- Email: [email protected]
Resonance raman effect of Cu3PS4 at low temperature
Vohne 59, number 1
CHEMICAL PHYSICS LETTERS
1 November 1978
RESONANCE FUMAN EFFECT OF Cu3FS4 AT LOW TEMPERATURE Maxia L.A. TEMPERINI, 0. SALA and HJ. BERNSTEIN’ IFftituzode Quhdca. Uni~Mde de So fizulo. CP_ 20780. Sno Ando,
BM.Zc
Received7 July 1978 The resonanceRaman spectraof Cu#Se at liquid nitrogen temperature, excited by sevenAr and Kr ion hse&nes, have been stlidiedand the excitationprofles comparedwith the theoreticalones. Accordingto the position of the scanered frequenciesin the absowtion band it is observedthat the relativeintensitiesof the overtonesmay or may not decreaseas the vibrationalquantummmnber increases_
1, hlhJductioll In a previous paper [l] the resonance Raman effect of solid Cu3P!Q at room temperature was reported and the experimental excitation profiles obtained, after intensity correction discussed therein It was pointed out that the fundamental and its first overt-one did not peak at the same frequency. The better signal/noise ratio at low temperature and the complete splitting of the degenerate frequencies, the sample is cocled below 200 K, allow more reliable intensity measurements to be made. In the present study the resonance Raman spectra of the Cu3PS4 at liquid nitrogen temperature were obtained and the experimental excitation profiles discussed_Considering, as an approximation, only the denominator in the Nafie et al_ formulation [2] the theoretical profiies were calculated. In order to check this approximation, the profdes obtained from the zomplete expression developed by Mingardi et al. [3] (see also refs. [4-61) have been obtained too_ The dependence of the Raman intensiries on the scattered frequency is discussed.
‘Ihe experimental arrangement and the intensity corrections, specially that due to the strong light absorption of the sample, were described elsewhere [ 1] . A conventional liquid nitrogen Raman cell was employed and a cylindrical lens used to focus the Iaser beam on the sample, to avoid heating. The spectral slit width was about 3 cm-’ for the fundamentals and 7 cm- ’ for the overtones. The band areas were measured using a planhneter.
3. Results and d.kcu&on Fig_ L shows the resonance Raman spectrum of C.3PS4 at liquid nitrogen temperature excited by
the 476.5 mu radiation. From the number of observed internal modes and the correlation diagram between the groups Td (free ion), C, (site group) and C&, (unit cell) it is possiile to see that the observed splitting is only due to the static field_ CL
Cs
=‘d
2. Exp&mentaI Cu3PS4 was prepared by heating (500°C) copper chloride with phosphorus pentasulphide as previousiy described [I]* Vi&i.n~ Professor, from Chemistry Division of National Research Council, Ottawa, Canada.
10
(6) ti In this diagram at the right are the number of internal modes for one ion, and at the left the number for two ions in the unit cell.
Volume 59, number1
I
CHE!!ICAL PHYSlCS LETTERS
I
285 c:nijC 300 320
68
a:nv,+ 106 138
“ic
,
mWCba
1 November
1978
n=5&9_..
