SCF-Xα-SW and X-ray emission study of the electronic structure of some phosphorus compounds

JOURNAL OF ELECTRON SPECTROSCOPY and Related Phenomena

ELSEVIER

Journal of Electron Spectroscopyand Related Phenomena 77 (1996) 291-305

SCF-X -SW and X-ray emission study of the electronic structure of some phosphorus compounds Leonid N. Alexeiko*, Oleg L. Shcheka Far Eastern Technological Center, 41 Gogolya Street, Vladivostok 690600, Russia

First received 20 December 1994; accepted in final form 20 September 1995

Abstract

High-resolution ultra-soft X-ray emission spectra of some phosphorus compounds were measured. Calculations by the SCF-X~-SW method were used for analysis of experimental data. A satisfactory agreement of theoretical and experimental results was ensured only for calculations in spd-basis. This conclusion is true for compounds of fourcoordinated phosphorus (PO43-, OP(CH3)3, SP(CH3)3, OP(OCH3)3). For PH3, P(CH3) 3 and P(OCH3) 3 the extension of the basis does not lead to sufficient improvement in the simulated spectra. The quality of the calculations was estimated by comparing the distribution of P 3s, P 3d populations on the valent MO of molecular ions (hole in P 2p level) and to intensities of PL2,3 spectral bands. Satisfactory agreement of experimental and theoretical data obtained allowed us to estimate a degree of 3d orbital participance in construction of chemical bonds for neutral molecules containing phosphorus atoms with various coordination numbers.

Keywords." Electronic structure; SCF-X~-SW; X-ray emission spectrum

1. Introduction

The large number of papers directed to the description of the electronic structure of phosphorus compounds [1-3] is due to the difficulty of experimental data analysis, especially for X-ray. emission spectra. The question about phosphorus 3d orbital role in electronic density distribution and chemical bond construction is more complicated. Under the transition from three- to fourcoordinated phosphorus compounds, the significance of P 3d atomic orbitals (AO) changes in principle [4]. In this paper we study the electronic structure of * Corresponding author.

molecules PH3, P(CH3)3, OP(CH3)3, SP(CH3)3, 3 P(OCH3)3, OP(OCH3) 3 and anion PO 4- by the method of ultra-soft X-ray emission spectroscopy. For experimental data simulation we use the SCF-X~-scattered waves (SW) calculations in sp- and spd-bases. The aim of this paper is to estimate the role of P 3d AOs in valent occupied orbital construction for three- and four-coordinated phosphorus compounds. We simulated PL2,3 spectra calculating the electronic density distribution in molecular ions (a "hole" in P 2p level). With satisfactory results for such a simulation we had the possibility to determine the role of P 3d orbitals in the P - X (X = C, O, S, H) chemical bonding for neutral molecules.

0368-2048/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 0368-2048(95)02550-2

292

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Table 1 SCF-Xo-SW calculation of PH 3 electronic structure (energies (ei), ionization potentials, P 3s, 3p, 3d, H Is, 2p populations of MOs and effective atomic charges (q)) and PLL3 spectrum (energies (E) and intensities (J) of bands) MO

2al

le lal P2p P2s

Pls

qp

qH

Basis

I II III I II III I II III I II III I II III I II III I II III I II III

-El, eV

6.38 5.94 5.43 9.23 9.31 9.07 16.21 15.67 15.54 123.67 123.46 122.45 171.44 171.21 170.20 2075.11 2075.14 2074.16 0.261 0.330 0.372 -0.087 --0.110 -0.124

IP, eV

10.38 9.70 9.22 13.40 13.56 13.52 20.70 20.10 20.21 138.66 138.50 138.87

P

H

s

p

d

s

p

14.93 14.28 14.08 0 0 0 60.37 60.79 58.47

66.52 66.89 64.80 45.61 37.07 37.24 3.86 3.75 4.71

0 0.01 0.01 0 6.84 7.46 0 0.02 0.02

18.55 18.82 16.99 54.39 56.09 51.29 35.77 35.44 31.00

0 0 4.13 0 0 4.02 0 0 5.80

2. Experimental High-resolution ultra-soft X-ray emission spectra for all c o m p o u n d s were o b t a i n e d on the s p e c t r o m e t e r " S t e a r a t " at the I n s t i t u t e o f I n o r ganic C h e m i s t r y ( N o v o s i b i r s k , Russia) [5]. This s p e c t r o m e t e r was e q u i p p e d with a c o p p e r a n o d e a n d a t u n g s t e n cathode. T h e w o r k i n g regime o f X - r a y t u b e was U = 6 kV, I = 0.8 A. O w i n g to the absence o f c r y s t a l - a n a l y s e r s h a v i n g a g o o d reflecting c a p a c i t y a n d a high r e s o l u t i o n in the energy region 100-140 eV, r e c o r d i n g PL2,3 X - r a y emission spectra is a very difficult task. W e used a p s e u d o c r y s t a l (a lead(IV) c o m p o u n d with o r g a n i c li.gands (2d ~ 131 A)) as the dispergating element. T h e usual m e t h o d o f this crystal p r e p a r a t i o n is c o n c l u d e d b y successive d e p o s i t i o n o f s o m e s o a p film layers on the m i c a plate. A high intensity o f reflected r a d i a t i o n is achieved b y use o f m u l t i l a y e r p s e u d o c r y s t a l s ( 1 5 - 2 0 films), b u t owing

E/eV

J × 10-3

128.28 -128.65 125.26 -124.35 117.96 -117.66

0.938 -0.939 0 -0.370 4.617 -4.219

to deorientation o f films from each other, the energy resolution o f recorded spectra deteriorates with time. The first time we used the pseudocrystal it consisted o f four films. In these conditions the high-resolution spectra are recorded in a short time only, since the resolution a n d intensity obtainable decrease rapidly with use (in time). F o r subsequent increasing spectrum intensity, at lower resolution, we used a copper a n o d e covered by thin graphite layer. D e t e c t i o n o f X - r a y p h o t o n s was by m e t h a n e p r o p o r t i o n a l c o u n t e r ( p ~ 200 Torr). T h e p h o s p h o r u s c o m p o u n d s were o n the s e c o n d a r y a n o d e (a c o p p e r plate). This a n o d e was c o o l e d by liquid nitrogen. A m o r e detailed d e s c r i p t i o n o f the e x p e r i m e n t is given in Ref. [5].

