Intermultiplet transfers of excited sodium atoms induced by nitrogen moleculesJ. M. Mestdagh, D. Paillard, J. Berlande, J. Cuvellier, and P. de Pujo Citation: The Journal of Chemical Physics 89, 251 (1988); doi: 10.1063/1.455518 View online: http://dx.doi.org/10.1063/1.455518 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/89/1?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Elastic scattering and rotational excitation of nitrogen molecules by sodium atoms J. Chem. Phys. 135, 174301 (2011); 10.1063/1.3653983 Intermultiplet and angular momentum transfers of excited sodium atoms in collisions with molecules. II.Models J. Chem. Phys. 88, 3037 (1988); 10.1063/1.453947 Intermultiplet and angular momentum transfers of excited sodium atoms in collisions with molecules. I.Experiment J. Chem. Phys. 88, 106 (1988); 10.1063/1.454642 Transfer of electronic excitation in collisions of metastable argon atoms with nitrogen molecules. II J. Chem. Phys. 77, 5855 (1982); 10.1063/1.443750 Transfer of electronic excitation in collisions of metastable argon atoms with nitrogen molecules J. Chem. Phys. 70, 3171 (1979); 10.1063/1.437904

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.174.21.5 On: Fri, 19 Dec 2014 22:57:24

Intermultiplet transfers of excited sodium atoms induced by nitrogen molecules

J. M. Mestdagh, D. Paillard, J. Berlande, J. Cuvellier, and P. de Pujo Service de Physique des Atomes et des Surfaces, Centre D"etudes Nuc/eaires de Sac/ay, 91191, Gif-sur-Yvette Cedex, France

(Received 27 December 1987; accepted 25 March 1988)

The predictions ofa mUltiple curve crossing model (MCC) were compared to experimental observations of various intermultiplet transfers in thermal energy Na/N2 collisions. This includes comparisons to the energy dependence and the absolute value of the Na(4D-+5S) cross section that was measured in the experimental section of the present work using a crossed beam apparatus. This also includes comparisons with beam data available in the literature. These last experimental results are not always directly comparable to the calculated cross sections. Deconvolution or simulation procedures are then needed. The general agreement between the MCC calculations and the experimental results is good. In many cases it is much better than a factor 2. The cases or disagreement were discussed carefully, and each of them can be attributable to uncertainties in the experiment or in the procedures of deconvolutions and simulations.

I. INTRODUCTION

Inelastic energy transfers between electronically excited alkali atoms and molecular perturbers have attracted large attention over the past years. Numerous works concentrate on thermal energy collisions of the first excited P doublet, either quenching l

•2 or fine structure transitions/ and on

collisions of Rydberg states.4 In contrast, collisions of alkali atoms having 3 to 4 eV initial electronic energy has received less attention.5 The present investigation is both theoretical and experimental. It focuses on these collisions, for inelastic processes leading to neutral products which involve 3 to 4 e V excited states in both the entrance and the exit channels, i.e., for intermultiplet processes where the alkali atom transfers part of its electronic energy as recoil energy and as internal excitation of the molecular perturber.

Inelastic processes involving alkali atoms, such as quenching and intermultiplet transfers, have often been in­terpreted by an electron jump.5 The valence electron of the alkali transfers on the molecular perturber to form an alka­li + -molecule - ion pair during the collision. So, inelastic scattering occurs because a diabatic ion pair surface crosses, and couples, various diabatic covalent surfaces correlating to the alkali-molecule system.

This simple picture has lead to the multiple curve cross­ing (MCC) model of Bauer-Fisher-Gilmore.6 Originally introduced to treat of the Na(3P)-N2 quenching,6 it has also served to qualitatively rationalize inelastic scattering of more excited Na levels (e.g., Ref. 7). Inelastic collisions are then viewed as many step processes with successive nonadia­batic transitions between curves of a covalent vibronic network describing the alkali-molecule system, and curves of an ion pair network describing the alkali + -molecule -system.

