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Effects of perturbations on the term values, Landé factors of B0u+ and A1u states and on intensities of B0u+-X1g transitions of 130Te2
Volume 166, number 3
EFFECTS OF PERTURBATIONS
CHEMICAL PHYSICS LETTERS
ON THE TERM VALUES, LAND6
23 February 1990
FACTORS
OF BO,’ AND Al, STATES AND ON INTENSITIES OF BO:-Xl, TRANSITIONS OF ‘qe,
A.V. STOLYAROV, E.A. PAZYUK, L.A. KUZNETSOVA The Laboratory ofLaser Spectroscopy, Department of Chemistry, Moscow M. Lomonosov State University, 119899 Moscow, USSR
Ya.A. HARYA and R.S. FERBER The Laboratory of Spectroscopy, P. Stuchka Latvian State University,226098 Riga, Latvia, USSR Received 12 August 1989; in final form 12 December I989
Measurements by the Hanle effect of the Land6 factors in the BO: and A 1u states of 130Te2have been performed for several rovibronic levels. The rotational intensity distribution within fluorescence series in the spectra of laser-excited Tez has been studied. Experimentally observable perturbations in the term value positions, g factors and in the intensity distribution have been interpreted as the heterogeneous electronic-rotational interaction between BO: and Al, states.
1. Introduction Tez is one of the diatomic homonuclear molecules which has been investigated extensively [ l-121. As well as the I2 molecule, it has become a test molecule for the practical and theoretical approaches of diatomic spectroscopists. This work deals with the interpretation of the perturbations observed in the energetic, radiation and magnetic characteristics of 13’Te2, which have been observed in the present and in earlier work [ 2-7,10,12]. It has been experimentally established that there are: (a) irregular shifts of the rovibronic level positions of BO: and Al, states in the absorption and laser-induced fluorescence (LIF) spectra [ 2-71; (b) features of the rotational intensity distribution within LIF series of the BO: -Xl, transition [ 3,6,12]; (c) significant changes (up to the sign) of Land6 factors for some rovibronic levels of the diamagnetic BO: state [10,12]. Analogous perturbations have been studied by GouCdard and Lehmann [ 13,141 in *OSezand have been explained as heterogeneous electronic-rotational interaction [ 15 1. We will try to interpret all effects mentioned above for ‘30Tez in terms of the same interaction, taking into account that electronic states of Te, should be represented as wavefunctions of Hund’s case “c” type.
2. Experimental
results
The experimental methods and apparatus applied to measure g factors from the Hanle effect and relative intensities of rotational lines have been described previously [9,10]. We note that fixed-frequency Ar+ and 290
Volume 166,number 3
CHEMICALPHYSICSLETTERS
23 February 1990
He-Ne laser lines ranging from 441.6 to 496.5 nm have been used, so only a limited number of rovibronic levels of the BO: and Al Ustates have been excited [ 2,6,7,9,10]. The experimental results are given in tables 1 and 2; their accuracy is 1%20%.
3. The term values and molecular constants For the states considered the rotational Hamiltonian has a nondiagonal part HP,,.,= -2&l-J, [ 161, which couples the various states with AQ=Rf 1. The matrix elements of the perturbation operator are (nv~~lH,,)mv’~~lJ)=-P(B)[(JTSZ)(J~52+1)]”2,
(1)
where P(B) is defined by P(B)=~(U~B~U’),
~={rqJ,,
ImQkl),
J,=L+s.
