Molecular Spectra and Molecular Structure - Lec 19S

Lecture # 19 Supplement Contents A. A. A Model for the Perturbations and Fine Structure of the Π States of CO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 B. Factorization of Perturbation Parameters . . . . . . . . . . . . . . . . . 2 C. The Electronic Perturbation Parameters . . . . . . . . . . . . . . . . . 3 A Model for the Perturbations and Fine Structure of the Π States of CO This paper reports the results of an analysis of the numerous perturbations of the CO a3 Π and A1 Π states, which belong to the (σ1s)2 (σ ∗ 1s)2 (σ2s)2 (σ ∗ 2s)2 (π2p)4 (σ2p) (π ∗ 2p) electronic con­ figuration (abbreviated σπ ∗ ), by the a� 3 Σ+ , e3 Σ− , d3 Δi , I1 Σ− and D1 Δ states, which belong to the (σ1s)2 (σ ∗ 1s)2 (σ2s)2 (σ ∗ 2s)2 (π2p)3 (σ2p)2 (π ∗ 2p) configuration (abbreviated π 3 π ∗ ). As many data as possible from the absorption, emission, and radio frequency spectra involving these states were combined in a uniform and systematic analysis. In several cases it was possible to use earlier data from the work of Gerö and Szabo[3] to augment the modern studies. The vibronic levels fitted are listed in Table I. The letters adjacent to each level indicate the sources of the data. The 47 horizontal rows contain the combinations of vibronic levels treated by degenerate perturbation theory. The choice of which levels to include in each of the groups was usually determined by selecting all of the nearest and strongest perturbers of a given a3 Π or A1 Π level. (The vibronic levels of the A and a states conveniently never occur at the same energy.) Therefore, the fitted a3 Π and A1 Π constants reported here should be regarded as fully deperturbed with respect to all of the nearest interacting levels. Extensive use was made of a nonlinear least squares fitting procedure which has been described 1 Page 2 earlier. The elements of the effective Hamiltonian matrix are given by Wicke et al.[2] The analysis of perturbations of the CO a3 Π and A1 Π states has led to two important conclusions. (i) For perturbations between vibronic levels belonging to a given pair of electronic states the perturbation matrix element is the product of a vibrational factor with a constant electronic factor. (ii) Simple, single-configuration arguments successfully predict the sign and relative magnitude of each of the electronic factors for perturbations between levels of each pair of electronic states. Thus all of the perturbations considered here can be related to two constants which are joint properties of the electronic configurations. It is now possible to calculate the interaction energy between any rovibronic level of one electronic configuration with those of the other configuration whenever the vibrational wave-functions are known. B. Factorization of Perturbation Parameters All perturbation parameters are listed in Table II. The electronic part of each perturbation param­ eter was obtained by dividing the spin-orbit parameter, A or α, by the vibrational overlap �v|v � �, �v|r−2 |v � � ≡ �v|B|v � � = Bvv� . For extremely weak perturbations, the beta parameters, denoted with an asterisk, were calculated by multiplying an average value of the assumed constant electronic factor by the proper vibrational factor. Also included in Table II are the r–centroids, �v|r|v � �/ �v|v � � which indicate the internu­ or by dividing the rotation-electronic parameter, β, by h 8π 2 cµ clear distance of maximum vibrational overlap (stationary phase point). For perturbations