3. Theory T h e theoretical calculations o f the electronic

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structure of phosphorus compounds and the simulation of X-ray emission spectra were carried out by the SCF-X~-SW method on sp- and spd-bases. Ionization potentials (IP) of valent molecular orbitals (MO) and core P 2p-level were calculated approaching the intermediate state. We can comment on the high accuracy of the ionization energy estimation: for example for molecule PH 3 IP of P 2p-level in basis III is 137.869 eV (Table 1). This IP, calculated as the difference of full energies of molecule and molecular ion (P 2p-vacancy) ground states, is 136.885 eV. Therefore the difference of P 2p-level IPs calculated by the two approaches is less than 0.7%. The transition energies for X-ray emission PL2,3 spectra were determined as differences of valent MOs and P 2p-level IPs. The probabilities of X-ray transitions were calculated as: I r (E) ~ ~ ~ I(U]'IrjlU2p)I 2 Jg i$ where Uir is the valent MO transformation on the ith line of nonreducible representation F, r i is the component of radius-vector (x,y,z), UEv is the core 2p-function, g is the dimension of nonreducible representation F. Wave functions U2p and Uir were chosen by the calculations of M + ionization states with a hole in the 2p-level. Such states correspond to initial states of emission transitions that give us the possibility to use valent and core wave functions relaxed under the core vacancy creation. The analysis of charge distribution in molecules has been done on the basis of MO population calculations. Similar calculations are not a simple task for the X~-SW method because wave functions in this method are not linear combinations of atomic orbitals (LCAO) and have radial parts depending on the energy. Under the population calculations, we used the method of molecule intersphere and external region charge relation to atoms [6]. MO populations obtained by this method are close to Mulliken's MO populations. Atomic effective charges were calculated as the sum of AO populations for every atom. The molecule PH3 has been calculated by different methods (and SCF-X~-SW too [71]). In Ref. [7] this molecule had been calculated in different

293

2~ 4

•

~20

140

IP,eV

'

2.0

2.~,~ ,t3o

)

4

~eV

'

,IO

Fig. 1. Experimental PL2, 3 (a), PK;~ (d) and theoretical PL2, 3 spectra of molecule PH3 calculated in spd-(b) and sp-(c) bases.

approaches. Both the basis of partial-wave decomposition of wave function and parameters of overlapping atomic spheres were varied. In the present work, under fixed relations of atomic sphere radii and degree of their overlap, optimized in [7], the main attention was given to the study of the PH 3 electronic structure and PL2, 3 X-ray emission spectrum dependence on the completeness of basis (in particular, on inclusion of P 3d-orbitals in basis). All calculations were done under fixed geometry of molecules (for PH3: Rp_H = 1.415 A, LHPH = 93.45 ° [7]). The overlap degree of atomic spheres for PH3 is as in paper [7] for the sphere parameter optimization case under the inclusion of d-functions on phosphorus atoms. Exchange potential parameters were found for atomic spheres from Schwarz's tables [8]: O~p ~ 0.7262, a H = 0.77654, c~c = 0.75928, cz0 = 0.74447, c~s -----0.72475. For molecule PH3, the calculations were repeated in three basis sets: (I) lp = 0, 1; l~i = 0; in external region, lext = 0, 1, 2; (II) le = 0, 1, 2; l H = 0; lext = 0, 1, 2, 3; (III) Ip = 0, 1, 2; l H -----0, 1,/ext ----0, 1, 2, 3. For other compounds the calculations were repeated on two bases: (I) lp = /c = /o = /s = 0, 1; / H = 0 , /ext = 0 , 1, 2, 3; (II)

294 /p:0,

L.N. Alexeiko, O.L. Shcheka/Journal of Electron Spectroscopy and Related Phenomena 77 (1996) 291-305 1,2; IC : l o

:ls

:0 ,

1; IH : 0 ; /ext : 0 , 1,

2, 3. The condition of external sphere touching of all atomic spheres was always fulfilled in our calculations. Such an approach allows one to compare our data with data obtained in analogous approaches for related molecules.

~ b

O_ P-~V

4. Results and discussion

4.1. Molecule PH3 PH 3 experimental PL2,3, PK;~ spectra and simulated PL2,3 spectra by SCF-X~-SW calculations in sp- and spd-bases spectra are presented in Fig. 1. Theoretical spectra are constructed as superimposed Lorentz curves. Their intensities correspond to transition intensities (Table 1). The energy width of the curve is 2 eV. Valent MO energies and IPs calculated in various bases are given in Table 1. The basis extension influences IPs in different manners. The inclusion of phosphorus d-functions in the basis leads to a decrease of MO 2al IP. The first IP decreases after the inclusion of hydrogen p-functions in the basis too. Table 1 displays how the external sphere affects the calculation results. For basis I the first IP is 10.26 eV. In paper [7] similar calculations gave the value 10.61 eV. This difference is explained by external sphere radii. We used bext = 3.655 a.u. in contrast to paper [7] where bext --- 3.336 a.u. The external sphere increase leads to the charge decrease in the external region of the molecule and can lead to decreasing external MO IPs. The first IP sensitiveness to the basis on hydrogen atoms indicates that the good agreement of calculated and experimental IPs in papers [7], where the hydrogen p-functions in basis were not included, is likely to be random. Second and third IPs have a weak dependence on the basis. For them a good agreement of theory and experiment was achieved. The inclusion of phosphorus d-functions in basis leads to the noticeable change of AO populations for MO le only. The contribution of P 3d AO in MO le is 6% greater and this increases after basis extension on hydrogen atoms. According to the model hypothesis [4] the small presence of P 3d population in the general distribution of the

