic transition. by the 514.5 nm Ar laser line. The band is assigned to the d
1. Introduction Although the diatomic alkali metal spectra have been studied since the very beginning ofthis century, some of the heteronuclear molecules are still very littie known and require further study from both the experimental and the theoretical point of view. More precisely, an up to date review shows that the NaK [1—3],NaLi [4—6]and RbCs [7—9]molecules have been extensively investigated while, besides some old experiments [10,111, there are a few papers on KRb and NaRb [12—17].Finally a detailed analysis of the D 2fl—~X‘~ green band of NaCs has been reported by Diemer et al. [18]. The near-red band of the NaCs molecule reported here has been accidentally observed in a cell contaming a mixture of all alkali metals except lithium and a few Torr of a buffer gas, upon 514.5 nm Ar~ laser line excitation. The whole fluorescence spectrum shows atomic lines and molecular bands due to both radiative decay and energy transfer processes. This is due to the presence of ten different diatomic molecules (Na 2, K7, Rb7, Cs2, NaK, NaRb, NaCs, KRb, KCs and RbCs), besides the atoms, in the vaPermanent address: Institute of Experimental Physics, Warsaw University. ul. Hoza 69. 00681 Warsaw, Poland.
266
por mixture. Therefore the identification of the molecule emitting the red band was not straightforward. The task was complicated not only by the poor knowledge of some of these molecules but also by the fact that the relative vapor densities depend in a complex way both on the initial composition of the metal sample and on the temperature. Therefore it was necessary to prepare and examine many cells filled with various combinations of metal pairs and to analyze many molecular spectra.
2. Experimental apparatus and results An Ar~laser beam, tuned to the 514.5 nm line, crosses an alkali-resistant glass cell that is placed in an oven and is heated up to a temperature of 350°C. The fluorescence is analyzed by a very-large-band apparatus consisting of two monochromators, one covering the 400—8 50 nm wavelength range and the other one the 1—2.5 ~im range. Although the observed spectra in the four alkali cells are very rich and complex, all the lines and bands have been assigned with the exception of the band shown tn fig. 1, which is not reported in literature. The band cxtends from 655.5 to 663.3 nm, i.e. for about 180 cm~,and it consists of only five well distinguished
0375-9601/91 /$ 03.50 © 1991 Elsevier Science Publishers B.V. All rights reserved.
Volume 159, number 4,5
PHYSICS LETTERS A
14 October 1991
0
10
20
30
40
50
60
70
1L (Wfcm2)
Fig. 2. Intensity of the line at ~=657.5 nm versus laser power. Solid line represents the linear regression.
~
6500
j~j~I
6550
~
10
3600
6650
Fig. 1. Spectrum of the near-red band of the NaCs molecule observed in the cell containing Na, K, Rb and Cs, T= 320°C, ‘L= 50 W/cm2.
vibrational transitions at wavelengths equal to 655.5, 657.5, 659.5, 661.4 and 663.3 nm respectively. The mean distance between them is about 46 cm~.The band has also a fine structure, as shown in fig. 1. Each vibrational transition has three rotational components with a mean distance between them of about 7 cm~.This is a signature of a fl—~Itransition. The band intensity depends linearly both on the laser power and on the total vapor density, as shown in fig. 2, where the intensity of the maximum of the band at 2=657.5 nm versus laser power is displayed, and in fig. 3, where the intensity variation of the line at A = 655.5 nm versus the inverse of the temperature T of the cell is plotted, It is important to remark that the band excitation requires rather high laser light power and that there
01
1.65
1.75
1.85
1.95 l/T
(10
~2.05 /K)
Fig. 3~Intensity ofthe line at ~=655.5 nm versus l/T.
is no evidence of fluorescence saturation even with 70 W/cm2. Moreover the linear dependence of the fluorescence intensity on laser power, as shown in fig. 2, indicates that the band is not due to a twophoton excitation process. The linear dependence of the fluorescence intensity on 1 / T, as shown in fig. 3, excludesa collisional origin ofthe band. Another important remark to be given is that the other blue-green Ar~laser lines do not excite this band. Cells fitted with all the possible combinations of alkali atoms were tested and the band was found only in the cell containing Na and Cs. The molecular fluorescence is less intense in this cell and it is observed only at high temperatures (T> 300°C). In the cell filled with Na, K, Rb and Cs, on the other hand, the band is still observed at a temperature of 220°C.This different behaviour is probably due to the relative Cs densities which are very different in these two cells. 267
Volume 159, number 4,5
1
PHYSICS LETTERS A
o~2 NaCs
1 010
~
Na
2
1 1013
1014
~~15
1016
n 1017 (Cs)
(cm 1018 3)
Fig. 4. Plot of the calculated molecular densities as a function of Cs atomic density.
