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The vacuum ultraviolet spectra of fluorine chlorine substituted trivalent phosphorus
Volume 18, number 3
.1 Febrwary 1973
CHEMICAL PHYSICS LETTERS
THE VACUUM ULTRAVIOLET SPECTRA OF FLUORINE CHLORINE SUBSTITUTED TRIVALENT PHOSPHORUS _ ‘w-yJaneMcADAMS and B.R. RUSSELL Molecular
Smctuie
Group, Department
of Chemimy,
North
Texas Sfate University, Demon.
Received 11 July 1972 Revised manuscript received 7 November
Texas 76203,
USA
1972
The vapor phase absorption spectra of PF 3, PFzCI, PFC12, and PC13 are reported in the vacuum ultraviolet spectral regicn 2400-1200 A. These results are compared with information obtained from photoelectron spectra. A brief discussion of the spectra in terms of analogous absorption regions and results from CND0/2 calculations are given.
Only limited studies have been made of the vacuum ultraviolet (VUV) absorption spectra of phosphorus (III) halides. Humphries et al. [ 1J earlier reported the spectra of PCI, from 2000-1300 8, and PF, from ISOO-1050 A. Absorprion bands containing vibrational structure in the two compounds were discussed in regard to the geometries of the excited states. Halmann [2] reported the spectra of PCI, from 2500-1860 a and later Holden [3] considered the spectra of PF, and PCI, in the region 2400-1200 8. In an effort to understand the eiectronic structure, the VUV absorption spectra corresponding to the sequential change of a fluorine atom in PF3 by a chlorine atom to PC13 was expected to provide insight into the changes of energies of the nonbonding electrons on the phosphorus atom.
The spectra were obtained using a McPherson FS-spectrophotometer which has been described elsewhere [4]. The pressure readings were made with CEC “autovac” gauge, which had been previously calibrated in the pressure range with a McLeod gauge for each gas. The PF, and PCI, were obtained commercially from Peninsular Chemresearch and Matheson, Coleman and Bell, respectively, and were purified by vacuum distillation. The’PF2C1 and PFC12 were prepared using the method described by Holmes and Gallagher [S]. These compounds were separated by means of a series of slushes and were stored in liquid nitrogen until the spectra :were taken. The separation of these two 255
compounds is extremely difficult as noted by Pan-y and coworkers[6]; thus, the purity of the mived halide compounds is estimated to be 95% or better. The purity was detarmined by mass spectral data and comparison of the VUV absorptions for the four compounds considered. The absorption spectra of the four compounds are given in fig. I. The spectral data are summarized in table 1, where band maxima, molar absorptivities, and oscillator strengths are tabulated for the four compounds. The average vibrational spacing for the structured bands in PF, and PCI, agree with the values reported by Humphries et al. and are given in table 2. For comparison purposes -he photoelectron and IR data [7, 81 are also included. The similarity of the structured bands in the photoelectron spectra reported by Potts [9] and later by Turner [IO] indicates that the exited state and the ion are possibly similar. The excited state was predicted to be planar by Walsh [ 1 I] from theoretical considerations; however the interpretation of the structured absorption band by Humphries et al. indicated that ‘Lheexcited state was not planar [I]_ Since the ion and the Rydberg state are probably similar, eNDO,’ calculations [ 121 were made to determine the predicted configuration for the PF, ion. The results of the calculation for the ion indicate the planar form is the most stable. Thus, the result for the ion suggests that the Rydberg state is also planar. Assuming that this structured band jn PF, is the first mem-
CHEMICAL PHYSICS LETTERS
Volume 18, number 3
Table 1 Band maxima, molar absorptivities and oscillator strength of PC13, PCI1,F, PCIFz and PF3 Band mas (cm-‘) ~.__._
Emax
Oscjlfator strength
._--_-_-_~___
PC13
46 48 57 66 70 73 19
000 750 100 500 000 500 700
6 720 5 440 8 000 20 900 7 280 59 400 s2 000
0.10 0.07 0.28 0.48 0.06 0.62 0.64
PCIz F
48 750 53 000 57 350 71700 72 300 7.5 500 80 000
3 580 3 740 4 130 7 850 8 020 3 580 14 500
0.05 0.04 0.10
PC1F*
48 500 54 500 58 100 66 700 70 300 7.5 800 80 200
496 2 120 7 620 4 250 3 740 6 300 9 150
0.01 0.03 0.11 0.11 0.04 0.17 0.20
PF3
63 800 66 100 76 900
14 630 14 100 5 650
0.28 0.20 0.28
UNITS
ajIl_
r=
Table 2
PC13 PF3 --
--
261 460
----_
CM“ 50
0.04 0.41
ber in a Rydberg series, and since the ionization pctential for the electron is known from photoelectron spectra [13], the effective quantum number is 2.2, However, little can be deduced from this value, as the lowest member of a Rydberg series is expected to undergo considerable molecular involvement. The effective quantum number of the analogous band in PC13 is 2.5, A comparison of the electronic spectra for the series of compounds indicates that the presence of a chlorine atom adds significantly to the complexit), of the spec-
WV
1000
0.34
I
---
“,‘o
70
1973
I
1200
Vibrational separations in cm-’ and IR (symmetrical bend) ___-
i February
from VUV, photoelectron,
PEPI
IR
250
260 171
so0
487 [El
...._._._ __..I
1400
7600
-2
1800
WAVELENGTH
2000
2200
24M)
(ii,
Fig. 1. The vacuum ultraviolet spectra of PF3, PFaCl. PFCI, ,. and PC13 at 90 microns pressure. The &shed line corresponds to the instrumental baseline.