(2)
Using this model the experimental term values of the BOZ and Al, states were fitted by the nonlinear leastsquares procedure [ 151. Molecular constants for both states and the coupling constant r,+’ were chosen as adjustable parameters. Table 1 The mixing coefficients,
experimental
107 179 243 197 99 251 103 137 95
Table 2 The experimental
and calculated
Q-branch
2 3 4 5 7 8 9 10 12 13
I8 30 30 15 4 13 11 2 7 8
and calculated
Landt factors for rovibronic
0.55 0.46 0.97 0.99 0.99 0.95 0.89 0.97 0.99
0.83 0.89 0.24 0.14 0.14 0.31 0.46 0.25 0.14
values of relative intensities:
levels of 90:
45 90 100 61 5 35 41 13 16 27
-1.60
- 2.00 - 1.15 0.36 0.16 0.15 -0.30 -0.23 - 0.40 0.30
u= 5, J= 103,90:-X1,
P-branch
17 30 30 16 4 13 11 3 6 7
and A 1: mixed states
-0.86 0.33 * 0.20 0.14 -0.32 -0.25 -0.43 0.31
transition R-branch
8 15 15 8 2 6 6 1 3 4
50 100 113 75 5 40 47 20 15 27
4 7 11 13
8 15 15 15
3 5 8 10
3 6 5
6 6 1
2 5 5
4
4
2
291
Volume 166, number 3
The vibrational equation
CHEMICAL PHYSICS LETTERS
basis wavefunctions
I vJ) have been found by numerical
23 February 1990
solution of the radial SchrGdinger
[d2/dR2+E,(R)+BJ(J+l)]IuJ)=E,,Iu,),
(3)
where En(R) is the potential which has been constructed by the RKR procedure [ 171 with adjustable molecular constants. The term values were deduced from the transitions observed in the LIF series by using molecular constants for the X0: and X 1, states and wavelengths of the laser-exciting lines with accuracy E 0.0 1 cm-’ [ 61, Calculated sets of parameters are listed in table 3. Some mixing coefficients of basis wavefunctions for interacting rovibronic levels are given in table 1. The molecular constants for the BO: state are comparable with the values deduced from the abc,?rption spectra [ 11, but there are essential distinctions between the calculated and previously known const nts for the Al, state [ 51. The value of the adjustable parar. ::ter tl“p is 1_220.2. It is interesting to compare it to the value qtheorfor an idealized case for which J, car- be associated with the quantized value J,(J,+ 1) [ 161. In this case and for the interacting states BO: and Al, we have ?liheor=fi. 4‘h”“‘=[(J*+SZ)(Ja-~+l)]“2 We note that deperturbed vibrational terms for v=O levels of the BO: and Al, states are approximately equal, So the difference between perturbed and deperturbed terms is almost the J-independent value AT,= P2 (B) / [&( BO: ) -I?,-,( Al,) 1. Therefore in this case the experimentally observed rovibronic levels of the BO: and Al, states can be expressed as a Dunham expansion with deperturbed rotational constants and the shift of the vibronic terms will equal AT, [6].
4. The Land6 factors Taking into account the Hamiltonian presented as follows:
considered
above, the g factors for the BO: and Al:
states can be
1) >
g<,,,m)ti=T 2CoC, Gp (W;>I,/%=&C:G,IJ(J+
(4)
where Co, C, are the mixing coefficients and G_ and G, are the corresponding electronic matrix elements If the interaction is not so strong and the explicit form of the mixing coefficients is used, we obtain ~~,,,,,=~G-v(~JI
>
l/R’ly;)(~~lG)/~,,
[ 141.
(5)
where A,, is the difference between deperturbed rovibronic terms of interacting levels. Taking the value G_ = 2~ and the mixing coefficients obtained from the term values, the g factors for the rovibronic levels of BO,f and A 1: mixed states have been calculated (see eqs. (4) and ( 5) ). These values and experimental g factors are presented in table 1.
Table 3 The deperturbed molecular constants (cm-‘) of BO: and Al, states of 13’Te2a)
T, W W& WY. B, a.
BO: state
Al, state
22203.5( 1.6) 163.5( 1.2) 0.563(0.045) -0.042(0.009) 32.58(0.04)x 1O-3 1.35(0.05)X 1o-4
22209.2(1.9) 155.9( 1.3) 2.57(0.24) 0.053 (0.010) 32.16(0.03)xlO-’ 2.17(0.07)xW4
a) The values in parentheses are twice the standard deviation.
292
CHEMICAL PHYSICSLETTERS
Volume 166, number 3
23February1990
So only states of the same parity and nuclear statistics would be mixed by the magnetic field. For the Al; state the g factor is g,= -G,/.J(.J+ 1). The experimental value of the g factor for v=2, J=96 of the A I ; state is - 2 x 10m4,therefore G.=2. Consequently, this g factor can be expressed as -2/J(J+ 1). This equation is equal to the theoretical one for the LandC factors for the F2 component of a 3C; state [ 131.
5. Intensity distributions in the BOG-Xl, transition For interacting BO: and A 1: states the matrix element of the electric dipole operator for the BO: -X 1, transition is
~~*I~l~~g~=~~OI~~OU+-x,,I+~,ICIAI”-XI~Il 9
(6)
where
~n*)=CoIBO:)+C,
IAl:),
(7a)
d,=d,,+_,,,=Re,o:_,,,(R~~~:;J”)(v,Ivl;.,>cr(J,~,~=-1).