C

%0

|

t20

Fig. 2. ExperimentalPK/3(a), PL2,3 (b) and theoreticalPL2,3 spectra of molecule P(CH3)3 calculated in spd-(c) and sp-(d) bases. electronic density in molecule PH3 is explained by a "direct" energy effect. The small increase of that population for basis III is likely to take place as a result of the "reverse" ( p ~ - d~)-interaction [4]. The extension of the basis on hydrogen atoms leads, in the main, to the redistribution of density between s- and p-AOs of hydrogen. P AO populations change weakly (<2%). A strong interaction of AOs for all valent MOs is a characteristic peculiarity of the PH3 molecule electronic density distribution. Therefore the chemical bond in PH 3 is not strong by ionic. Since, after basis extension, the atomic effective charges increase (Table 1) it is necessary to use extended bases for description of reactionary ability of even such a simple molecule like PHH. Table 1 contains the energies and relative intensities of transitions in the X-ray emission PL2,3 spectrum. The basis extension does not lead to noticeable change of these parameters for transitions 2al ~ P 2p and lal ~ P 2p. However the transition le ~ P 2p can be described only with

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295

Table 2 Energies (el),IPs (eV) and P 3s, 3p, 3d populations of molecule P(CH3)3 MOs MO

4al 4e la2 3e 2e 3al 2cq le lal P2p P2s Pls

Basis

I II I II I II I II I II I II I II I II I II I II I II I II

P s

p

d

2.24 2.11 0 0 0 0 0 0 0 0 0,15 0.09 49.95 50.20 0 0 20.26 20.02

58.34 57.44 42.43 35.90 0 0 2.56 2.63 1.80 1.48 4.47 4.19 0.02 0.02 3.63 3.69 0 1.99

0 1.43 0 4.75 0 0 0 0.12 0 1.16 0 0.74 0 0.01 0 1.13 0 0.05

the use ofspd-basis. This peak is weak in the experimental spectrum (Fig. 1). We can specify the position of the corresponding band only under the help of the experimental PKa spectrum that gave us the possibility to determine exactly the ionization energy of M O l e . Comparing the spectral regions of the transition band M O l e - A O P 2p and the full spectrum and other electronic structure parameters connected with P 3d-electrons (Table 1), we conclude that the role of P 3d AO in PH3 electronic structure description is small in quantitative contribution. The phosphorus 3d AO has a specific small contribution because, for example, the L2,3 spectrum peak, corresponding to the transition M O le A O P 2p, is caused entirely by the 3d-component of the M O l e (Fig. 1, Table 1).

4.2. Molecules P( CH3)3, OP( CH3)3, SP( CH3)3 The structure parameters of molecule P(CH3)3

-ei/eV

IP/eV

3.28 3,14 5.80 5,92 8.20 8.00 8.76 8.57 9.74 9.61 9.74 9.65 11.78 11.54 16.11 16.02 17.84 17.61 121.19 121.23 168.99 169.02 2072.30 2072.61

4.62 6.56 8.36 8.49 11.07 10.77 11.53 11.30 12.48 12.34 12.43 12.25 14.48 14.14 18.97 18.79 20.55 20.26 136.19 136.12

were taken from papers [9-11]. We assume a molecule symmetry o f C3v. The length of bonds were: R e - c = 1.844 A, R c - n - - 1 . 0 7 9 A; the angles were: / C P C = 9 8 . 8 °, / H C H = 111 °. These are average values of experimental data [9-11]. The experimental PK~, PL2,3 and theoretical PL2, 3 spectra are shown in Fig. 2. Comparing these spectra, we can see that the calculation increases the energy distance between deep MOs l a l and 2 a 1 (Table 2, Fig. 2). The energy resolution of the experimental PL2, 3 spectrum does not allow us to observe the transitions from these orbitals separately. The considerable intensity of the PL2,3 short wave peak indicates noticeable participance of transitions from MOs 4al and 4e in this spectrum. The PK~ spectrum supports the calculation data about the predominating P 3p-population of these MOs. The transitions 4al ~ P Is, 4e ~ P ls result in the peaks A and B respectively (Fig. 2). The long-wave feature C is likely to result from transitions from MOs

296

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Table 3 Energies (el), IPs (eV) and P 3s, 3p, 3d populations of molecule OP(CH3) 3 MOs MO

5e 4e 10~2 5al 3e 2e 4al 3al le 2al 1cq

P2p P2s Pls

Basis

I II I II I II I II I II I II I I1 I I1 I I1 I II I II I II I II I II

P s

p

d

0 0 0 0 0 0 0.21 0.07 0 0 0 0 2.47 3.87 30.92 31.64 0 0 10.09 9.61 17.94 13.98

11.96 9.03 18.60 18.30 0 0 7.72 0.99 8.76 8.11 2.37 0.57 22.67 23.26 0.02 0.04 2.65 2.39 3.59 2.78 11.59 10.75

0 12.47 0 0.49 0 0 0 2.34 0 0.47 0 0.41 0 2.60 0 0.13 0 0.48 0 0.44 0 5.23

3e, 2e, 3a 1. P 3p-populations of these MOs are small. Comparing the data of Table 2 and the experimental spectra in Fig. 2, we conclude that the electronic density distribution in molecule P(CH3)3 is described sufficiently well under the calculations using an sp-basis. The structure parameters of molecule OP(CH3)3 were taken from papers [12-13]. C3v symmetry is assumed. Bond lengths were: Rp_o = 1.476 A, Rp_c = 1.809 ,~; angles: LOPC = 114.4 °, /HCH = 111.0 °. The energies and IPs of valent MOs calculated in sp- and spd-bases are shown in Table 3. In contrast to molecule P(CH3) 3, for the molecule OP(CH3) 3 the basis extension decreases the phosphorus 2p level IP (~ 1 eV).