tra for the region investigated. The spectrum of PF, has only two principal absorption regions while the spectra of the chlorine containing molecules have several additional absorptions. In addition, the oscifiator strengths of these new absorpiions vary proportionally to the I?umber of chlorine atoms present. The nonbonding electrons on the phosphorus atom are affected by the substituents [3] and transitions which involve these electrons are expecfed .to vary in accordance to the partial positive charge on the phosphorus atom. Therefore the absorptions in the spectrum of PF3 are expected to be shifted to lower energy as the fluorine atoms are replaced by the cNorine atoms. This trend is observed, see fig. 2, specificaIIy for the first absorption in PC& and the second absorption in
..
403’
Volume 18, number 3
CHEMICAL PHYSICS LETTERS At-4
“Cl
.53
pF3 pF*Cl
_--_.*. .14
!
,*3!_.-jIi;LL,r
I’ ,391
221
.45/1 /,’ 8’
.6&’
PFCiz
,’
50 Fig. 2. Transition
,““I””
55 60 ENERGY
’ ““/““I”65 70 3 CMio
energies and transition
momcnt
75
lengths.
l.February
1973
maxima for the two Cgv molecules as arising from static Jahr-Teller distortion. Since PF, (C,,) is a non-
linear molecule which has a degenerate electronic state, vibronk coupling could occur to Iower the symmetry to C, and remove the degeneracy. The assignment of a Jahn-TeLler split in the 15.50 A band is reasonable, since Jahn-Teller splittings have been observed in the photoelectron spectra of a degenerate state in similar simple molecules [ 10, 161. The authors gratefully acknowledge helpful discussions wirh J.D. Scott and financial support from the Robert A. Welch Foundation, Research Corporation, and NTSU Faculty Research.
Table 3.
ionization potentials in eV from photoelectron spectra _-_.---.-----..----.-. --------1st I 2nd 3rd Ref.
---
References
- -.-...... __--.--___.________
12.3 (VP) 15.6 (nF) PF3 PF*Cl 11.5 (nCl) 12.S (nP) PFCIZa) PC13 10.5 (I#) 11.71(nC1) _I--.-.. ---..--.----.a) Not available.