(7b)
d,, =&WI.- -ReA,._x,,(R~~JJ”)(v;Iv[;“)cy(JI,~,A8=O).
(7c)
Here, Re( R ;JJ”) denotes the dependence of the electronic dipole transition moment on the Rsp and IYare direction cosine matrix elements [ 191. Finally, relative rotational line intensities within a given band are
centroid [ 181
Ip/l~=(vp/v~)3[(J’+2)/(5’-l)][1+~J2J’lo]*/[1-~J2olJ1]*,
@a)
I,/Io=(vp/yo)3[(J’+2)/(25’+1)][1+X~~]*/[1-XJ2ISo]2,
(8b)
I,/I~=(v,/v~)3[(I’-1)/(25’+1)][1-~~~]~/[1-~J2/so]~,
(8~)
where x= (G/Co)(Re~~,x,,
lRe,,:-,,,)((v;Ivl;~>/(v,IV[;-
>) s
(9)
The perturbation model has been used for interpretation of the relative intensities of LIF spectra in the BO:-Xl, transition from v=O, J= 179; V= 1, J=243; v=3, J=251; ~5, J= 103; ~5, J= 137 of 130Te2which have been measured [ 6,121. The experimental and calculated (for nonperturbed and perturbed approximations) relative line intensities for one of the progressions (v=5, J= 103) are given in table 2. As can be seen, the perturbation model improved the agreement with the experimental data. It is clear (see eq. (9 ) ) that the intensity distribution depends on the degree of mixing of the interacting states (C, /Co) and on the relative probabilities of the vibronic transitions. Obviously, perturbations in the intensity distribution are more pronounced in a “weak” transition, when it is mixed with a “strong” transition. It is interesting to note that for Q-branch lines the intensity distribution is determined by the value [ l(Cl/Co) (d,,/d, )dm]*, which is equal to 1 for experimentally observed transitions (J’ > 100) [6,12]. Thus the Q-branch line intensities have been used to obtain the deperturbed dependence of the transition moment on the R-centroid for the BO:-Xl, system: Re,,o:_x,,(R$J”) =0.907- 1.36(RsJ” -5.156). On the contrary, the R- and P-branch line intensities in such mixed transitions permit us to calculate the value and sign of the ratio d,,/d,. For a BO: -Xl, transition the ratio of the parallel and perpendicular transition moments has been found to equal 202 5.
293
Volume 166, number 3
CHEMICAL PHYSICS LETTERS
23 February 1990
6. Conclusion We note that the perturbation model allowed us to fit energetic, magnetic and radiation characteristics of the BOZ and A I u states in a unified way. But taking into account the small number of the experimental points, this model should not be assumed to be absolutely correct. The Land6 factors and rotational distribution of the intensity are very sensitive to small perturbations of the molecular states. So the perturbation model can be improved by systematic and accurate measurements of these “‘Te2). In particular, these results may parameters (in dependency on v and J) for different isotopes ( ‘Te2, throw some light upon the nature and molecular constants of the poorly examined excited 1, state that lies near in energy to the states considered [ 61.
Acknowledgement The authors wish to thank 1-P. Klinzare and Dr. M.Ya. Tamanis for assistance with the experiments reported here and for providing unpublished results of the Land6 factor measurements.