The MCC model seems particularly well adapted to si­tuations where the molecular perturber is a good electron acceptor. For instance, recent MCC calculations prove to be in quantitative agreement with the experiment for the

quenching of Na(3P),8 and the intermultiplet transfers Rb(7S~5D) and Na(4D-+5S)9 induced by 02'

We tum now to alkali-molecule systems where the mol­ecule has a negative electron affinity. We first consider low electronic states of these systems, and then higher excited states.

Detailed ab initio calculations of the low energy adiaba­tic potential surfaces of the Na(3S,3P)-H2 10 system show that unlike in the 2AI state correlating to Na(3S) + H 2, a substantial electron transfer from Na to H2 occurs in the 2 B2 state correlating to Na( 3P) + H 2 • These calculations, and similar one on the Na(3S,3P) + N2 system II lead to the bond-stretching picture of collisional quenching that differs significantly from that given by the electron jump model. However, in both cases, a movement of the valence electron cloud from the alkali towards the molecule is the driving force responsible for the quenching. This can explain why the MCC model leads to qualitatively and quantitatively sat­isfying predictions in a large variety of Na(3P) quenching processes. 1.6

We now consider higher electronic excitations. Recent ab initio calculations on the Cs-H2 system substantiate the picture of the electron jump model at energies near the sec­ond P doublet: a diabatic ion pair surface crosses the excited diabatic covalent surfaces. 12 Although not excluded, de­tailed quantal or semiclassical collision dynamics calcula­tions on these surfaces would be cumbersome and difficult to extend to a wide variety of systems. This motivates for the use of a simpler, and therefore more versatile approach, such as the MCC model cited above, which is based on the elec­tron jump model.

The present investigation examines the use of the MCC model as a tool to predict reliable intermultiplet cross sec­tions in Na(nl, n>4) + N2 collisions where the initial exci­tation ofNa is in the 3 to 4 eV energy range, and where the final level ofNa is also excited. The advantage of the Na-N2 system is to allow comparisons ofMCC predictions to many experimental data of crossed beam quality, either obtained

J. Chem. Phys. 89 (1), 1 July 1988 0021-9606/88/130251-06$02.10 @ 1988 American Institute of Physics 251

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.174.21.5 On: Fri, 19 Dec 2014 22:57:24

252 Mestdagh et al.: Collisions of excited Na atoms with N2

in the experimental part of the present work, or available from the literature. This includes comparisons to the follow­ing:

(i) The absolute cross section of the process

Na(4D) + N 2(X I~g+, v = 0) -Na(5S) + N2,

ll.E = - 1348 cm- I (1)

that is measured in the present work as a function of the collision energy [in Eq. ( 1 ), ll.E is the 5S-4D energy defect].

(ii) Absolute cross sections of a wide variety of inter­multiplet transfers given by

Na(n,l) + N2(X I~g+, v = 0) -Na(n',I') + N2 (2)

that are available from the literature for fixed collision ener­gies. 13,14

(iii) The redistribution of the Na electronic energy as recoil energy in Na( 4D,5S)/N2 collisions,I4

As a complement, the predictions of the MCC model are finally compared to cell measurements of various inelastic transfers in Na(4S, 4P and nS, nD with n;;;'5)-N2 colli­sions.7,15,16

II. THE MULTIPLE CURVE CROSSING MODEL

The MCC model, and the calculation code we use, have been described in detail elsewhere.9 Briefly, the system is assumed to evolve in a grid of potential curves built from covalent states of the Na-N2 system, and ion pair states of the Na + -N2- system, The vibrational constants ofN2 and N2- , and the electron affinity of N2 that are needed to built the grid are taken from Ref. 17.