16.3 (P-F)
1131
15.7 (P-Cl)
(141
1’.01(P-c1) --..--. ______ [ 91
PC12F and PCIF,. These transitions are tentatively assigned to the nonbonding electrons on phosphorus. This is also true for the bands originating at 56 000 cm-1 ax! 66 000 cm-l with PC13 as plotted in fig. 2. The 48 000 cm-l band remains at approximately the same energy in the chlorine containing compounds. Thus, this transition is tentatively assigned as a nonbonding chlorine electron going to a u” orbital, O*P-cI + “Cl* Results from photoelectron spectra [14] substantiate the assignment that the first eiectron arises from a chlorine in PFZC1. The first three ionization poteniials for three of the compounds are given in table 3. The sharp band at 1290 A in the PF,CI spectrum is attributed to MCI [ 151 in the system, since
its intensity varied irregularly with pressure. Fig. 2 coma&s the principal absorption maxima for the four compounds,, the dotted,lines connect the respective absorption maxima corresponding to the variations as the molecular symmetry is varied. Previously, Holder. [3] had assigned specific absorption
[ 1 ] C.&I. Humphries, A.D. Walsh and P.A. Warsop, Discussions Faraday Sot. 35 (1963) 148. 121 hI. Halmann, J. Chem. Sot. (1963) 2853. [3] M.P. Holden. Doctoral Dissertation, University of Washington (1966). [4] J.D. Scott and B.R. Russell, J. Am. Chem. Sot. 94 (1972) 2634. IS] R.R. Holmes and W.P. Gallagher, Inorg. Chem. 2 (1963) 433. 161 J.G. Morse, K. Cohn, R.W. Rudolph and R.W. Parry, Inorganic Synthesis 10 (1971) 147. i7] P.W. Da\.is and R.A. Oetyen, J. Mol. Spectry. 2 (1958) 253. [S] M.K. Wilson and R. Polo, J. Chem. Phys. 20 (1952) 1716. [9] A.W. Pot!s, H.J. Lempka, D.G. Streets and W.C. Price, Phil. Trans. Roy. Sot. London 268 (1970) 69. [IO] J.P. hiaier and D.W. Turner, J. Chem. Sot. Faraday Trans. II (1972) 711. [ll] A.D. WJsh, J. Chem. Sot. (1953) 2301. [ 121 J.A. Pople and D.L. Beveridge, Approsimatc molecular orbital theory (McGraw-Hill, New York, 1970) ch. 4; P.A. Kolim3n and L.C. Allen, Chem. Rev. 72 (1972) 283. [13j P.J. Bassett, D-R. Lloyd, I.H. Hillier and V.R. Saunders, Chem. Phys. Letters 6 (1970) 253. [ 141 S. Cradock and D.W. H. Rankin, J. Chem. Sot. Faraday Trans. II (1972) 940. [ 15 J A.J. hlye: and J.A.R. Samson, J. Chem. Phys. 52 (1970) 226. 1161 J.W. Rab!ais, T. Bergmark, L.O. Werme, L:Karlsson and, K,Siegbahn. Physica Scripta 3 (1971) 13.
.1 Febrwary 1973
CHEMICAL PHYSICS LETTERS
THE VACUUM ULTRAVIOLET SPECTRA OF FLUORINE CHLORINE SUBSTITUTED TRIVALENT PHOSPHORUS _ ‘w-yJaneMcADAMS and B.R. RUSSELL Molecular
Smctuie
Group, Department
of Chemimy,
North
Texas Sfate University, Demon.
Received 11 July 1972 Revised manuscript received 7 November
Texas 76203,
USA
1972
The vapor phase absorption spectra of PF 3, PFzCI, PFC12, and PC13 are reported in the vacuum ultraviolet spectral regicn 2400-1200 A. These results are compared with information obtained from photoelectron spectra. A brief discussion of the spectra in terms of analogous absorption regions and results from CND0/2 calculations are given.
Only limited studies have been made of the vacuum ultraviolet (VUV) absorption spectra of phosphorus (III) halides. Humphries et al. [ 1J earlier reported the spectra of PCI, from 2000-1300 8, and PF, from ISOO-1050 A. Absorprion bands containing vibrational structure in the two compounds were discussed in regard to the geometries of the excited states. Halmann [2] reported the spectra of PCI, from 2500-1860 a and later Holden [3] considered the spectra of PF, and PCI, in the region 2400-1200 8. In an effort to understand the eiectronic structure, the VUV absorption spectra corresponding to the sequential change of a fluorine atom in PF3 by a chlorine atom to PC13 was expected to provide insight into the changes of energies of the nonbonding electrons on the phosphorus atom.