between any pair of electronic states, the r–centroid is nearly constant. For a given perturbing state the r–centroids are approximately 0.3 Å greater for perturbations of a3 Π than of A1 Π. This indicates that the overlap is greater at a larger internuclear distance for perturbations of the a3 Π state than for the A1 Π state. This result can be rationalized by examining the potential energy curves for CO. The inner wall of the A1 Π state runs close to and parallel to the inner walls of the perturbing a� , e, d, D, and I states, whereas the curves of the perturbing states cross the a3 Π state on the outer wall. For the pairs of states for which multiple determinations of the electronic part of the perturbation parameters were possible, the independence of this constant electronic factor with respect to v, v � is demonstrated in Table II. Thus, it is possible to partially evaluate second order effects by summations over all known vibrational levels of a particular electronic symmetry. Second-order constants for the a3 Π state are calculated and discussed by Wicke et al.[2] Page 3 C. The Electronic Perturbation Parameters The relative signs and magnitudes of the electronic perturbation parameters have been derived considering only two electronic configurations: σπ ∗ π3π∗ (σ1s)2 (σ ∗ 1s)2 (σ2s)2 (σ ∗ 2s)2 (σ1s)(σ ∗ 1s)2 (σ2s)2 (σ ∗ 2s)2 (π2p)4 (σ2p)(π ∗ 2p) (π2p)3 (σ2p)2 (π ∗ 2p) a3 Π, A1 Π a Σ+ , e3 Σ− , d3 Δi , D1 Δ, I1 Σ− , 1 Σ+ . �3 The treatment which follows considers the six 2p electrons to the right of the line and neglects those to the left as core. The general procedures used to obtain wavefunctions in a Hund’s case a basis set and to calculate matrix elements are analogous to those given by Condon and Shortley,[4] Chapter 6. The Hamiltonian operators and symmetry operator, σv , used here are those given by Hougen[5] and are consistent with the phase convention of Condon and Shortley.[4] The complete wavefunctions of definite overall parity contain electronic, rotational, and vi­ brational parts. Consider first the electronic part. In order to maintain a consistent arbitrary phase throughout the calculation, a standard order for the complete set of individual spin-orbital quantum numbers must be defined. The standard order for the 2p orbitals chosen here was (1+ 1− − 1+ − 1− 0+ 0− 1∗− 1∗− − 1∗+ − 1∗− ) where the numerals denote the values of m� , ± de­ notes ms = ± 12 , and the asterisk denotes the (π ∗ 2p) orbital. All possible six-electron functions were formed for each electronic configuration. There are eight such functions for the σπ ∗ configuration and sixteen for the π 3 π ∗ configuration. Each function could immediately be characterized by |ΛΣ�. Functions characterized by |ΛSΣ� were then generated. Those with Λ = ±1 or ±2 and Σ = 1 could be identified as triplets by inspection. The corresponding |Λ10� and |Λ1 − 1� functions were � obtained by successively applying the ladder operator S− = 6i=1 si− (see Condon and Shortley, Chapter 8, §5 [4]). The functions with Λ = 0 were generated in the same way except, since there were initially two functions with Λ = 0, Σ = 1, the sum and difference functions were used. The singlet functions |Λ00� were formed by taking linear combinations of the original functions which were orthogonal to the triplet functions |Λ10�. The transformation properties of the Σ state functions and those with Ω = 0 under the symmetry operation σv (see Hougen §2.3 [5]) are denoted by + if they transform into themselves and by − if they