b a I
2800
2000
too0
390
cm-’
Fig 1. ResonamzeRamanspectrumof CusPS4at liquid nitrogentemperatureexcited by 476.5 nm radiation,showingthe several progressions. The tentative assignment of the internal modes was done based on Cs symmetry, considering the observed selection rule (still consistent with that for Td) and assuming that only totally symmetric species produce a resonance Raman effect. The observed frequencies and assignments are fisted in table 1, which shows the several combinations of external and internal modes with the overtone progression in the fundamental J?S4symmetric stretching (~1). The excitation profdes represented in fig. 2 show a systematic shift to the high frequency side with ihe
increasing of the vibrational frequencies. There are only a few references about this behavior [7,S] _ This shift Can be rationalized by considering the denominator in the intensity expression given by Nafie et al. [2]_ For the Stokes bands it can be written:
=
QoQl--Qn,
(1)
where ye is the electronic absorption frequency (cm- I),
Table 1 Observedfrequencies(cm-‘) for CusPS4at iiquid nitrogentemperatureandvsignments Externalmodes: 60(O), 65sh,68(0.2), 80(1-S), 86(O), 92(O), 106~00.2), 112(0.5), 117(O),138(O),171(O),192(O),203(O), 210(O), 244(l), 326(25) <= 244 + SO) Internalmodes: A’: 285(20), 300<2),307(44).392(100), 512(3), 539(O) A”: 29Ssh,320(3) Overtonesof 392 (~1): 784,1175,1565,1953,2340,2727,3112,3499 ProgressionsinvolvingRZI~and external modesCv,,,,: Vext 68 106 138 192 203
or+ vext 462 500 528 585 595
3V1+ Vext
4W T Vext
856 889 915
1248 1278 1302
1643 1670 -
380
1370
1755
2148
2538
2vr+%nt
3vt +vint
1072 1083 1103 1302
1465 1493 1697
4VI fVint 1853 1883
Svr+vint 2245
6~1 +~int 2635 -
2% +Vext
‘5vl+ vext 2032 2058 2090
6~1s vext 2433 -
ProgressionsinvoIvinSnor and internalmodes&t): ynr 285 300 320 523
*1yVint 677 693 713 91s
2273
Infrared: 308w,321,510vs,51Svss, 523sh.539ms II
Volume59,numberl
1 November1978
CHEI(ICALPHYSICSLEl-l-ERS
I~h47_1
*c I i
1. .'20 I *
cm" ___________-
a5
-__-.__-
300
--____-
_-----
307 320
------------
392tRi 512 784<2p,l
0
, :
22000
21000
20000
79000 cm-’
Fs. 2. Excitation profiles for Cu3PSa normalized to excitation with the 647.1 MI, which is out of the resonance region_
vo is the exciting frequency, v~ is the vibrational frequency, m is the vibrationaIquantum number and l? is the damping term_ For a fundamental the fmt factor Qo, in (l), has a maximum at vo = ve and the seccnd factor Ql reaches the maximum when the scatteringfrequency vo - vR = ve_ So, the maximum of the excitation profle (QoQl) does not occur at an exciting frequency equal to v, but at a vahrebetween v, and ve f vR_ 3%~: greaterVB, the greaterwi!: be the exciting frequency of the maximumA similar argumentcan be used to justify the shift to higher frequency of the overtone profiles maxima in relation EOthe fundamental. Eq. (1) is a simple way to discuss the excitation profies. Figs. 3A and 3B show the comparison between the experimental and cakulated profties [based on eq. (l)] for three fundamentals(2283,392 and 512 cm-‘) and for the three fast overtones of 392 cm- ’ _ The best fit parametersto adjust the calculated to the experimental profiles were: ve= 20500 cm-’ and E’= 700 cm-’ for the fundamentals,and v, = 205OOcm~’ 12
cii?-’
Fs 3_ Theoretical profiles [eq. (I)] fitted to the experimental points using the indicated parameters (A and X3).The profiles C have been obtained from the e.xpmssions of ~Mingardiet al. [ 3]_
and r = 500 cm- ’ for the overtones. In the present case, K’has to be considered as the damping term of the vibronic envelope, since no vibronic structure was resolvedspectroscopically_The profiles for vl and 2~1 have also been calculated from the Mingardiet al. 133 4529
to t
\
476.5
s ; i
es.0
? : : :
u
: Y,
0 :2vs A '3v, x:4y *:5Y*
<
S 0.5.
cm” Fig_ 4_ Relative intensities of overtones to the fundamental as a function of the scattering frequencies. The exciting radiation is indicated in the correspoiding curve.