-ci/eV

IP/eV

6.94 7.25 9.90 9.21 10.82 10.28 11.41 11.25 11.59 11.04 11.99 11.49 12.38 11.77 15.46 14.57 18.64 18.11 19.84 19.20 26.99 27.01 127.41 126.05 175.22 173.81 2078.46 2077.67

9.71 10.26 12.65 12.18 13.78 13.22 14.14 14.08 14.38 13.88 14.85 14.40 15.27 15.10 18.40 17.96 21.62 21.08 22.70 22.12 30.81 31.67 141.24 140.25

Table 3 contains P 3s, 3p and 3d populations of valent MOs. The basis extension leads to noticeable change of the populations. The inclusion of P 3d-functions in the basis decreases the positive charge of the phosphorus atom and the negative charge of the oxygen atom (~ 0.35 e). The effective charges of carbon and hydrogen atoms are small and change only weakly under the basis extension. The analysis of charge distribution indicates that CH3-groups in molecule OP(CH3) 3 have small negative charges. The basis extension leads to an essential change of the simulated PL2,3 spectrum (Fig. 3). Under the use of basis I the low-energy transitions lal ~ P 2p, 2al --* P 2p, 3a 1 --* P 2p is the main contribution to the PL2,3 spectrum. With phosphorus 3d-functions included in the basis, a redistribution

297

L.N. Alexeiko, O.L. Shcheka/Journal of Electron Spectroscopy and Related Phenomena 77 (1996) 291-305 A

i

,

_q¢o

jill?_"

2A

£,5o

E:, e_V

C

of the crystal-analyser RbAP ( 2 d - 26 ,%). All OK~ spectra obtained with help of this crystal have short-wave satellites (peak S in Fig. 3). The appearance of these features is connected with the reflection peculiarities of the crystal. The OK~ spectrum short-wave peak A results from the X-ray transition MO 5e ~ AO O Is. This orbital has a large O 2p population. The high intensity of peak A supports this. The feature D of the PK~ spectrum indicates a participance of P 3p AO in the construction of MO 5e. The transition 4e ~ O ls forms the peak B of the OK~ spectrum. The PK~ spectrum peak E results from transitions from the MOs 5e, 5oq, 3e, 2e, 4al to the P ls AO. The transition 4a 1 ~ O ls explains the appearance of the OK~ spectrum long-wave feature C. The peaks F and G in the PK~ spectrum results from the transitions le, 2ch ~ P Is accordingly. The interpretation of the PL:, 3 spectrum is more difficult. The short wave peak is likely to be a result of transitions from MOs 5e, 4e, 3e, 2e, 4al to the P 2p AO. X-ray transitions 3al, le, 2a l, lax--* P 2p form the long-wave peak of PL:, 3

1

400

t2.0

4~0

E, e v

3)

Fig. 3. Experimental OK~ (a), PK;~(b), PL2,3 (c) and theoretical PL2,3 spectra of molecule OP(CH3) 3 calculated in spd-(d) and sp-(e) bases.

of peak intensities takes place: l a 1 ~ P 2p transition intensity decreases by more than 33 % whereas 2al ---+P 2p transition intensity increases by more than 26%. The basis extension has a weak influence on 2al ~ P 2p transition intensity. The large changes in the spectrum are connected with the appearance of an intense high energy peak (5e ~ P 2p transition) under the basis extension. These changes are explained by the redistribution of phosphorus s- and d-AOs contributions in population of MOs lal, 2al, 3al and the appearance of a P 3d-component in MO 5e. Fig. 3 contains the experimental OK~, PK~, PL2,3 and theoretical PL2,3 spectra of OP(CH3)3. The OK~ spectrum was recorded with the help

i

too

420

4t~O

Fig. 4. Experimental (a) and theoretical PL2,3 spectra of molecule SP(CH3)3 calculated in spd-(b) and sp-(c) bases.

298

L.N. Alexeiko, O.L. Shcheka/Journal of Electron Spectroscopy and Related Phenomena 77 (1996) 291-305

Table 4 Energies (Ei), IPs (eV) and P 3s, 3p, 3d populations of molecule SP(CH3) 3 MOs MO

5e 4e la2 5aj 3e 2e 4al 3al le 2cq lal

P2p P2s

Pls

Basis

P

-Ei/eV

s

p

d

I II I II I II I II I II I II I II I II I II

0 0 0 0 0 0 0 0,25 0 0 0 0 0.66 0.05 26.19 31.00 0 0

3.30 1.91 35.04 30.04 0 0 27.00 20.30 2.66 3.49 3.62 2.91 3.10 6.15 4.38 1.10 4.15 4.27

0 7.44 0 2.41 0 0 0 3.36 0 0.37 0 0.93 0 0.25 0 0.10 0 0.97

4.48 5.84 7.69 7.93 9.47 9.34 7.60 8.54 9.97 9.91 10.75 10.74 10.63 10.73 12.58 12.85 17.36 17.36

I

6.98

10.05

0

16.44

II I II I II I II I II

0.78 33.89 34.97

9.98 0.01 0.26

1.75 0 0.24

spectrum. Analysing this peak shape we can conclude that the P 3s contribution to MO la I is likely to be less than calculated in spd-basis. The high intensity of the short-wave peak of the experimental PL2,3 spectrum and the results of the theoretical description of the MOs structure allow us to confirm that the electronic structure of molecule OP(CH3)3 can be explained only on the basis of calculations in spd-basis. The structure parameters of molecule SP(CH3) 3 are as in paper [13]: Rp_ s = 1.94 .A, Rp-c = 1.818 ,~, L S P C = 114.1 ° , L H C H

= 111 °.