transform into their negatives. It should be noted that the 3 Π0 functions, |−111� and |11 − 1� generated by the above procedure did not transform properly, therefore the sum and difference functions which do transform properly were used for the 3 Π0 ± states. The resulting functions were then anti-symmetrized with the operator A (see Condon and Shortley page 164 [4]) and are shown in Table III. The rotating-molecule wave functions were formed by multiplying the electronic part by the appropriate rotational part |ΩJM �, and, for Ω = � 0, taking sums and differences of Page 4 functions with equal |Ω| for a given electronic state. The parity of the rotating-molecule functions was determined with the operator σv , used here are those given by Hougen [5] and are consistent with the phase convention of Condon and Shortley. [4] The complete wavefunctions of definite overall parity contain electronic, rotational, and vibra­ tional parts. Consider first the electronic part. In order to maintain a consistent arbitrary phase throughout the calculation, a standard order for the complete set of individual spin-orbital quantum numbers must be defined. The standard order for the 2p orbitals chosen here was (1+ 1− − 1+ − 1− 0+ 0− 1∗+ 1∗− − 1∗+ − 1∗− ), (1) where the numerals denote the values of m� , ± denotes ms = ±1/2, and the asterisk denotes the (π ∗ 2p) orbital. All possible six-electron functions were formed for each electronic configuration. There are eight such functions for the σπ ∗ configuration and sixteen for the π 3 π ∗ configuration. Each function could immediately be characterized by |ΛΣ�. Functions characterized by |ΛSΣ� were then generated. Those with Λ = ±1 or ±2 and Σ = 1 could be identified as triplets by inspection. The corresponding |Λ10� and |Λ1 − 1� functions were obtained by successively applying the ladder � operator S− = 6i=1 si− [See Condon and Shortley (18, Ch. 8 Section 5) [4]]. The functions with Λ = 0 were generated in the same way except, since there were initially two functions with Λ = 0, Σ = 1, the sum and difference functions were used. The singlet functions |Λ00� were formed by taking linear combinations of the original functions which were orthogonal to the triplet functions |Λ10�. The transformation properties of the Σ state functions and those with Ω = 0 under the symmetry operation σv [see Hougen (Section 2.3) [4]] are denoted by + if they transform into themselves and by − if they transform into their negatives. It should be noted that the 3 Π0 functions, |−111� and |11 − 1� generated by the above procedure did not transform properly, therefore the sum and difference functions which do transform properly were used for the 3 Π0 ± states. The resulting functions were then antisymmetrized with the operator A [see Condon and Shortley (p. 164) [4]] and are shown in Table III. The rotating molecule wavefunctions were formed by multiplying the electronic part by the appropriate rotational part |ΩJM �, and for Ω = � 0, taking sums and differences of functions with equal |Ω| for a given electronic state. The parity of the rotating-molecule functions was determined with the operator σv . For the six-electron system the spin-orbit operator can be written HSO = 6 � i=1 ai �i · si (2) Page 5 where 1 1 � · s = �z sz + �+ s− + �− s+ 2 2 a ≡ �±1|a�± |0� = �0|a�� | ± 1� . (3) (4) The matrix elements of HSO were evaluated according to the procedure given by Condon and Shortley, Chapter 6 §6.