The Cs/Na ratio can be significantly changed by just a small variation of the cesium quantity in the metal deposit of the cell. The relative molecular densities are strongly influenced by the atomic ones and in particular the NaCs/Na 2 ratio increases with the Cs/ Na ratio, as shown in fig. 4. The curves reported in this figure have been calculated by using the rate coefficients for molecular formation and by imposing mass conservation. We experimentally measured the relative atomic densities in the two cells by white light absorption and the Cs/Na ratio was effectively larger in the cell containing Na, K, Rb and Cs. We also checked experimentally that the red band does
14 October 1991
plicated by the total absence of theoretical evaluations of the electronic potential curves. Therefore the identification has been derived according to energy considerations and to the Wigner—Witmer correlation rule, which correlates the molecular electronic levels to the atomic ones (table 1). Our conclusions are that the 514.5 nm Ar~laser line excites both the allowed X ‘~ —~D fl transition and the slightly forbidden X ‘~ —~d3fl transition. After the results shown in figs. 2 and 3, it seems, in 3fl state.population The molecules exfact, unlikely to be a collisional transfer cited from to thethese D ifitwo to states the d decay to the ground state by emitting two bands: a red band which corresponds to the d 3[1—3a 3~±transition and a green molecular band, corresponding to the D ifl~x~f transition. This last one, shown in fig. 5, has been reported for the first time by Diemer et al. [18]. The lowest trip-
~ .~
not finally belong webycame toan theelectronic Na2 to the or Cs2 conclusion molecular that spectrum must and be emitted transition of itthe NaCs molecule.
~ 5300
5500
5400
3. Discussion Fig. 5. Fluorescence spectrum ofthe D fl-.X
The identification of the band transition is corn-
~°
NaCs.
Table I NaCs molecular states, atomic excitation energies E,,,~and correlated atomic States. NaCs ~ 3fl, B fl, c A~ b 3fl, D fl e ~, C~ d311, Gil, h ~ F ‘~, g 3~~ H’~,i
268
E ‘A f3~~
E~(cm~)
Cs
Na
011178—11732 14499—14597 16956—16973 18535
6P 6S SD112377 6S312512 7S
3S 3S 3P, 3S 3S 72,312
green band of
Volume 159, number 4,5
PHYSICS LETTERS A
Table 2 Known spectroscopic constants of the alkali molecule a ~ Molecule
14 October 1991
states.
w,
B,
r,
D,
(cm’)
(cm—’)
(A)
(cm—’)
TI’, (cm’)
Ref. theor.
exp.
7Li 2
66.4 63.73 65.17 73.0
6Li 2 Na2
K2 Rb2 Cs2 LiNa NaK
NaRb NaCs RbCs
24.47 23.14 26.37 11 12(11.2) 39.90 22.82 23,1 23 26.9 22.99086 48.48 46 30.67
0.2743 0.2786 0.329
4.068 4.182 4.154 4.13 5.206 5.3
0.00597 5.731 5.338 6.38 0.0597 0.1390 0.0392 0.0395
0.03936956
4.754 5.457 5.431 5.59 5.180 5.438
5.626
let state of the red band should have a very 3~ shallow ground potential curve, as in the case of the a state in all other alkali metal diatomic molecules (see table 2). The wavelength and the extension of the fluorescence band imply that the a ~ state potential curve of the NaCs molecule is about 4000 cm~ above the minimum of the X ~ ground state potential curve and its potential depth is larger than 200 cm This is consistent with the results of Na—Cs scattering experiments in refs. [19—21].The greenband intensity shows saturation by increasing the laser power density, as it should be for an allowed transition, while the other band does not, supporting the hypothesis that it is excited by a forbidden transition. In ref. [18] the analysis of the rotational Iineshifts of the D fl~X ~ + band convinced the authors of the existence of a perturbing state indicated as a ~fIor ~ state. That would confirm our analysis; we indicate the state as a 3fl one because of the fine structure of the band. The analysis of NaK fluorescence in ref. [2] confirms our assignment. The excited molecular states dissociate to a pair of Na (3 2S) and Cs(5 2D) atoms. Therefore molecular ~,
354.3 322 332.5 336.0 180.2 120 250
8354 8144 8184.3 8180.9 5544.8 5900
1221 [23]
4043 3039 3100
[291
6841 5065 5065 4800 5200 5065.798 4719
[33]
2600
[36]
[24]
[25] [26] [27] 128]
1096 145 250 216 203.1 204 161 291 209.1 544 ~~200 1587
[30] [311 [321 [1] [2) [34] [35] [3] [13] (this work)
dissociation produce atomic fluorescence.is Unfortunatelyshould the cesium 5D—~6P line wavelength equal to 3.6 ~im which is out of our apparatus sensitivity. We observed therefore only the lines correspondingto the fundamental D transitions whose origin can be due to cascade decay. It is important to remark that other Cs or Na lines are absent.