Volume 59, number 1
CHEMICAL
PHYSICS
motiel and compared with the experimental intensity
data in fig. 3C_ The best fit, to adjust the theoreticai profiles to the experimental points, gives for ve and r nearly the same values obtained from eq. (1). SO, it turns out that both rheories can be used to reproduce the data within the experimental error. The plot of overtone intensities normalized with respect to the fundamental (392 cm- I) versus the scattering frequency is presented in fig. 4, for three exciting lines. For the 457.9 nm excitation the relative intensities of the second and third overtones arc even greater than for the first overtone. This result shows that the cornrnonIy accepted idea of continuous decrease of overtone intensities as the vibrationat quantum number increases is not fulIy correct. It is valid only when the scattering frequencies of the overtones fall at the low frequency side of the absorption curve.
AcknowIedgement
LETTERS
ship for M.T. One of us (I-I_J.B.) acknowledges the financial support of the Conselho National de Desenvolvimento Cientffico e Tecnologico for his visit. Several useful discussions with W. Siebrand and A_P. Penner are gratefully acknowledged_
RefererKes III I21 131 [41 151 161 [71 [Sl
This work was supported by FundacHo de Amparo 5 Pesquisa do Estado de Sio Paulo, including a fellow-
1 h’ovemnber 1978
0_ Sala and M-LA_ Tempcrini, Chem. Phys. Letters 36 (1975) 652. L-A. Nafiq P. Stein and W.L. Peticolas, Chem. Phys. Letters 12 (1971) 131. M. Mingardi, W. Siebrand, D. van Labeke and hi. Jacon, Chem. Phys. Letters 31(1975) 208. F. Gdlhzzi, and F-F. Ricci, J. Ramar Spectry. 2 (1974) 351. F. Inagaki, M. Tasumi and T. Miyazawa, J. Mol. spectry. 50 (1974) 286. S. Sufr& G. DeUepiane, G. Masetti and G. Zerbi, J. Rarnan Spectry. 6 (1977) 267. T.G. Spiro and T-C. Strekas, Proc. Natl. Acad. Sci. US 69 (1972) 2622. T. Kamisuki, S. Mae& and H. Kobayashi, J. Rsrnan Spectry. 5 (1976) 135.
I3
CHEMICAL PHYSICS LETTERS
1 November 1978
RESONANCE FUMAN EFFECT OF Cu3FS4 AT LOW TEMPERATURE Maxia L.A. TEMPERINI, 0. SALA and HJ. BERNSTEIN’ IFftituzode Quhdca. Uni~Mde de So fizulo. CP_ 20780. Sno Ando,
BM.Zc
Received7 July 1978 The resonanceRaman spectraof Cu#Se at liquid nitrogen temperature, excited by sevenAr and Kr ion hse&nes, have been stlidiedand the excitationprofles comparedwith the theoreticalones. Accordingto the position of the scanered frequenciesin the absowtion band it is observedthat the relativeintensitiesof the overtonesmay or may not decreaseas the vibrationalquantummmnber increases_
1, hlhJductioll In a previous paper [l] the resonance Raman effect of solid Cu3P!Q at room temperature was reported and the experimental excitation profiles obtained, after intensity correction discussed therein It was pointed out that the fundamental and its first overt-one did not peak at the same frequency. The better signal/noise ratio at low temperature and the complete splitting of the degenerate frequencies, the sample is cocled below 200 K, allow more reliable intensity measurements to be made. In the present study the resonance Raman spectra of the Cu3PS4 at liquid nitrogen temperature were obtained and the experimental excitation profiles discussed_Considering, as an approximation, only the denominator in the Nafie et al_ formulation [2] the theoretical profiies were calculated. In order to check this approximation, the profdes obtained from the zomplete expression developed by Mingardi et al. [3] (see also refs. [4-61) have been obtained too_ The dependence of the Raman intensiries on the scattered frequency is discussed.
‘Ihe experimental arrangement and the intensity corrections, specially that due to the strong light absorption of the sample, were described elsewhere [ 1] . A conventional liquid nitrogen Raman cell was employed and a cylindrical lens used to focus the Iaser beam on the sample, to avoid heating. The spectral slit width was about 3 cm-’ for the fundamentals and 7 cm- ’ for the overtones. The band areas were measured using a planhneter.