The energies and IPs of valent MOs calculated with use of two bases are in Table 4. The inclusion in the basis of the P 3d-functions leads to a greater change of orbital energies (0.9-1.3 eV) for some MOs (5e, 5al, 2at) than was the case for molecule

17.38 19.64 19.75 124.63 124.98 172.43 172.73 2075.77 2076.58

IP/eV

8.44 8.50 10.74 10.81 12.55 12.32 11.42 11.33 12.98 12.81 13.73 13.66 13.89 13.48 16.25 15.67 20.47 20.37 20.40 20.16 22.84 22.59 138.94 138.84

OP(CH3) 3. The basis extension has a weak influence on IPs. The phosphorus positive charge decreases ( - 0 . 2 e) for spd-calculations. The change of sulphur effective charge is small (~ 0.1 e). Carbon and hydrogen charges change weakly. The inclusion of the P 3d-function in basis leads to an essential change in the simulated PL2,3 spectrum. Under the use of basis I the main contribution in the PL2,3 spectrum is given by two low-energy transitions (lal ~ P 2p and 3ai ~ P 2p). Under the inclusion of the P 3d-function in basis, the intensities of these transitions change weakly (<10%) but the intense short-wave part appears (the transitions 5e ~ P 2p and 4e--* P 2p). These changes are explained by the redistribution of phosphorus p- and d-AO contributions to MOs 5e and 4e.

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299

Table 5 Energies (ei), IPs (eV) and P 3s, 3p, 3d populations of molecule P(OCH3)3 MOs MO

6al 2°~2 7e 6e 5al 5e 1°~2 4e 4al 3e

3oq 2e 2al le 1otI P2p P2s Pls

Basis

I II I II I II I II I II I II I II I II I II I II I II I II I II I II I II I II I II I II

P s

p

d

7.97 11.42 0 0 0 0 0 0 7.37 7.60 0 0 0 0 0 0 3.41 2.29 0 0 15.31 15.97 0 0 16.22 14.32 0 0 19.14 16.87

45.16 47.30 0 0 0.26 0.22 5.86 5.35 3.48 2.53 0.22 0.01 0 0 0.15 0 9.84 6.66 18.15 12.49 0.15 0 5.57 4.54 2.54 2.65 6.94 6.60 3.30 3.02

0 4.75 0 0 0 4.46 0 0.39 0 0.08 0 1.02 0 0 0 1.87 0 1.22 0 2.50 0 0.06 0 2.36 0 0.01 0 3.48 0 0.32

The experimental a n d theoretical PL2, 3 spectra o f molecule SP(CH3)3 are s h o w n in Fig. 4. C o n c e r n i n g the t r a n s i t i o n energies, the agreement of theory a n d e x p e r i m e n t is better here t h a n for the molecules studied above. The reverse relation of two m a i n peaks intensities (B a n d D) for the theoretical a n d experimental spectra is explained by the overstating o f P 3d p o p u l a t i o n of M O l a l in the calculations. It is likely to be a typical mistake o f the m e t h o d for the ultra-soft X - r a y emission spectra simulation. T h u s we t h i n k that peak D is

-ei/eV

IP/eV

5.84 5.33 6.16 5.86 6.68 6.94 8.23 8.02 9.06 8.84 10.29 10.25 10.34 10.22 10.56 10.64 11.41 11.17 12.69 12.59 14.62 14.22 16.72 16.91 18.90 18.41 25.64 25.76 27.57 26.96 126.22 125.02 174.01 172.75 2077.42 2076.83

8.56 8.12 8.80 8.58 9.20 9.47 10.65 10.49 11.49 11.29 12.77 12.76 12.74 12.68 12.94 13.05 13.90 13.70 15.36 15.31 17.11 16.78 19.21 19.47 21.58 21.09 28.66 28.92 30.74 30.16 140.69 139.61

c o n s t r u c t e d as a result of t r a n s i t i o n loq ---* P 2p a n d the transitions le, 2 a l --* P 2p form the feature C. T h e m a i n c o n t r i b u t i o n to peaks B a n d A is given by the transitions 3t~ 1 ~ P 2p a n d 5e ~ P 2p, respectively. The t r a n s i t i o n s from M O s 4e, 5 a l , 3e, 2e, 4 a I have little intensities. They have a weak influence o n the spectrum structure. F r o m the energy distance between peaks A a n d B we conclude that the region o f valent M O s t r a n s i t i o n s f r o m 5e to 3c~1 is less t h a n the calculated value.

300

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I /

%

I

¢oo

~o

i

I

tqo

iE , a V

Fig. 5. TheoreticalPL2,3 spectra of moleculeP(OCH3) 3 calculated in spd-(a)and sp-(b) bases. Thus comparing the experimental and theoretical data for molecules P(CH3)3, OP(CH3)3, and SP(CH3) 3 we can say that it is necessary to use the calculations in extended (spd) basis for a proper description of the electronic structure of fourcoordinated phosphorus compounds. The role of P 3d orbitals increases for components with more electronegative atoms.