[4] The six-electron operator corresponding to BL± S� : BL± S� = B � 6 � i=1 �� �i± 6 � j=1 � sj� � =B 6 � �i± si� + i=1 b ≡ �±1|�± |0� = �0|�� | ± 1� . 6 � � (�i± sj� + �j± si� ) (5) i>j=1 (6) The matrix elements of the 2nd sum of the BL± S� operator were evaluated by the procedure given by Condon and Shortley Chapter 6 §7. [4] �6 The six-electron operator for −BJ± L� is simply −BJ± i=1 �i� . The matrix elements of J± were taken from Hougen page 9. [5] The perturbation matrix elements written in terms of the parameters a and b are summarized in Table IV. The relationships of the perturbation parameters defined by Wicke et al. [1] to the parameters a and b are given in Table V. Also included in the last column of Table V are the experimental values for a and b determined from perturbations between various pairs of electronic states. The close agreement among the experimentally determined values of a and b is striking. Page 6 Table I: A1 Π Perturbation Parameters A1 Π (v) Perturber (v � ) 0 a� (9) 1 a� (10) 2 a� (11) 3 a� (13) 4 a� (14) 5 a� (16) 6 a� (17) 7 a� (19) 8 a� (20) 10 a� (23) 12 a� (26) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 e(1) e(3) e(4) e(5) e(7) e(8) e(10) e(11) e(12) e(14) e(15) e(17) e(18) e(19) e(21) e(22) e(24) e(25) e(27) A (cm−1 ) A/ �v|v � � (cm−1 ) 1.41* 2.890(29) -21.54(22) 3.93* -4.058(37) -20.89(19) -4.21* 4.15* 3.996(10) -20.87(5) -3.64* -3.082(18) -20.62(12) 2.058(35) -20.04(34) -1.25* r–centroid (Å) 1.1231 1.1297 1.1363 1.1295 1.1362 1.1300 1.1367 1.1310 1.1381 1.1401 1.1422 8.708(6) 2.07* 7.416(32) 5.51* -4.41* -0.469(31) 0.65* -2.36(24) -4.03* 3.48* 4.328(25) -3.79* -3.78* -3.13* 3.07* 2.148(32) -2.22* -1.24(5) 1.25* 1.2890 1.2602 1.2815 1.2947 1.2855 1.3504 1.3392 1.2650 1.2830 1.2723 1.2841 1.2747 1.2854 1.2971 1.2882 1.3017 1.2933 1.3128 1.3049 -24.73(2) -24.92(11) -17.1(11) -26.2(27) -25.28(15) -23.68(35) -23.5(9) Page 7 Table I: (continued) A1 Π (v) 0 1 2 3 4 6 8 9 11 13 16 18 Perturber (v � ) d(4) d(5) d(7) d(8) d(9) d(12) d(15) d(16) d(19) d(22) d(26) d(29) A (cm−1 ) -12.439(29) -9.769(39) 6.2* 0.532(64) -4.04* 6.338(11) -6.074(39) 5.15* 3.551(18) -2.234(65) -1.15* 1.200(41) A/ �v|v � � (cm−1 ) -33.70(8) -33.90(14) β(cm−1 ) β/ �v|B|v � � (unitless) .114(2) 0 1 2 4 6 7 8 9 10 11 13 14 15 16 I(1) I(2) I(3) I(6) I(9) I(10) I(12) I(13) I(15) I(16) I(19) I(21) I(22) I(24) -.0539(9) .056* .0231(55) .0121(10) -.031* -.036* .034* .0212(65) -.027* -.0128(36) .006* -.0068* -.0032* -.0025* 1 D(1) .0746(25) -28.3(34) -34.20(6) -33.51(22) -32.31(16) -37.0(11) a− .061(15) .156(13) .091(28) .091(26) a− Uncertainties in ( ) correspond to one standard deviation. * Fixed at calculated values. a. Vibrational wavefunctions not available. ˚ r–centroid (A) 1.2200 1.2298 1.2226 1.2994 1.2193 1.2227 1.2221 1.2308 1.2290 1.2309 1.1957 a− 1.2929 1.2966 1.3105 1.2707 1.2952 1.3083 1.2987 1.3117 1.3028 1.3196 1.3514 1.3376 1.2151 1.1898 a− Page 8 Table II: a3 Π Perturbation Parameters a3 Π(v) Perturber(v � ) 4 5 6 7 8 10 13 15 a� (0) a� (1) a� (3) a� (4) a� (5) a� (8) a� (12) a� (15) α (cm−1 ) -7.476(9) -8.016* 4.226* 5.601(16) 4.64* -4.066* 2.183* -1.959* 11 14 e(2) e(6) -3.956(34) -4.52* 9 12 15 d(2) d(6) d(15) -9.258(21) 1.856(57) 0.83* I(0) I(1) I(4) I(5) A(cm−1 ) -0.886* -2.168* -9.88(32) -9.42(9) 10 11 13 14 β (cm−1 ) .0819(4) .0874* -.0473* -.0609(6) -.0506* .0447* -.0239* .0216* .0353(12) .0405* α/ �v|v � � (cm−1 ) -17.77(2) β/ �v|β|v � � (unitless) 0.1544(8) -17.53(5) 0.1512(15) -17.55(15) 0.1587(54) 1.5759 1.5895 .0889(32) -24.84(6) -.019* -22.8(7) -.008* 0.222(8) —– r–centroid (Å) 1.3955 1.4058 1.3833 1.3964 1.4095 