References [ 1] R.F. Barrow and R.P. du Parcq, Pmt. Roy. Sot. A 327 ( 1972) 279. [ 21 K.K. Yee and R.F. Barrow, J. Chem. Sot. Faraday Trans. II 68 ( 1972) 1397. [ 31 T.J. Stone and R.F. Barrow, Can. J. Phys. 53 (1975) 1976. 141J. Verg&, J. d’lncan, C. Effantin, D.J. Greenwood and R.F. Barrow, J. Phys. B 12 ( 1979) L301. [ 51 C. Effantin, J. d’Incan, J. Vergks, M.T. Macpherson and R.F. Barrow, Chem. Phys. Letters 70 ( 1980) 560. [ 61 J. Verg&, C. Effantin, 0. Babaky, J. d’lncan, S.J. Presser and R.F. Barrow, Physica Scripta 25 ( 1982) 338. [ 71 A. Topuzkhanian, 0. Babaky, J. VergBs,R. Willers and B. Wellegehausen, J. Mol. Spectry. I 13 ( 1985) 39. [ 81 K. Balasubramanian and Ch. Ravimohan, J. Mol. Spectry. 126 ( 1987) 220. [ 91 Ya.A. Harya, R.S. Ferber, N.E. Kuz’menko, O.A. Shmit and A.V. Stolyamv, J. Mol. Spectry. 125 (1987) 1. [lo] R.S. Ferber, O.A. Shmit and M.Ya. Tamanis, Chem. Phys. Letters 92 [ 1982) 393. [ 111R.S. Ferber and M.Ya. Tamanis, Chem. Phys. Letters 98 (1983) 577. [ 121Radiacionnie i stolknovitelnie charakteristiki atomov i molekul. Tellur [Radiation and collision characteristics of atoms and molecules. Tellur] Latvia P. Stuchka State University, Riga ( 1989), in Russian. [ 131G. Gouedard and J.C. Lehmann, J. Phys. B 9 (( 1976) 2113. [ 141G. Gouddard and J.C. Lehmann, Faraday Discussions Chem. Sot. 71 ( 1981) 143. [ 15] H. Lefebvre-Brion and R.W. Field, Perturbations in the spectra of diatomic molecules (Academic Press, New York, 1986). [ 161L. Veseth, J. Phys. B 6 (1973) 1473. [ 171R.N. Zare, A.L. Schmeltekopf, W.J. Harropand D.L. Albritton, J. Mol. Spectra.46 (1973) 37. [ 181A. Fraser, Can. J. Phys. 32 ( 1954) 5 15. [ 191J.T. Hougen, The calculations of rotational energy levels and rotational line intensities in diatomic molecules, NBS Monograph I 1S (Nat]. Bur. Std., Washington, 1970).
294
EFFECTS OF PERTURBATIONS
CHEMICAL PHYSICS LETTERS
ON THE TERM VALUES, LAND6
23 February 1990
FACTORS
OF BO,’ AND Al, STATES AND ON INTENSITIES OF BO:-Xl, TRANSITIONS OF ‘qe,
A.V. STOLYAROV, E.A. PAZYUK, L.A. KUZNETSOVA The Laboratory ofLaser Spectroscopy, Department of Chemistry, Moscow M. Lomonosov State University, 119899 Moscow, USSR
Ya.A. HARYA and R.S. FERBER The Laboratory of Spectroscopy, P. Stuchka Latvian State University,226098 Riga, Latvia, USSR Received 12 August 1989; in final form 12 December I989
Measurements by the Hanle effect of the Land6 factors in the BO: and A 1u states of 130Te2have been performed for several rovibronic levels. The rotational intensity distribution within fluorescence series in the spectra of laser-excited Tez has been studied. Experimentally observable perturbations in the term value positions, g factors and in the intensity distribution have been interpreted as the heterogeneous electronic-rotational interaction between BO: and Al, states.
1. Introduction Tez is one of the diatomic homonuclear molecules which has been investigated extensively [ l-121. As well as the I2 molecule, it has become a test molecule for the practical and theoretical approaches of diatomic spectroscopists. This work deals with the interpretation of the perturbations observed in the energetic, radiation and magnetic characteristics of 13’Te2, which have been observed in the present and in earlier work [ 2-7,10,12]. It has been experimentally established that there are: (a) irregular shifts of the rovibronic level positions of BO: and Al, states in the absorption and laser-induced fluorescence (LIF) spectra [ 2-71; (b) features of the rotational intensity distribution within LIF series of the BO: -Xl, transition [ 3,6,12]; (c) significant changes (up to the sign) of Land6 factors for some rovibronic levels of the diamagnetic BO: state [10,12]. Analogous perturbations have been studied by GouCdard and Lehmann [ 13,141 in *OSezand have been explained as heterogeneous electronic-rotational interaction [ 15 1. We will try to interpret all effects mentioned above for ‘30Tez in terms of the same interaction, taking into account that electronic states of Te, should be represented as wavefunctions of Hund’s case “c” type.
2. Experimental
results
The experimental methods and apparatus applied to measure g factors from the Hanle effect and relative intensities of rotational lines have been described previously [9,10]. We note that fixed-frequency Ar+ and 290
Volume 166,number 3
CHEMICALPHYSICSLETTERS
23 February 1990
He-Ne laser lines ranging from 441.6 to 496.5 nm have been used, so only a limited number of rovibronic levels of the BO: and Al Ustates have been excited [ 2,6,7,9,10]. The experimental results are given in tables 1 and 2; their accuracy is 1%20%.