4.3. Molecules P(OCH3) s, OP(OCH3)3 The structure parameters of molecule P(OCH 3)3 are given in papers [14,15]. This molecule can have C3v or Cs symmetry. We propose C3v symmetry in our calculations. Rp_o = 1.63 A, R o - c = 1.42 ,~, Rc_r~ = 1.079 A; I P O C = 118.9 ° , / O P O = 100.5 °, I H C H = 111 °. Table 5 contains the energies of valent MOs and IPs calculated in two bases. The inclusion of P 3d-functions in the basis does not lead to any essential change of orbital energies and IPs (< 1 eV). But the order of some MOs (for example 5e and la2) changes under the basis extension. The inclusion of P 3d-functions in the basis causes the phosphorus charge to decrease almost twofold. At the same time the changes in the absolute values of the charges for the other atoms are less than 0.05 e and do not change the qualitative

pattern of charge distribution: both CH3-groups and oxygen atoms have negative charges, but under the basis extension the charge of CH 3group approaches zero [5]. The basis extension causes a strong change of the simulated PL2, 3 spectrum. Under the use of basis I the main contribution in the spectrum is given by three low-energy transitions ( l a I ~ P 2p, 2al ~ P 2p, 3al ~ P 2p). With the inclusion of P 3d-functions in the basis, the relative intensities of these transitions change by about 10%. The intensities of the two low-energy peaks ( l a l ~ P 2p and 2al ~ P 2p) are inverted. For basis II, the intensity of the high-energy part of the spectrum increases. In particular the 5al ~ P 2p transition intensity increases more than 50% and the transitions 6al --+ P 2p, 7e ~ P 2p has a noticeable intensity. Table 5 indicates that these changes are explained by the phosphorus s-, p- and d-AO contributions to the high occupied MOs. At the same time we note that for oxygen atoms the related contribution changes of p-AOs in valent MOs are considerably larger than the phosphorus AO population changes caused by the basis extension. The calculated data of P(OCH3)3 PL2,3 spectrum under the use of bases I and II are given in Fig. 5. The absence of any experimental spectrum does not allow us to draw a definite conclusion on the use of any basis. We can only note that the inclusion of P 3d-functions in the basis does not have a large influence on the spectrum shape. The inclusion of these functions in the basis leads only to the short-wave component intensity increase (Fig. 5). So the basis extension for molecule P(OCH3)3 has a qualitatively similar meaning to that for the molecules PH 3 and P(CH3)3. The structure parameters of molecule OP(OCH3)3 are in paper [16]. We propose C3v symmetry for the molecule. Rp=o = 1.477 ,~, Rp_o = 1.58 A, R o - c = 1.432 .A, Rc-H = 1.102 A; l O P O = 105 °, L P O C = 118.4 ° and L O C H = 110.5 °. Table 6 contains the energies and IPs of valent MOs calculated in two bases. Like molecule P(OCH3) 3 the inclusion of P 3d-functions in the basis does not lead to a noticeable change of orbital o

L.N. Alexeiko, O.L. Shcheka/Journal of Electron Spectroscopy and Related Phenomena 77 (1996) 291-305

301

Table 6 Energies (ei), IPs (eV) and P 3s, 3p, 3d populations of molecule OP(OCH3)3 M O s MO

Basis

-ei/eV

P s

2al 8e 7e 7al 6e la2 6al 5e 4e 5a I 3e 4aj 2e 3al 2al le lal P2p P2s Pls

p

I II I I! I |I I II

0 0 0 0 0 0 1.28 1.85

I

0

II I II I II I II I II I II I II I II I II I II I II I II I II I II I II I II

0 0 0 0.06 0.01 0 0 0 0 0.58 1.49 0 0 10.29 11.72 0 0 12.92 11.29 1.51 0.75 0 0 28.31 24.11

IP/eV

d 0 0 0.17 0.01 0.02 0.35 2.19 0.64

0 0 0 2.92 0 6.27 0 1.60

7.00 6.43 7.30 7.35 7.54 7.50 8.59 8.43

9.60 9.14 9.83 9.87 10.63 10.49 11.02 10.97

3.69

0

8.70

11.13

8.33 10.61 10.28 10.83 10.96 10.83 10.72 11.21 10.91 13.70 12.84 13.78 13.12 15.27 14.49 17.28 17.15 19.46 18.53 26.15 26.12 26.70 26.30 29.33 27.94 129.01 126.09 176.79 173.78 2080.45 2078.38

10.83 13.02 12.76 13.36 13.61 13.25 13.20 13.84 13.53 16.56 16.12 16.51 15.93 18.19 17.16 19.84 19.79 22.28 21.30 29.79 29.79 29.89 29.58 32.81 31.74 144.41 141.58

4.54 0 0 2.63 0.52 0.15 0.14 0.18 0.43 14.70 13.47 16.53 11.95 0.64 0 6.46 4.27 4.23 3.38 17.16 13.86 6.91 6.06 0.35 0.59

0.27 0 0 0 4.29 0 1.79 0 1.72 0 1.42 0 1.79 0 0.01 0 1.95 0 0.06 0 5.80 0 2.69 0 0.61

energies and IPs (less 1 eV), but the orbitals 7al, 6e and 6al, 5e are inverted. The inclusion of P 3d-functions in the basis leads to a phosphorus charge decrease ( ~ 0.5 e). The absolute values of other atoms change in limits of 0.05 e. The basis extension decreases the absolute values of O*, O, H charges. At the same

time the carbon charge increases. For basis I the charges of CH3-groups are negative (-0.14 e) but for basis II are close to zero (-0.04 e) [5]. The basis extension has a great influence on the PL2,3 spectrum shape. For basis I the main contribution in the spectrum is given by three low-energy transitions (lc~ 1 --* P 2p, 3al --* P 2p, 4al --+ P 2p).