The spectra were obtained using a McPherson FS-spectrophotometer which has been described elsewhere [4]. The pressure readings were made with CEC “autovac” gauge, which had been previously calibrated in the pressure range with a McLeod gauge for each gas. The PF, and PCI, were obtained commercially from Peninsular Chemresearch and Matheson, Coleman and Bell, respectively, and were purified by vacuum distillation. The’PF2C1 and PFC12 were prepared using the method described by Holmes and Gallagher [S]. These compounds were separated by means of a series of slushes and were stored in liquid nitrogen until the spectra :were taken. The separation of these two 255
compounds is extremely difficult as noted by Pan-y and coworkers[6]; thus, the purity of the mived halide compounds is estimated to be 95% or better. The purity was detarmined by mass spectral data and comparison of the VUV absorptions for the four compounds considered. The absorption spectra of the four compounds are given in fig. I. The spectral data are summarized in table 1, where band maxima, molar absorptivities, and oscillator strengths are tabulated for the four compounds. The average vibrational spacing for the structured bands in PF, and PCI, agree with the values reported by Humphries et al. and are given in table 2. For comparison purposes -he photoelectron and IR data [7, 81 are also included. The similarity of the structured bands in the photoelectron spectra reported by Potts [9] and later by Turner [IO] indicates that the exited state and the ion are possibly similar. The excited state was predicted to be planar by Walsh [ 1 I] from theoretical considerations; however the interpretation of the structured absorption band by Humphries et al. indicated that ‘Lheexcited state was not planar [I]_ Since the ion and the Rydberg state are probably similar, eNDO,’ calculations [ 121 were made to determine the predicted configuration for the PF, ion. The results of the calculation for the ion indicate the planar form is the most stable. Thus, the result for the ion suggests that the Rydberg state is also planar. Assuming that this structured band jn PF, is the first mem-
CHEMICAL PHYSICS LETTERS
Volume 18, number 3
Table 1 Band maxima, molar absorptivities and oscillator strength of PC13, PCI1,F, PCIFz and PF3 Band mas (cm-‘) ~.__._
Emax
Oscjlfator strength
._--_-_-_~___
PC13
46 48 57 66 70 73 19
000 750 100 500 000 500 700
6 720 5 440 8 000 20 900 7 280 59 400 s2 000
0.10 0.07 0.28 0.48 0.06 0.62 0.64
PCIz F
48 750 53 000 57 350 71700 72 300 7.5 500 80 000
3 580 3 740 4 130 7 850 8 020 3 580 14 500
0.05 0.04 0.10
PC1F*
48 500 54 500 58 100 66 700 70 300 7.5 800 80 200
496 2 120 7 620 4 250 3 740 6 300 9 150
0.01 0.03 0.11 0.11 0.04 0.17 0.20
PF3
63 800 66 100 76 900
14 630 14 100 5 650
0.28 0.20 0.28
UNITS
ajIl_
r=
Table 2
PC13 PF3 --
--
261 460
----_
CM“ 50
0.04 0.41
ber in a Rydberg series, and since the ionization pctential for the electron is known from photoelectron spectra [13], the effective quantum number is 2.2, However, little can be deduced from this value, as the lowest member of a Rydberg series is expected to undergo considerable molecular involvement. The effective quantum number of the analogous band in PC13 is 2.5, A comparison of the electronic spectra for the series of compounds indicates that the presence of a chlorine atom adds significantly to the complexit), of the spec-
WV
1000
0.34
I
---
“,‘o
70
1973
I
1200
Vibrational separations in cm-’ and IR (symmetrical bend) ___-
i February
from VUV, photoelectron,
PEPI
IR
250
260 171
so0
487 [El
...._._._ __..I
1400
7600
-2
1800
WAVELENGTH
2000
2200
24M)
(ii,
Fig. 1. The vacuum ultraviolet spectra of PF3, PFaCl. PFCI, ,. and PC13 at 90 microns pressure. The &shed line corresponds to the instrumental baseline.
tra for the region investigated. The spectrum of PF, has only two principal absorption regions while the spectra of the chlorine containing molecules have several additional absorptions. In addition, the oscifiator strengths of these new absorpiions vary proportionally to the I?umber of chlorine atoms present. The nonbonding electrons on the phosphorus atom are affected by the substituents [3] and transitions which involve these electrons are expecfed .to vary in accordance to the partial positive charge on the phosphorus atom. Therefore the absorptions in the spectrum of PF3 are expected to be shifted to lower energy as the fluorine atoms are replaced by the cNorine atoms. This trend is observed, see fig. 2, specificaIIy for the first absorption in PC& and the second absorption in
..
403’
Volume 18, number 3
CHEMICAL PHYSICS LETTERS At-4
“Cl
.53
pF3 pF*Cl
_--_.*. .14
!