3. The term values and molecular constants For the states considered the rotational Hamiltonian has a nondiagonal part HP,,.,= -2&l-J, [ 161, which couples the various states with AQ=Rf 1. The matrix elements of the perturbation operator are (nv~~lH,,)mv’~~lJ)=-P(B)[(JTSZ)(J~52+1)]”2,
(1)
where P(B) is defined by P(B)=~(U~B~U’),
~={rqJ,,
ImQkl),
J,=L+s.
(2)
Using this model the experimental term values of the BOZ and Al, states were fitted by the nonlinear leastsquares procedure [ 151. Molecular constants for both states and the coupling constant r,+’ were chosen as adjustable parameters. Table 1 The mixing coefficients,
experimental
107 179 243 197 99 251 103 137 95
Table 2 The experimental
and calculated
Q-branch
2 3 4 5 7 8 9 10 12 13
I8 30 30 15 4 13 11 2 7 8
and calculated
Landt factors for rovibronic
0.55 0.46 0.97 0.99 0.99 0.95 0.89 0.97 0.99
0.83 0.89 0.24 0.14 0.14 0.31 0.46 0.25 0.14
values of relative intensities:
levels of 90:
45 90 100 61 5 35 41 13 16 27
-1.60
- 2.00 - 1.15 0.36 0.16 0.15 -0.30 -0.23 - 0.40 0.30
u= 5, J= 103,90:-X1,
P-branch
17 30 30 16 4 13 11 3 6 7
and A 1: mixed states
-0.86 0.33 * 0.20 0.14 -0.32 -0.25 -0.43 0.31
transition R-branch
8 15 15 8 2 6 6 1 3 4
50 100 113 75 5 40 47 20 15 27
4 7 11 13
8 15 15 15
3 5 8 10
3 6 5
6 6 1
2 5 5
4
4
2
291
Volume 166, number 3
The vibrational equation
CHEMICAL PHYSICS LETTERS
basis wavefunctions
I vJ) have been found by numerical
23 February 1990
solution of the radial SchrGdinger
[d2/dR2+E,(R)+BJ(J+l)]IuJ)=E,,Iu,),
(3)
where En(R) is the potential which has been constructed by the RKR procedure [ 171 with adjustable molecular constants. The term values were deduced from the transitions observed in the LIF series by using molecular constants for the X0: and X 1, states and wavelengths of the laser-exciting lines with accuracy E 0.0 1 cm-’ [ 61, Calculated sets of parameters are listed in table 3. Some mixing coefficients of basis wavefunctions for interacting rovibronic levels are given in table 1. The molecular constants for the BO: state are comparable with the values deduced from the abc,?rption spectra [ 11, but there are essential distinctions between the calculated and previously known const nts for the Al, state [ 51. The value of the adjustable parar. ::ter tl“p is 1_220.2. It is interesting to compare it to the value qtheorfor an idealized case for which J, car- be associated with the quantized value J,(J,+ 1) [ 161. In this case and for the interacting states BO: and Al, we have ?liheor=fi. 4‘h”“‘=[(J*+SZ)(Ja-~+l)]“2 We note that deperturbed vibrational terms for v=O levels of the BO: and Al, states are approximately equal, So the difference between perturbed and deperturbed terms is almost the J-independent value AT,= P2 (B) / [&( BO: ) -I?,-,( Al,) 1. Therefore in this case the experimentally observed rovibronic levels of the BO: and Al, states can be expressed as a Dunham expansion with deperturbed rotational constants and the shift of the vibronic terms will equal AT, [6].
4. The Land6 factors Taking into account the Hamiltonian presented as follows:
considered
above, the g factors for the BO: and Al:
states can be
1) >
g<,,,m)ti=T 2CoC, Gp (W;>I,/%=&C:G,IJ(J+
(4)
where Co, C, are the mixing coefficients and G_ and G, are the corresponding electronic matrix elements If the interaction is not so strong and the explicit form of the mixing coefficients is used, we obtain ~~,,,,,=~G-v(~JI
>
l/R’ly;)(~~lG)/~,,
[ 141.
(5)
where A,, is the difference between deperturbed rovibronic terms of interacting levels. Taking the value G_ = 2~ and the mixing coefficients obtained from the term values, the g factors for the rovibronic levels of BO,f and A 1: mixed states have been calculated (see eqs. (4) and ( 5) ). These values and experimental g factors are presented in table 1.
Table 3 The deperturbed molecular constants (cm-‘) of BO: and Al, states of 13’Te2a)
T, W W& WY. B, a.