3. Results and d.kcu&on Fig_ L shows the resonance Raman spectrum of C.3PS4 at liquid nitrogen temperature excited by
the 476.5 mu radiation. From the number of observed internal modes and the correlation diagram between the groups Td (free ion), C, (site group) and C&, (unit cell) it is possiile to see that the observed splitting is only due to the static field_ CL
Cs
=‘d
2. Exp&mentaI Cu3PS4 was prepared by heating (500°C) copper chloride with phosphorus pentasulphide as previousiy described [I]* Vi&i.n~ Professor, from Chemistry Division of National Research Council, Ottawa, Canada.
10
(6) ti In this diagram at the right are the number of internal modes for one ion, and at the left the number for two ions in the unit cell.
Volume 59, number1
I
CHE!!ICAL PHYSlCS LETTERS
I
285 c:nijC 300 320
68
a:nv,+ 106 138
“ic
,
mWCba
1 November
1978
n=5&9_..
b a I
2800
2000
too0
390
cm-’
Fig 1. ResonamzeRamanspectrumof CusPS4at liquid nitrogentemperatureexcited by 476.5 nm radiation,showingthe several progressions. The tentative assignment of the internal modes was done based on Cs symmetry, considering the observed selection rule (still consistent with that for Td) and assuming that only totally symmetric species produce a resonance Raman effect. The observed frequencies and assignments are fisted in table 1, which shows the several combinations of external and internal modes with the overtone progression in the fundamental J?S4symmetric stretching (~1). The excitation profdes represented in fig. 2 show a systematic shift to the high frequency side with ihe
increasing of the vibrational frequencies. There are only a few references about this behavior [7,S] _ This shift Can be rationalized by considering the denominator in the intensity expression given by Nafie et al. [2]_ For the Stokes bands it can be written:
=
QoQl--Qn,
(1)
where ye is the electronic absorption frequency (cm- I),
Table 1 Observedfrequencies(cm-‘) for CusPS4at iiquid nitrogentemperatureandvsignments Externalmodes: 60(O), 65sh,68(0.2), 80(1-S), 86(O), 92(O), 106~00.2), 112(0.5), 117(O),138(O),171(O),192(O),203(O), 210(O), 244(l), 326(25) <= 244 + SO) Internalmodes: A’: 285(20), 300<2),307(44).392(100), 512(3), 539(O) A”: 29Ssh,320(3) Overtonesof 392 (~1): 784,1175,1565,1953,2340,2727,3112,3499 ProgressionsinvolvingRZI~and external modesCv,,,,: Vext 68 106 138 192 203
or+ vext 462 500 528 585 595
3V1+ Vext
4W T Vext
856 889 915
1248 1278 1302
1643 1670 -
380
1370
1755
2148
2538
2vr+%nt
3vt +vint
1072 1083 1103 1302
1465 1493 1697
4VI fVint 1853 1883
Svr+vint 2245
6~1 +~int 2635 -
2% +Vext
‘5vl+ vext 2032 2058 2090
6~1s vext 2433 -
ProgressionsinvoIvinSnor and internalmodes&t): ynr 285 300 320 523
*1yVint 677 693 713 91s
2273
Infrared: 308w,321,510vs,51Svss, 523sh.539ms II
Volume59,numberl
1 November1978
CHEI(ICALPHYSICSLEl-l-ERS
I~h47_1
*c I i
1. .'20 I *
cm" ___________-
a5
-__-.__-
300
--____-
_-----
307 320
------------
392tRi 512 784<2p,l
0
, :
22000
21000
20000
79000 cm-’
Fs. 2. Excitation profiles for Cu3PSa normalized to excitation with the 647.1 MI, which is out of the resonance region_