,*3!_.-jIi;LL,r
I’ ,391
221
.45/1 /,’ 8’
.6&’
PFCiz
,’
50 Fig. 2. Transition
,““I””
55 60 ENERGY
’ ““/““I”65 70 3 CMio
energies and transition
momcnt
75
lengths.
l.February
1973
maxima for the two Cgv molecules as arising from static Jahr-Teller distortion. Since PF, (C,,) is a non-
linear molecule which has a degenerate electronic state, vibronk coupling could occur to Iower the symmetry to C, and remove the degeneracy. The assignment of a Jahn-TeLler split in the 15.50 A band is reasonable, since Jahn-Teller splittings have been observed in the photoelectron spectra of a degenerate state in similar simple molecules [ 10, 161. The authors gratefully acknowledge helpful discussions wirh J.D. Scott and financial support from the Robert A. Welch Foundation, Research Corporation, and NTSU Faculty Research.
Table 3.
ionization potentials in eV from photoelectron spectra _-_.---.-----..----.-. --------1st I 2nd 3rd Ref.
---
References
- -.-...... __--.--___.________
12.3 (VP) 15.6 (nF) PF3 PF*Cl 11.5 (nCl) 12.S (nP) PFCIZa) PC13 10.5 (I#) 11.71(nC1) _I--.-.. ---..--.----.a) Not available.
16.3 (P-F)
1131
15.7 (P-Cl)
(141
1’.01(P-c1) --..--. ______ [ 91
PC12F and PCIF,. These transitions are tentatively assigned to the nonbonding electrons on phosphorus. This is also true for the bands originating at 56 000 cm-1 ax! 66 000 cm-l with PC13 as plotted in fig. 2. The 48 000 cm-l band remains at approximately the same energy in the chlorine containing compounds. Thus, this transition is tentatively assigned as a nonbonding chlorine electron going to a u” orbital, O*P-cI + “Cl* Results from photoelectron spectra [14] substantiate the assignment that the first eiectron arises from a chlorine in PFZC1. The first three ionization poteniials for three of the compounds are given in table 3. The sharp band at 1290 A in the PF,CI spectrum is attributed to MCI [ 151 in the system, since
its intensity varied irregularly with pressure. Fig. 2 coma&s the principal absorption maxima for the four compounds,, the dotted,lines connect the respective absorption maxima corresponding to the variations as the molecular symmetry is varied. Previously, Holder. [3] had assigned specific absorption
[ 1 ] C.&I. Humphries, A.D. Walsh and P.A. Warsop, Discussions Faraday Sot. 35 (1963) 148. 121 hI. Halmann, J. Chem. Sot. (1963) 2853. [3] M.P. Holden. Doctoral Dissertation, University of Washington (1966). [4] J.D. Scott and B.R. Russell, J. Am. Chem. Sot. 94 (1972) 2634. IS] R.R. Holmes and W.P. Gallagher, Inorg. Chem. 2 (1963) 433. 161 J.G. Morse, K. Cohn, R.W. Rudolph and R.W. Parry, Inorganic Synthesis 10 (1971) 147. i7] P.W. Da\.is and R.A. Oetyen, J. Mol. Spectry. 2 (1958) 253. [S] M.K. Wilson and R. Polo, J. Chem. Phys. 20 (1952) 1716. [9] A.W. Pot!s, H.J. Lempka, D.G. Streets and W.C. Price, Phil. Trans. Roy. Sot. London 268 (1970) 69. [IO] J.P. hiaier and D.W. Turner, J. Chem. Sot. Faraday Trans. II (1972) 711. [ll] A.D. WJsh, J. Chem. Sot. (1953) 2301. [ 121 J.A. Pople and D.L. Beveridge, Approsimatc molecular orbital theory (McGraw-Hill, New York, 1970) ch. 4; P.A. Kolim3n and L.C. Allen, Chem. Rev. 72 (1972) 283. [13j P.J. Bassett, D-R. Lloyd, I.H. Hillier and V.R. Saunders, Chem. Phys. Letters 6 (1970) 253. [ 141 S. Cradock and D.W. H. Rankin, J. Chem. Sot. Faraday Trans. II (1972) 940. [ 15 J A.J. hlye: and J.A.R. Samson, J. Chem. Phys. 52 (1970) 226. 1161 J.W. Rab!ais, T. Bergmark, L.O. Werme, L:Karlsson and, K,Siegbahn. Physica Scripta 3 (1971) 13.