BO: state
Al, state
22203.5( 1.6) 163.5( 1.2) 0.563(0.045) -0.042(0.009) 32.58(0.04)x 1O-3 1.35(0.05)X 1o-4
22209.2(1.9) 155.9( 1.3) 2.57(0.24) 0.053 (0.010) 32.16(0.03)xlO-’ 2.17(0.07)xW4
a) The values in parentheses are twice the standard deviation.
292
CHEMICAL PHYSICSLETTERS
Volume 166, number 3
23February1990
So only states of the same parity and nuclear statistics would be mixed by the magnetic field. For the Al; state the g factor is g,= -G,/.J(.J+ 1). The experimental value of the g factor for v=2, J=96 of the A I ; state is - 2 x 10m4,therefore G.=2. Consequently, this g factor can be expressed as -2/J(J+ 1). This equation is equal to the theoretical one for the LandC factors for the F2 component of a 3C; state [ 131.
5. Intensity distributions in the BOG-Xl, transition For interacting BO: and A 1: states the matrix element of the electric dipole operator for the BO: -X 1, transition is
~~*I~l~~g~=~~OI~~OU+-x,,I+~,ICIAI”-XI~Il 9
(6)
where
~n*)=CoIBO:)+C,
IAl:),
(7a)
d,=d,,+_,,,=Re,o:_,,,(R~~~:;J”)(v,Ivl;.,>cr(J,~,~=-1).
(7b)
d,, =&WI.- -ReA,._x,,(R~~JJ”)(v;Iv[;“)cy(JI,~,A8=O).
(7c)
Here, Re( R ;JJ”) denotes the dependence of the electronic dipole transition moment on the Rsp and IYare direction cosine matrix elements [ 191. Finally, relative rotational line intensities within a given band are
centroid [ 181
Ip/l~=(vp/v~)3[(J’+2)/(5’-l)][1+~J2J’lo]*/[1-~J2olJ1]*,
@a)
I,/Io=(vp/yo)3[(J’+2)/(25’+1)][1+X~~]*/[1-XJ2ISo]2,
(8b)
I,/I~=(v,/v~)3[(I’-1)/(25’+1)][1-~~~]~/[1-~J2/so]~,
(8~)
where x= (G/Co)(Re~~,x,,
lRe,,:-,,,)((v;Ivl;~>/(v,IV[;-
>) s
(9)
The perturbation model has been used for interpretation of the relative intensities of LIF spectra in the BO:-Xl, transition from v=O, J= 179; V= 1, J=243; v=3, J=251; ~5, J= 103; ~5, J= 137 of 130Te2which have been measured [ 6,121. The experimental and calculated (for nonperturbed and perturbed approximations) relative line intensities for one of the progressions (v=5, J= 103) are given in table 2. As can be seen, the perturbation model improved the agreement with the experimental data. It is clear (see eq. (9 ) ) that the intensity distribution depends on the degree of mixing of the interacting states (C, /Co) and on the relative probabilities of the vibronic transitions. Obviously, perturbations in the intensity distribution are more pronounced in a “weak” transition, when it is mixed with a “strong” transition. It is interesting to note that for Q-branch lines the intensity distribution is determined by the value [ l(Cl/Co) (d,,/d, )dm]*, which is equal to 1 for experimentally observed transitions (J’ > 100) [6,12]. Thus the Q-branch line intensities have been used to obtain the deperturbed dependence of the transition moment on the R-centroid for the BO:-Xl, system: Re,,o:_x,,(R$J”) =0.907- 1.36(RsJ” -5.156). On the contrary, the R- and P-branch line intensities in such mixed transitions permit us to calculate the value and sign of the ratio d,,/d,. For a BO: -Xl, transition the ratio of the parallel and perpendicular transition moments has been found to equal 202 5.
293
Volume 166, number 3
CHEMICAL PHYSICS LETTERS
23 February 1990
6. Conclusion We note that the perturbation model allowed us to fit energetic, magnetic and radiation characteristics of the BOZ and A I u states in a unified way. But taking into account the small number of the experimental points, this model should not be assumed to be absolutely correct. The Land6 factors and rotational distribution of the intensity are very sensitive to small perturbations of the molecular states. So the perturbation model can be improved by systematic and accurate measurements of these “‘Te2). In particular, these results may parameters (in dependency on v and J) for different isotopes ( ‘Te2, throw some light upon the nature and molecular constants of the poorly examined excited 1, state that lies near in energy to the states considered [ 61.
Acknowledgement The authors wish to thank 1-P. Klinzare and Dr. M.Ya. Tamanis for assistance with the experiments reported here and for providing unpublished results of the Land6 factor measurements.
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