The covalent curves are assumed to be flat and the ionic curves to be purely Coulombic. This approximation is not believed to significantly affect the present calculations. In­deed, scattering of fairly excited Na atoms is considered here, and the crossing distances where the collisional trans­fers occur are about 4 A or larger. Perturbations caused by the Na + core on the negative molecular ion are expected to be fairly weak at these distances.5

The electronic coupling terms at each crossing between covalent and ion pair curves are calculated using the se­miempirical formula of Hasted and Chongl8 with the pa­rameter values given by Barker l9:

H 12 (Re) =A exp( -B'Re), (3)

where Re is the Na-N2 distance at the crossing point. The values of the parameters A and B in expression (3) are, re­spectively, 25 eV and 1.3344 A -1.19 The electron affinity of N2 is - 1.9 eV,I7 It indirectly appears in the coupling ele­ment calculations since it determines the position of the crossings between the ionic curves and the covalent curves. More elaborate formula such as those given by Olson et al.20

or Los et al.21 cannot be used here to calculate the coupling terms because of the negative electron affinity of N2. As in our earlier work,9 the selection rules linked to the symmetry of the colliding system are included into the coupling terms.

The collision dynamics are treated using classical trajec­tories within the framework of a Monte Carlo method. The probability of non adiabatic transition at each crossing is cal­culated by including in the Landau-Zener formula the cou-

pling terms obtained with expression (3). Each nonadiaba­tic transition of the system is assumed to be independent from each other. This assumption is valid for the intermulti­plet transfers between distant covalent states that are consid­ered here. In contrast, the distance between states relevant to I-mixing processes may be smaller than the coupling terms. This precludes the assumption of independent couplings, and no result will be presented here on I-mixing processes.

III. EXPERIMENTAL TECHNIQUE

The experimental setup used to determine the absolute value of process (I) cross section as a function of the colli­sion energy has been described elsewhere.9,22 Briefly, two supersonic beams are crossed orthogonally and two lasers are allowed to prepare the Na( 4D) via a step excitation. The collision energy is varied by changing the velocity of the molecular perturber. This is done either by changing the temperature of the oven generating the N2 beam, or by seed­ing N2 with He. The cross section of process (1) is deduced from the measurement of the fluorescence light intensities arising from both the initial4D and the final5S levels ofNa, The exact procedure is detailed in Refs. 9 and 22. Let us recall from Ref. 9 that the measured cross section is not purely that of process ( 1). It also contains a contribution of the Na( 4D- 5P) intermultiplet transfer that must be in­cluded in the calculations when comparing experiment and theory. The measured cross section really is

a(4D-5S) + 0.48·a(4D-5P). (4)

The reason is that the final level 5S ofNa is not only populat­ed by process (1), but also by a step process with first a 4D- 5P collisional transfer and then a radiative decay 5P-5S.

Two important points have been checked in the present experiment. Within the experimental uncertainties:

(i) The cross sections stay constant as the internal state of the molecular perturber is varied. This has been checked by generating the same collision energy from various expan­sion conditions of the molecular beam.

(ii) The cross section of process ( 1) is not found sensi­tive to the alignment of the 4d orbital. This has been checked by rotating the direction of polarization of the lasers about the relative velocity vector of N a and N 2 •

IV. RESULTS AND DISCUSSION

A. The Na(40 .... SS) intermultiplet transfer

The absolute value of the cross section for process ( 1 ) is reported in Table I at three collision energies for both the present experiment and the MCC calculations. Of course, the calculated cross sections include the correction given by Eq. (4).

Within the experimental uncertainties, the cross section has a weak energy dependence. This tendency is reproduced by the calculations.

Regarding the absolute values of the cross sections, the calculations agree with the experiment within a factor 2 to 4. According to Olson et al.,20 a factor 2 accuracy is to be ex­pected when their coupling terms can be used in MCC calcu­lations. As said above, the use of less refined semiempirical

J. Chern. Phys., Vol. 89, No.1, 1 July 1988 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.174.21.5 On: Fri, 19 Dec 2014 22:57:24

Mestdagh et 8/.: Collisions of excited Na atoms with N2 253

TABLE I. Absolute values of cross sections for the process Na( 4D) + N,(X Il:,+ , v = 0) -Na(SS) + Nz at different collision ener­gies: experiment and MCC calculations.

Collision Experiment Calculations energy (eV) (Al) (A')

0.15 11 ±6 2.9 0.18 8.5 ±4 3.0 0.28 5 ±3 2.9

formula cannot be avoided here. An agreement within a fac­tor 2 to 4 is thus considered as satisfying.