vo is the exciting frequency, v~ is the vibrational frequency, m is the vibrationaIquantum number and l? is the damping term_ For a fundamental the fmt factor Qo, in (l), has a maximum at vo = ve and the seccnd factor Ql reaches the maximum when the scatteringfrequency vo - vR = ve_ So, the maximum of the excitation profle (QoQl) does not occur at an exciting frequency equal to v, but at a vahrebetween v, and ve f vR_ 3%~: greaterVB, the greaterwi!: be the exciting frequency of the maximumA similar argumentcan be used to justify the shift to higher frequency of the overtone profiles maxima in relation EOthe fundamental. Eq. (1) is a simple way to discuss the excitation profies. Figs. 3A and 3B show the comparison between the experimental and cakulated profties [based on eq. (l)] for three fundamentals(2283,392 and 512 cm-‘) and for the three fast overtones of 392 cm- ’ _ The best fit parametersto adjust the calculated to the experimental profiles were: ve= 20500 cm-’ and E’= 700 cm-’ for the fundamentals,and v, = 205OOcm~’ 12
cii?-’
Fs 3_ Theoretical profiles [eq. (I)] fitted to the experimental points using the indicated parameters (A and X3).The profiles C have been obtained from the e.xpmssions of ~Mingardiet al. [ 3]_
and r = 500 cm- ’ for the overtones. In the present case, K’has to be considered as the damping term of the vibronic envelope, since no vibronic structure was resolvedspectroscopically_The profiles for vl and 2~1 have also been calculated from the Mingardiet al. 133 4529
to t
\
476.5
s ; i
es.0
? : : :
u
: Y,
0 :2vs A '3v, x:4y *:5Y*
<
S 0.5.
cm” Fig_ 4_ Relative intensities of overtones to the fundamental as a function of the scattering frequencies. The exciting radiation is indicated in the correspoiding curve.
Volume 59, number 1
CHEMICAL
PHYSICS
motiel and compared with the experimental intensity
data in fig. 3C_ The best fit, to adjust the theoreticai profiles to the experimental points, gives for ve and r nearly the same values obtained from eq. (1). SO, it turns out that both rheories can be used to reproduce the data within the experimental error. The plot of overtone intensities normalized with respect to the fundamental (392 cm- I) versus the scattering frequency is presented in fig. 4, for three exciting lines. For the 457.9 nm excitation the relative intensities of the second and third overtones arc even greater than for the first overtone. This result shows that the cornrnonIy accepted idea of continuous decrease of overtone intensities as the vibrationat quantum number increases is not fulIy correct. It is valid only when the scattering frequencies of the overtones fall at the low frequency side of the absorption curve.
AcknowIedgement
LETTERS
ship for M.T. One of us (I-I_J.B.) acknowledges the financial support of the Conselho National de Desenvolvimento Cientffico e Tecnologico for his visit. Several useful discussions with W. Siebrand and A_P. Penner are gratefully acknowledged_
RefererKes III I21 131 [41 151 161 [71 [Sl
This work was supported by FundacHo de Amparo 5 Pesquisa do Estado de Sio Paulo, including a fellow-
1 h’ovemnber 1978
0_ Sala and M-LA_ Tempcrini, Chem. Phys. Letters 36 (1975) 652. L-A. Nafiq P. Stein and W.L. Peticolas, Chem. Phys. Letters 12 (1971) 131. M. Mingardi, W. Siebrand, D. van Labeke and hi. Jacon, Chem. Phys. Letters 31(1975) 208. F. Gdlhzzi, and F-F. Ricci, J. Ramar Spectry. 2 (1974) 351. F. Inagaki, M. Tasumi and T. Miyazawa, J. Mol. spectry. 50 (1974) 286. S. Sufr& G. DeUepiane, G. Masetti and G. Zerbi, J. Rarnan Spectry. 6 (1977) 267. T.G. Spiro and T-C. Strekas, Proc. Natl. Acad. Sci. US 69 (1972) 2622. T. Kamisuki, S. Mae& and H. Kobayashi, J. Rsrnan Spectry. 5 (1976) 135.
I3