302

L.N. Alexeiko, O.L. Shcheka/Journal of Electron Spectroscopy and Related Phenomena 77 (1996) 291-305

the calculations. This is usual for quantum chemical calculations. Moreover, an intensity inversion of transitions from high and more deep orbitals takes place. At least, the analysis of the data obtained allows us to confirm that the calculations in spd-basis describe the electronic structure of the molecule OP(OCH3) 3 better than calculations in sp-basis. In paper [5] we noted that P 2p AO ionization leads to a noticeable redistribution of phosphorus s-, p- and d-populations in valent MOs (sometimes a 50% increase takes a place). This is a typical

C

0,.

/

I

k../

k.,.., g

0.. I

~00

I

I

~20

440

~ j e_V

Fig. 6. Experimental (a) and theoretical PL2,3 spectra of molecule OP(OCH3)3 calculated in spd-(b) and sp-(c) bases.

Under the basis extension the intensity of transition lal ~ P 2p decreases by about 30%, and the intensities of transitions 3oq ~ P 2p, 4tx I ~ P 2p change weakly, but at the same time the highintensive short-wave transitions appear. In contrast to the P(OCH3) 3 PL2, 3 spectrum, for the OP(OCH3)3 PL2,3 spectrum, the basis extension leads to the appearance of more than just intense high-energy transitions. Two low-energy transitions (2a I ---*P 2p, le ~ P 2p) appear in the spectrum. Table 6 indicates that these changes are explained, in the main, by P 3d AOs contributions to the corresponding MOs. We want to note that the basis extension leads mainly to a phosphorus 3p AO population decrease. Phosphorus 3s AO populations change weakly (except for MO lal). The experimental and theoretical PL2,3 spectra of the molecule OP(OCH3)3 are shown in Fig. 6. The agreement of theory and experiment is poor. In particular, the calculations decrease the values of energies for transitions (valent MOs) - - P 2p AO. It is due to an over-estimation of the absolute values of valent MO ionization energies in

~,lo

~2.o

t5o

E , e_V

Fig. 7. Experimental PL2,3 spectra of molecules KH2PO 4 (a), Na3PO4 (b) and theoretical PL2,3 spectra of anion PO~- calculated in spd-(c) and sp-(d) bases.

L.N. Alexeiko, O.L. Shcheka/Journal of Electron Spectroscopy and Related Phenomena 77 (1996) 291-305

303

Table 7 Energies (el), IPs and P 3s, 3p, 3d populations (%) of anion PO43- orbitals. Basis III corresponds to A O populations for "hole" state (2p - l ) calculated in spd-basis MO

lq

3t 2

le

2t 2

2a I

I t2

1a I

P2p P2s Pls

Basis

I II III I II III I II III I II III I II III I II III I II III I II I II I II

-ei/eV

P s

p

d

0 0 0 0 0 0 0 0 0 0 0 0 28.34 28.18 28.09 0 0 0 24.58 22.61 32.15

0 0 0 3.04 0.63 0.06 0 0 0 22.75 20.41 25.22 0 0 0 8.76 7.51 10.27 0 0 0

0 0 0 0 8.30 9.15 0 5.82 6.88 0 0.80 0.74 0 0 0 0 2.54 2.83 0 0 0

response to the electron deficiency near the phosphorus atom owing to a created vacancy in the phosphorus core level. The low P 3s-populations of MOs 2al, 5al, 6al in the "hole" state indicates unsatisfactory calculations in sp-basis. Moreover owing to the inability of P 3s AOs to take part in the construction of e-type MOs, the transitions from these MOs can not appear in the PL2,3 spectrum simulated in sp-basis calculations, but the transitions from only al-type MOs do not explain the complicated structure of the experimental spectra [5]. 4.4. Ion POJ4 -

The anion PO3- is a fragment of the molecule H3PO 4. It has a double P=O and three single P-O

IP/eV

6.97 6.59

10.36 9.99

7.29 7.74

10.64 11.11

7.93 8.05

11.25 11.39

10.73 10.19

14.21 13.69

13.83 13.08

17.45 16.69

22.80 22.68

26.32 26.24

25.50 24.81

29.13 28.42

128.78 126.63 176.56 174.34 2080.20 2078.64

143.94 141.86

bonds: R p = O = 1.517 .A, R p _ O = 1.572 A [17]. In our calculations we used a tetrahedral structure with Rp_o = 1.545 ,~ for anion PO43-. Experimental angles: L O = P - O = 112 °, / O - P - O = 105 ° [17]. The structure parameters of the tetrahedral ion differ weakly from experimental parameters defined by the method of gas-phase electron diffraction. In the calculations, a positive charge (+3e) was introduced on the external sphere. The results of the PL2, 3 spectrum calculation agree well with the experimental data (Fig. 7). The energies of valent MOs and IPs are in Table 7. The inclusion of P 3d-functions in the basis changes the IPs weakly. For high occupied MOs these changes are less than 0.5 eV; for deep valent MOs - - 0.8 eV. We would like to note that the basis extension has a large influence on

L.N. Alexeiko, O.L. Shcheka/Journal o f Electron Spectroscopy and Related Phenomena 77 (1996) 2 9 1 - 3 0 5