Interestingly, the cross sections reported in Table I for the Na( 4D-+ 5S) transfer induced by N2 are close to those measured and calculated for O2 in Ref. 9. One would have thought indeed that two molecules of so different electron affinities, a negative value of - 1.9 eV for N2 and a positive one of + 0.44 eV for O2 , would induce intermultiplet mix­ing in a substantially different way. The experiment shows it is not the case, and calculations based on the electron jump model reproduce the observation.

B. Na(n,l ..... n',') intermultlplet transfers

Various cross sections relevant to process (2) have been measured by Desfrancois et al. using a crossed beam experi­ment at a fixed collision energy of 0.06 eV.13 Their results are reported in Table II and are compared to MCC calculations. The experiment of Ref. 13 does not provide absolute cross sections directly. A normalization ofthe 4P-+3D cross sec­tion is done to the value of 19 ± 3 A 2 measured in a cell.7 A more recent work suggests a value of 33 ± 8 A 2 for this nor­malization.23 Whatever the normalization, the experimental results confirm the MCC predictions within a factor 2 or better, except for the 4D-+ 5S transfer, where the cross sec­tion of Ref. 13 is small compared to both our calculations and our measurements (compare Tables I and II). This cross section has been measured again by the same group. The new value is an upper limit of 4 A 2, which is more consis­tent with our results.23

Jamieson et al. 14 have also provided crossed beam infor­mation on process (2) cross sections. They have compared in relative values, the magnitude of differential cross sections of various intermultiplet processes at a O' scattering angle, to the magnitude ofthe Na(3P .... 3S) quenching cross section. They consider that the magnitude of these O' differential cross sections well characterizes that of the corresponding total cross sections. Therefore, the data of Jamieson et al. 14

TABLE II. Comparison of the present MCC calculations to the crossed beam data of Ref. 13 for intermultiplet transfer cross sections in Na-Nl

collisions at a 0.06 eV collision energy.

Experiment (Ref. 13) Calculations Transfers (Az) (Al)

4D-5S <1 1.9 4D-3D 22 ± 3 25 4P-3D 19± 8 17

can be related to an absolute scale and absolute cross sections for process (2) can be obtained by normalizing the 3P-+3S quenching cross section to the value 20 A 2 available from the literature. I The corresponding results and our MCC calcula­tions are shown in Table III. The experiments compare with the calculations within a factor 2, except for the 4D-+ 3D and 4P .... 4S transfers. To discuss the last point, it is worth recall­ing that in addition to the question of normalization, the experiment does not provide direct cross section measure­ments. A deconvolution is needed to extract cross section informations from Na recoil energies that are the measured quantities. This procedure is accurate for intermultiplet transfers associated to large recoil energies, but inaccuracies seem difficult to avoid when the recoil energy is small, be­cause many different intermultiplet transfers then contrib­ute to the signal. This can be the case with the 4D .... 3D and

O 2 4P-+4S transfers. In particular, the large value of 144 A given for the 4D-+3D transfer at a 0.16 eV collision energy seems to be at odds with the determination of Ref. 13: 22 ± 3 A2 at 0.06 eV. An increase of more than a factor 6 of this cross section over the range 0.06-0.16 eV is indeed unlikely for an exothermic process. Although no other experimental result is available to confirm the statement, we also believe that the value of 52 A2 for the 4P .... 4S transfer is overesti­mated. The 4P-+4S cross section is indeed even more diffi­cult to extract from the recoil energy measurements than the 4D-+ 3D cross section.

c. Na recoil energy in Na(4D,5S)-N2 scattering

Jamieson et al. 14 have measured the recoil energy distri­bution of Na in collision with N 2 , as function of the Na scattering angle, in an experiment where Na is laser excited to the 4D or 5S levels. Because these levels radiatively decay to lower ones, the Na atoms are before the collision in a superposition of excited levels that Jamieson et al. have esti­mated for the 4D laser excitation. We extended this estima­tion for the 5S laser excitation. The result is, however, more tentative than for the 4D excitation because optical pumping phenomena that are difficult to take into account are expect­ed to playa significant role in this case. Anyway, the mea­sured signals appear as fairly well known superpositions of recoil energy distributions associated to the scattering of Na( 4D, 5S, 4P, 3D, and 4S) by N 2 • The contribution of Na(3P) scattering to the measured signals does not appear

TABLE III. Cross sections of various intermultiplet transfers in Na-Nl

collisions at 0.16 e V. The beam data are deduced from Ref. 14 as explained in the text. fl.E is the energy defect in each process.