4. Conclusions This work provides the first experimental evidence of a NaCs molecular band that is assigned to the d 3fl~—pa transition. The upper state seems directly excited from the X ~ ~ singlet ground state by the 514.5 nm Ar~laser line, while the fluorescence decay is to the triplet ground state. This is supported by the absence of saturation effect even at very high laser power density, by energy considerations and by analogies with the other alkali molecules. Our analysis permits also an evaluation of the well depth of the triplet ground state. ~
269
Volume 159. number 4.5
PHYSICS LETTERS A
Acknowledgement The authors wish to thank M. Badalassi and M. Tagliaferri for technical assistance. Moreover, one of us (A.K.) wishes to express heartfe]t thanks to the director and to the staff of IFAM CNR in Pisa for the grant and cordial hospitality. The authors are especially grateful to Professor G. Grynberg who kindly provided some alkali-resistant glass samples.
14 October 199!
(IS] Mao-Hong Lu, Wa-Mm Chen and Ci-Ling Pan, App!. Phys. B 48 (1989)365. [16]F.JencandB.A.Brandt,J.Chem.Phys.9l (1989)3287. [17] A.J. Ross, C. Effantin, P. Crozet and E. Boursey, J. Phys. B 23 (1990) L247. [18]U. Diemer. H. Weickenmeier. M. WahI and W. Demtrdder. Chem. Phys. Leti. 104 (1984) 489. [191 D.E. Pritchard, D.C. Burnham and D. Kleppner. Phys. Rev. Lctt. 19 (1967)1363. [20] E.W. Roiheand R.K.B. Helbing,J. Cheni. Phys. 49 (1968) 4750 [211W. Neumann and I-I. Pauly, J. Chem. Phys. 52 (1970) 2548.
References [I] E.J. Breford and F. Engelke. J. Chem. Phys. 71(1979) 1994. [2] D. Eisel. D. Zevgolis and W. Demtroder, J. Chem. Phys. 71 (1979) 2005. [3] A.J. Ross. C. Effantin, J. d’lncan and R.F. Barrow, Mol. Phys. 56 (1985) 903. [41CE. Fellows, J. Verges and C. Amioi, Mo]. Phys. 63 (1988) IllS. [5] CE. Fellows, J. Mol. Spectrosc. 136 (1989) 369. [6]C.E. Fellows. J. Verges and C. Amiot, 1. Chem. Phys. 93 (1990) 6281. [7] H. Kato and H. Kobayashi, J. Chem. Phys. 79 (1983)123. [8] T. Gustavsson, C. Amiot and J. Verges, Chem. Phys. Len. 143 (1 988) 101: Mol. Phys. 64 ( 1988) 279, 293. [9] D. Pavolini. T. Gustavsson, F. Spiegelmann and J.-P. Daudey,J. Phys.B22 (1989) 1721. [I0]J.M. Walter and S. Barrat, Proc. R. Soc. A 119 (1928) 257. [11) W. Weizel and M. KuIp, Ann. Phys. (Leipzig) 4 (1930) 971. 112] R. Beuc, S. Milosevic and 0. Pichler, J. Phys. B 17 (1984) 739 [13]N.TakahashiandH.Kato,J.Chem.Phys.75(198l)4350. [l4)A.Sharma.G.L. Bhale, MAN. Razwi and MN. Dixit, Opt. Commun.61 (1987)21.
270
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