304

phosphorus core level IPs. For example, the IP of the phosphorus 2p-level decreases by 2 eV with the basis extension. Table 7 indicates that the basis extension leads to a noticeable change in MO populations. The greatest changes take place for populations of MOs 3t2 and le. An increase of the d-AO population of 8.3 and 5.8% respectively, occurs for MOs 3t2 and le, along with a decrease of the oxygen 2p-AO contribution (~ 5%). We want to note that the increase of the phosphorus d-AO population does not lead to noticeable changes of P 3s- and P 3p-AO populations but it does change oxygen 2s- and 2p-populations. The valent MO populations for the "hole" state (P 2p -1) with the inclusion of P 3d-functions in basis are in Table 7 under the title "basis III". These populations indicate the valent electron density redistribution caused by the vacancy creation in the P 2p-level. The effect of relaxation has a weak influence on the phosphorus P 3d-population, but a stronger effect on s- and pAOs of phosphorus and oxygen. It appears that the qe change with formation of the P 2p-vacancy 6~

s d' -

-

~-- ~

40a'

q ="

8 ~' o,~l

/.~o. 4

6 ~x~ c~~'

S-ix I t4~ ~

3o, I

,~o. I

O,

g

c

IP Fig. 8. The diagramof anion PO43- levelsfor configurationsof symmetryTd (a), C3v(b) and Cs (c).

increases the phosphorus effective charge only by 0.28, that is ~ 0.7 e of the positive charge caused by 2p-hole creation is screened by charge accumulation from oxygen atoms and the intersphere region. However, in contrast to atoms of transition metals, full core vacancy screening does not take place for phosphorus. The basis extension leads to significant change in the PL2,3 spectrum. Under the use of basis I only two transitions are observed in the PL2,3 spectrum (lcq ~ P 2p and 2ch ~ P 2p). Under the inclusion of P 3d-functions in the basis this spectrum becomes more complicated. It contains a short-wave component and the relative intensities of the two low-energy transitions change weakly. The experimental PL2,3 spectra of KHzPO4, Na3PO 4 and theoretical PL2,3 spectra of pO34simulated by calculations in sp- and spd-bases appear in Fig. 7. Our KHzPO 4 PL2,3 spectrum has better energy resolution than the analogous spectrum published in paper [18]. The experimental spectra are more complicated than theoretical spectra since the latter were calculated for the ion PO 3- (Td symmetry). The molecules Na3PO4 and KHzPO 4 have lower symmetry (C3v and Cs respectively). The decrease in symmetry leads to MO splitting and some destabilization. Fig. 8 shows the levels for ion PO 3 of three configurations. It displays the MO splitting under the symmetry reduction. The level order for Td-configuration was taken from X~-SW calculations. The levels of lower-symmetry configurations for given orbitals have, as a rule, lower IPs. Fig. 8 does not taken into account the possibility of overlap and inversion of MOs having close energies under the effects of splitting. We are not going to carry out a detailed interpretation of all features for the experimental spectra. It would take calculations of the molecules KH2PO4 and Na3PO4 using the experimental geometry. We note that the experimental spectra have three groups of peaks corresponding to transitions from MOs 3t2, le; 2t2, 2al; lt2, lal in the theoretical spectrum calculated in spd-basis. This allows us to use the calculations described above for interpretation of the experimental spectra. The symmetry decrease leads to an increase of line width, splitting and decrease of binding energy

L.N. Alexeiko, O.L. Shcheka/Journal of Electron Spectroscopy and Related Phenomena 77 (1996) 291-305

of the MOs. The first group of bands of the Na3PO 4 PL2,3 spectrum has the same shape as the theoretical (spd-basis) spectrum. But the KH2PO4 PL2,3 spectrum indicates a strong splitting of these MOs. The second group of peaks of the experimental spectrum differs strongly from the second peak shape of the theoretical spectrum. Comparing PL2,3 spectra of NaaPO4 and KH2PO4, we note that under the transition from C3v symmetry configuration to Cs symmetry configuration the strong destabilization of this group of MOs takes place. We think that these features of the KHePO4 and NaaPO 4 PL2,3 spectra are caused by transitions to the P 2p-level from MOs 4a', 5cg, 2a", 6a' and 3al, 2e, 4ch respectively. The analysis of the deeper MOs of the molecules KH2PO 4 and Na3PO 4 is not of great interest. We can note that their positions and populations are described by theoretical calculations sufficiently well. Thus, finishing the ion PO 3- electronic structure study, we note that the complicated structure of the experimental spectra and the satisfactory description by theoretical calculations in spd-basis support the hypothesis concerning the presence of the P 3d-component in the electrode density distribution for anion PO 3-.

5. Conclusion Our researches allow us to confirm that for threecoordinated phosphorus compounds the role of P 3d AOs is small. The effect of these orbitals on the electronic density distribution is of minor importance. The results of the electronic struc•ture study on the molecules PH3, P(CH3) 3 and. P(OCH3) 3 support this conclusion. On the other hand, for four-coordinated phosphorus compounds, P 3d AOs have a great affect on the electronic structure. The complicated shape of the PL2,3 spectra of the molecules OP(CH3)3, SP(CH3)3, OP(OCH3)3, Na3PO 4 and KH2PO 4 can not be explained without using the calculations in extended (spd-) basis. We note that the creation of the P 2p-vacancy

305

influences the distribution of atomic populations in valent MOs, but this effect is weak for P 3d AOs. Overall, the joint use of the X-ray emission data and SCF-X~-SW calculations allows us to estimate realistically the participation degree of the P 3d-orbitals in the valent occupied MOs of neutral phosphorus compounds.

Acknowledgements We thank Dr. Vladimir D. Yumatov for help in obtaining X-ray emission spectra and Professor Igor A. Topoi and Dr. Yury G. Abashkin for help in calculations by the SCF-X~-SW method. We also thank the editor for extensive help with the English.

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