Experiment Calculations Transfers (Al) (Al) fl.E(cm- l

)

4D-3P 24± 12 16 - 17593 5S-3P 14±7 19 - 16245 4P-3P 34± 17 22 - 13311 4D-4S 3 - 8 809 4S-3P 48±24 31 - 8 784 5S-4S 1O± 5 10 -7461 4D-3D 144± 72 21 - 5 376 4P-4S 52 ±26 4 -4527

J. Chern. Phys., Vol. 89. No.1, 1 July 1988 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.174.21.5 On: Fri, 19 Dec 2014 22:57:24

254 Mestdagh et al.: Collisions of excited Na atoms with N2

because it has been estimated in the work of Jamieson et al. and has been subtracted. Their data are shown in Figs. 1 and 2 for the 4D and 5S excitations, respectively. The collision energy is 0.16 e V and the scattering angle is O· in the center of mass reference frame.

We have simulated these experimental data by: (i) using the MCC model to calculate the total cross sections associat­ed to the intermultiplet transfers of the 4D, 5S, 4P, and 4S levels towards all possible states of the Na-N2 system that contribute to the measured signal, (ii) doing the proper combination of these cross sections to get the recoil energy spectra, and (iii) convoluting them by a 0.1 eV half-width window function to simulate the experimental recoil energy resolution.

The results are plotted in Figs. 1 and 2, in arbitrary units because the experiment does not provide the absolute value of the signals. One might be surprised of comparing total cross sections calculations to differential cross sections mea­surements at zero scattering angles. This is justified because the experiment has revealed a sharp forward peaked angular distribution, and similar recoil energy distributions for scat­tering at 0·,90·, and 180· angles.

A good agreement is observed between experimental and calculated recoil spectra when the 4D level ofNa is excit­ed (Fig. 1). When the 5S level is excited, the experiment is reproduced within a factor 2 (Fig. 2), but we have seen above that the simulation of the experimental results is more tentative in this case.

Once more, the MCC calculations prove to be fairly ac­curate in predicting cross sections of intermultiplet energy transfers in Na(n,l) + N2 collisions.

As a subsidiary result, the present MCC calculations give insight into the collision dynamics. For instance, Fig. 3

~ 'c ::> .c ~ c 0

"fi '" In II> II> e u

0.5

o 4 Center of Mass Recoil Energy of Na (eV)

5

FIG. 1. Recoil energy distribution in excited Na/N2 collisions at 0.16 eV, when the Na atoms are laser excited to the 4D level. The dots are the experi­mental results of Ref. 14 for a zero scattering angle of Na in the center of mass reference frame. The solid curve is a simulation of the experiment us­ing the present MCC calculations (see the text).

:w c

::>

.e ~ c 0,5 0 .~

CD In II> II> E! u

o 5 Center of Mass Recoil Energy of Na (eV)

FIG. 2. Same as Fig. I when the Na atoms are laser excited to the SS level.

shows the opacity function for the Na(5S) quenching at a 0.2 eV collision energy. It behaves as in an absorbing sphere model, with an absorbing radius of 5 A. This distance corre­sponds to the crossing between the entrance covalent curve Na(5S) + N2 (v = 0) and the first curve (v- = 0) of the Na + -N2- ion pair. A similar behavior is found for the quenching of the other states of Na in the range of 4 eV electronic excitation. The present MCC calculations show also that the fraction ofNa electronic energy transferred as recoil energy depends substantially on the particular inter­multiplet transfer under consideration. For instance, at a collision energy of 0.2 eV, the cross section 4D- 3P is maxi­mum when the recoil energy is 20% of the total electronic energy. The rest of the available energy is then found as vi­brational excitation ofN2. The percentage of recoil energy is

1.0 .1

0.8

~ 0.6 I-

::J iii .:( al 0

0.4 0:: a..