1.4026 1.4160 1.4129 1.5122 1.4785 1.4202 A/ �v|v � � (cm−1 ) -24.7(8) -23.61(23) 1.5856 1.5965 1.5924 1.6045 Page 9 Table III: Normalized, antisymmetrized wavefunctions for the σπ ∗ and π 3 π ∗ configurations State Ω wavefunctions for . . . (π2p)4 (σ2p)(π ∗ 2p) 3 +2 A |1+ 1− − 1+ − 1− 0+ 1∗+ � Π2 −2 A |1+ 1− − 1+ − 1− 0− − 1∗− � 3 Π1 +1 −1 + |1+ 1− − 1+ − 1− 0+ 1∗− �] A √12 [|1+ 1− − 1+ − 1− 0− 1∗+ � A √12 [|1+ 1− − 1+ − 1− 0− − 1∗+ � + |1+ 1− − 1+ − 1− 0+ − 1∗− �] 3 Π0 0+ 0− A √12 [|1+ 1− − 1+ − 1− 0− 1∗− � A √12 [|1+ 1− − 1+ − 1− 0− 1∗− � 1 Π +1 −1 3 Δ3 +3 −3 − |1+ 1− − 1+ − 1− 0+ 1∗− �] A √12 [|1+ 1− − 1+ − 1− 0− 1∗+ � A √12 [|1+ 1− − 1+ − 1− 0− − 1∗+ � − |1+ 1− − 1+ − 1− 0+ − 1∗− �] . . . (π2p)3 (σ2p)2 (π ∗ 2p) wavefunctions for A |1+ 1− − 1+ 0+ 0− 1∗+ � A |1− − 1+ − 1− 0+ 0− 1∗− � 3 Δ2 +2 −2 + |1+ 1− − 1+ 0+ 0− 1∗− �] A √12 [|1+ 1− − 1− 0+ 0− 1∗+ � A √12 [|1− − 1+ − 1− 0+ 0− − 1∗+ � + |1+ − 1+ − 1− 0+ 0− − 1∗− �] 3 Δ1 +1 −1 A |1+ 1− − 1− 0+ 0− 1∗− � A |1+ − 1+ − 1− 0+ 0− − 1∗+ � 1 Δ +2 −2 − |1+ 1− − 1+ 0+ 0− 1∗− �] A √12 [|1+ 1− − 1− 0+ 0− 1∗+ � A √12 [|1− − 1+ − 1− 0+ 0− − 1∗+ � − |1+ − 1+ − 1− 0+ 0− − 1∗− �] Σ+ +1 0− A √12 [|1+ 1− − 1+ 0+ 0− − 1∗+ � A 12 [|1+ 1− − 1− 0+ 0− − 1∗+ � + |1− − 1+ − 1− 0+ 0− 1∗+ � A √12 [|1+ 1− − 1− 0+ 0− − 1∗− � + |1+ − 1+ − 1− 0+ 0− 1∗+ �] + |1+ 1− − 1+ 0+ 0− − 1∗− � + |1+ − 1+ − 1− 0+ 0− 1∗− �] + |1− − 1+ − 1− 0+ 0− 1∗− �] A √12 [|1+ 1− − 1+ 0+ 0− − 1∗+ � A 12 [|1+ 1− − 1− 0+ 0− − 1∗+ � − |1− − 1+ − 1− 0+ 0− 1∗+ � A √12 [|1+ 1− − 1− 0+ 0− − 1∗− � − |1+ − 1+ − 1− 0+ 0− 1∗+ �] + |1+ 1− − 1+ 0+ 0− − 1∗− � − |1+ − 1+ − 1− 0+ 0− 1∗− �] − |1− − 1+ − 1− 0+ 0− 1∗− �] 3 −1 3 Σ− +1 0+ −1 − |1+ 1− − 1+ − 1− 0+ − 1∗+ �] + |1+ 1− − 1+ − 1− 0+ − 1∗+ �] 1 Σ+ 0+ A 12 [|1+ 1− − 1− 0+ 0− − 1∗+ � + |1− − 1+ − 1− 0+ 0− 1∗+ � − |1+ 1− − 1+ 0+ 0− 1∗− � − |1+ − 1+ − 1− 0+ 0− 1∗ �] 1 Σ− 0− A 12 [|1+ 1− − 1− 0+ 0− − 1∗+ � − |1− − 1+ − 1− 0+ 0− 1∗+ � − |1+ 1− − 1+ 0+ 0− − 1∗− � + |1+ − 1+ − 1− 0+ 0− 1∗− �] Page 10 Table IV: Electronic Perturbation Matrix Elements. ���6 �� 3 + � �3 � Σ1 ±, v � = 1 a �v|v � � − Bvv� b � Π ±, v a � · s + B(L S + L S ) 1 i i i + − − + i =1 � �� �� �3 � 4 1 � � 6 ai �i · si + B(L+ S− + L− S+ ) � 3 Σ− Π ±, v ±, v = −√4 a �v|v � � + B√ 1 vv � b ���i6=1 �3 �� 3 1 � 1 � � � � B(L+ S�− + L−√S+ ) Δ1 ±, v = 4 2a �v|v � − 2Bvv� b �3 Π1 ±, v ��6 i=1 ai �i · s�i 1+ − 1 � � 2a �v |v � � ai �i · si � Σ −, v�� = − 4 √ �3 Π0 −, v ��i=1 6 1 1 � � � v� = 4 2a �v |v � � �1 Π2 ±, v��6 i=1 ai �i · s�i 3 Δ±, 1 � � � � + 1 , , v �= 4 a �v|v � �1 Π±, v ��i6=1 ai �i · si � 3 Σ− 1 � � � a �v|v � � �1 Π±, v ��i6=1 ai �i · si � 3 Σ1 ±, v� � = −14√ Π±, v � i=1 ai �i · si � Δ1 ±, v = − 4 2a �v|v � � 1 �1 Π−, v |−B(J+ L− + J− L+ | 1 Σ− −, v � � = −Bvv� bx 2 1 �1 Π±, v |−B(J+ L− + J− L+ | 1 Δ±, v � � = Bvv� b(x − 2) 2 x = J(J + 1) Perturbations 3 Π, 3 Σ+ 3 Π, 3 Σ− 3 3 a = −4 α2 / �v|v � � a = 99.3 b = 0.222 Π, 1 Σ b = β2 / Bvv� � � a = −4 A− 01 �v|v � √ a = 2 2 A21 / �v|v � � � � a = −4 A+ 10 �v|v � � � a = −4 A− 10 �v|v � √ a = −2 2 A12 / �v|v � � � − Bvv� b = 2 β10 Π, 1 Δ b = −β12 / Bvv� Π, 3 Δ Π, 1 Σ− 3 Π, 1 Δ 1 Π, 3 Σ+ 1 Π, 3 Σ− 1 Π, 3 Δ 1 1 a Table V: Electronic Perturbation Paramaters a Correspondences Experimental Value √ +� � a = 100.3 a = −4 2 α0 �v|v � √ � b = 0.217 b = 2 B0+ Bvv� √ � a = −4 2 α0− �v|v � � a = 99.3 √ � b = 2 β0− Bvv� b = 0.224 a = 94.8 no perturbation analyzed a = 83.4 a = 99.0 a = 95.8 b = 0.228 vibrational wavefunctions not available for 1 Δ For definitons of the parameters α, β, etc. see Freed,[6] Wicke et al.[2] and Field [1].