0.2

1 I 1

o 2 3 4 5 6

IMPACT PARAMETER (Al

FIG. 3. Probability of the Na(SS) depopulation by N2 (v = 0) calculated for a collision energy of 0.2 eV and a molecular orientation of 4So.

J. Chern. Phys., Vol. 89, NO.1, 1 July 1988 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.174.21.5 On: Fri, 19 Dec 2014 22:57:24

Mestdagh et al.: Collisions of excited Na atoms with N2 255

TABLE IV. Quenching [part (a) 1 and intermultiplet transfer [part (b) 1 cross sections in excited Na-N2 collisions. Comparison of cell results at a tempera-ture T to the present MCC calculations at a collision energy of 0.06 eV. Ec is the averaged relative energy of Na-N2 in the cell. The word "manifold" means "all the n,l states with n fixed and I> 2" (see Ref. 7).

Initial state Cell experiments of sodium (a) Present

or transfers (b) T('C) Ec(eV) Refs. U(A2) calculations

(a) 4S 225 0.065 270 0.071

5S 6S 7S 8S

5D ISO 0.054

"manifold" 6D

"manifold" 7D

"manifold" 4P 155 0.056

(b) 4P~3D

5S~4P 155 0.056 5S~3D

about 30% for the transfers 4D~ 4S and 4D~ 3D, and 60% for the 4D~4P transfer. It is interesting to recall that about 50% of the N a (3P) electronic energy is transferred as recoil energy when N a (3P) is quenched by N2 .2

D. Comparison with cell measurements

Cell measurements of process (2) cross sections for dif­ferent values of n and I are listed in Table IV. 7,15,16 A com­parison to MCC calculations would require us to average the calculated cross sections over the Maxwellian velocity distri­bution in the cell. However, the slow tail of this distribution corresponds to small collision energies where the Landau­Zener treatment used in the MCC calculations might not be valid. The calculations reported in Table IV thus correspond to a fixed energy of 0.06 eV, which is close to the average collision energy in the cell. Here again, the calculated cross sections compare with the experiment within a factor 2.

V. CONCLUSIONS

The predictions of an MCC model have been compared to experimental observations of various intermultiplet trans­fers in Na(4S, 4P, 5S, and 4D)/N2 thermal collisions. The general agreement between the calculations and the experi­ments is good. The accuracy of the MCC model is often better than a factor 2, and when a disagreement was found, it was attributable to uncertainties in the experiment or, in cases where the comparison between calculations and ex­periments was not direct, to unaccuracies in the simulation and deconvolution procedures of the experimental data.

These encouraging comparisons allow us to speculate that the scope of the MCC model regarding the alkali elec­tronic energy in alkali-molecule inelastic collisions could be 3 to 4 eV. Above 4 eV, we do not expect the MCC model to remain accurate because the various nonadiabatic transfers

15 116±8 107 105 ± 10 86± 8 94 84± 8 99 82 ±9 107 91 ±8 79

16 43±7 71

36 ± 8 68

32 ± 7 71

7 43±4 65 19±3 17

7 32 ± 8 19 1O± 2 19

at each crossing can no longer be treated as independent from each other. Still considering simple theoretical models, the impact approximation model of Petitjean et al.24 for in­stance, would then become a better approach. Below 3 eV, the right approach is certainly the bond-stretched model.

Finally, the MCC calculations provide insight into the collision dynamics. For instance, the quenching ofNa, excit­ed in the 4 e V range, appears as well described by an absorb­ing sphere model. Interestingly also, the amount of energy redistributed as recoil of the products in intermultiplet mix­ing processes (4D-- 3P for example) often differs signifi­cantly from the 50% usually found in the quenching of Na(3P).

ACKNOWLEDGMENTS

We thank A. Binet and P. Meynadier for their help in the experimental part of this work.

'w. H. Breckenridge and H. Umemoto, in Dynamics of the Excited State, Advances in Chemical Physics, edited by K. P. Lawley (Wiley, Chichester, 1982), Vol. L, p. 325.

21. V. Hertel in Dynamics of the Excited State, Advances in Chemical Phys­ics, edited by K. P.Lawley (Wiley, Chichester, 1982), Vol. L, p. 475.

3J. M. Mestdagh, in Electronic and Atomic Collisions, edited by D. C. Lor­ents, W. E. Meyerhof, and J. R. Peterson (Elsevier, Amsterdam, 1986), p. 507.

4F. Gounand and J. Berlande, in Rydberg States of Atoms and Molecules, edited by R. F. Stebbings and F. B. Dunning (Cambridge University, New York, 1983), Chap. 7, p. 229.

'J. P. Schermann, J. P. Astruc, C. Desfrancois, and R. Barbe, in Photoin­duced Electron Transfer, edited by M. A. Fox and M. Chanon (Elsevier, Amsterdam, 1987).

6E. Bauer, E. R. Fisher, and F. R. Gilmore, J. Chern. Phys. 51, 4173 (1969).

7T. F. Gallagher, W. E. Cooke, and S. A. Edelstein, Pbys. Rev. A 17,125 (1978).

J. Chem. Phys., Vol. 89, No.1, 1 July 1988 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.174.21.5 On: Fri, 19 Dec 2014 22:57:24

256 Mestdagh et al.: Collisions of excited Na atoms with N2

"Ch. Desfrancois, J. P. Astruc, R. Barbe, A. Lagreze, and J. P. Scherrnann, Laser Chern. 1, 1 (1986).

9D. Paillard, J. M. Mestdagh, J. Cuvellier, P. de Pujo, and J. Berlande, J. Chern. Phys. 87, 2084 (1987).

lOp. Botschwina, W. Meyer, I. V. Hertel, and W. Reiland, J. Chern. Phys. 75,5438 (1981).

lip. Habitz, Chern. Phys. 54,131 (1980). 12p. X. Gadea, F. Spiegelrnann, M. Pelissier, and J. P. Malrieu, J. Chern.

Phys. 84, 4872 (1986). 13Ch. Desfrancois, J. P. Astruc, R. Barbe, and J. P. Schermann, J. Phys. B

19, L793 (1986). 14G. Jamieson, W. Reiland, C. P. Schulz, H. U. Tittes, and I. V. Hertel, J.

Chern. Phys. 81, 5805 (1984). I5J. P. Astruc, R. Barbe, Ch. Desfrancois, A. Lagreze, and J. P. Scherrnann,

Opt. Cornrnun. 57,175 (1986). 16L. M. Humphrey, T. F. Gallagher, W. E. Cooke, and S. A. Edelstein,

Phys. Rev. A 18, 1383 (1978). 17K. P. Hubert and G. Herzberg, Molecular Spectra and Molecular Struc­

ture. IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York,1979).

'"J. B. Hasted and A. Y. J. Chong, Proc. Phys. Soc. 80, 441 (1962). 19J. R. Barker, Chern. Phys. 18,175 (1976). 2°R. E. Olson, P. T. Smith, and E. Bauer, Appl. Opt. 10, 1848 (1971). 21J. Los and A. W. Kleyn, in Alkali Halide Vapors, edited by P. Davidovits

and D. L. McPadden (Academic, New York, 1979), Chap. 8, p. 275. 22J. Cuvellier, L. Petitjean, J. M. Mestdagh, D. Paillard, P. de Pujo, and J.

Berlande, J. Chern. Phys. 84,1451 (1986). 23J. P. Astruc, Ch. Desfrancois, R. Barbe, and J. P. Schermann, J. Chern.

Phys.88, 106 (1987). 24p. Gounandand L. Petitjean, Phys. Rev. A 30, 61 (1984); L. Petitjean, F.

Gounand, and P. R. Pournier, ibid. 30, 71 (1984); 30, 736 (1984), L. Petitjean and P. Gounand, ibid. 30, 2946 ( 1984).

J. Chem. Phys., Vol. 89, No.1, 1 July 1988 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.174.21.5 On: Fri, 19 Dec 2014 22:57:24