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Re-examination of electronic chemiluminescence from TiO
JOURN.\L
OF
MOLI~(‘ULIH
SPF:CTROSCOPI-
43, 32(t-322 (1972)
NOTES
Re-examination
of Electronic
Chemiluminescence
from
TiO’
Pathak and Palmer (1) observed the emission spectrum from the reaction of TiCL with potassium vapor at low pressure and temperature in the presence of added oxygen. The spectra were recorded at low resolution (ca. 1 A). In addition to known visible bands of TiO, they ident’ified four ultraviolet band systems, all of which were assigned to TiO. A continuum prevented identification of bands in the region between 3980 and 4420 A.. The most prominent feature of the ultraviolet region was a complex collection of bands iu the region 2900-3260 A. that were attributed to a triplet-triplet transition, D-S3A, , with the new D state lying in the vicinity of 32 000 cm-‘. A progression of weak double-headed bands was found between 3286 and 3650 i and two sequences were observed: 3488-3545 A and 3757-3820 A. The last two systems were observed only under special conditions of relatively high pressure in the reaction vessel and were very difficult to obtain. Furthermore, they were not observed when TiBr4 was substituted for TiC14. Nevertheless, these systems were also assigned to TiO because they were obviously diatomic and no other species seemed possible as an emitter of the bands. The D-X system has recently found support in the matrix-trapping study of TiO by McIntyre, Thompson, and Weltner (2). We have now rest,udied the gas-phase emission nnder conditions essentially identical to those employed by Pathak and Palmer, but using NsO rather than 02 as the oxygen-containing additive. The observations confirm the 29OG 3260 _&emission and also the weak bands between 3286 and 3650 d.. It has not been possible to see the bands at 3488-3545 d and 37573820 b. The reason for this has now become evident after a search of the literature that was stimulated by the critical appraisal of the spectra of TiO, H,fO, and ThO cacried out by Wentink and Spindler (3). The 3488-3545 A and 37573820 A bands are impurity bands due to SnCl. A comparison is presented in Table I. The Tic14 (Fisher “Purified” grade) must have contained enough SnClc to give excitation of SnCl by energy transfer from TiO when the pressure was relatively high. Production of excited SnCl at the energy required (276 kcal) by Ii atoms stripping off the halogen atoms from SnC14 seems unlikely. The finding of Sn as au impurity has prompted us to investigate SnO as a possible emitter of the two remaining systems that are still attributed to TiO. The known SnO bands (4) do not fit the observations, although some of the transitions lie in the same general region as the TiO bands. Because of the latter point, we doubt that we could be exciting new SnO bands in this region without also exciting known systems. A comparison of the present study of emission from the chemical system TiC14-K-N20 with the emission reported by Pathak and Palmer is presented in Table II. The present measurements were made without reference to the previous work. As in that work, a large number of known TiO bands in the visible were found, and a number of new bands belonging to known systems. These are not tabulated, but are mentioned to emphasize the fact that we are seeing electronic emission from TiO. In general, the present observations agree with the previous ones to within the nncer1 Work
supported
by
the National
Science 320
Copyright @ 1972 hy Academic Press, Inc. All rights of reproduction in any form reserved.
Foundation.
NOTES TABLE
321 I
ATTRIBUTIONOF IMPURITY BANDS TO SnCl (aA-aII) X[obsd (I)]@,
3765 3769 3778 3775 1 3785
air)
X[obsd (I)](&
air)
a’, V”
3758.5
0,o i
3488
3487.8
0,O ii
3767.3
1,l
i
3496
3494.7
1,l
3776.6
2,2 i
3503
3502.5
2,2 ii
2786.3
3,3 i
3512
3511.2
3,3 ii
TABLE
h[lit. (d)]
&H
X[lit. ($1
ii
II
COMPARISON OF ULTR.\VIOLETTiO BANDS IN THE REGION 3ooO-3650 A FROM THE PRESENT STUDY .IND TH.~T OF PATHAK AND PALMER (1) Obsd x,i& 3646 3521 3407 3295 3244 3216 3198 3149 3142 3118
3071 3049 3022
Identification
Ref. (1) X,ir(A) 3642 3635 3519 3512 3402 3396 3292 I 3286 3251 3244 3218 3215
I
3148 3142 3117 3114 3090 3084 3069 3062 3049 3043 3019 3015 3006
(0,3)
l)ouble-headed
(0,2)
l>ouble-headed
(0,l)
llouhle-headed
(0,O) Double-headed (0,l) O-FA, (0,l) D-SSA, (0,l) D-X3A, (0,l) D-X3A, Unclassified (0,O) D-PA, (0,O) D-53A, (0,O) D-PA, (0,O) D-X”A, Unclassified Unclassified Unclassified Unclassified (1,O) D-PA, (1,O) D-PA, (1,O) D-S3A, (1,0) D-PA, Unclassified
tainties associated with measurements in the two studies. The poorest agreement occurs in the double-headed 3286-3650 A. progression. The bands were so weak that the second head, which was just discernible by eye, could not be measured. The uncert,ainty in the stronger head is undoubtedly larger than in the previous study.
NOTES
322
Our new measurements clearly support the D-S system, but some of the previously measured heads have not been picked out from the complicated array of bands. A vibrat,ional analysis based solely upon the present measuremenbs might be difficult; however, with the exception of t,hree unclassified bands, two of which were also reported by Pathak and Palmer, all of our measured *ads fit into their scheme. With the reinforcement provided by the assignment of 3117.5 A to the (0,O) transition in the matrix work @), we believe the essential correctness of the D-S assignment is reasonably well established. The average of the (0,O) bands put,s t,he energy of the D state very close to 32 000 cm-‘, as found before (1). The situation with regard to the double-headed bands is not at all clear. There is no assurance that the (0,O) band is correctly assigned; in fact, age can conceive that the progression mighkinclude the unassigned bands at 3198 and 3093 A and perhaps the unassigned band at 2992 A from Pathak and Palmer’s work. The uncertainties in these weak band:, several of which fall in the midst of t,he confusion of the D-S system, are probably 2 or 3 A. It is just barely possible that the (0,O) band could lie at about 31 300 cm-1 and the system could be a progression D-U’A. The weakness of the bands would support the forbiddenness, while at the same time the fact that they are seen lends appeal to the postulate that the same upper state is responsible for them as for the D-X bands. The double heads could, of course, be an artifact of the low resolution. The answer to this suggestion can only emerge from work of higher precision. ACKNOWLEDGMENTS We want to acknowledge some computational help from A. K. Brienza. We are particularly indebted to Dr. Tunis Wentink for his correspondence and for an advance copy ofihis paper (3).
RECEIVED: March
24,1972. REFERENCES
i. &. S. 4.
C. M. PATHOS .~ND H. B. PALMER, J. Mol. Spectrosc. 33, 137 (1970). N. S. ~%INTYRE, K. R. THOMPSON,.&NDW. WELTNER, JR., J. Phys. Chem. 76,3243 T. WENTINK, JR. AND R. J. SPINDLER, JR., submitted to J. Mol. Spectrosc. of Molecular As cited in R. W. B. PEARSE AND A. G. GAYDON, I‘ The Identificat,ion tra,” 3rd ed., Chapman and Hall, London, 1963.
Fuel Science Section, Department Pennsylvania State University, University Park, Pennsylvania
of Material
Sciences,
(1971). Spec-
H. B. PALMER AND C. J. Hsu
OF
MOLI~(‘ULIH
SPF:CTROSCOPI-
43, 32(t-322 (1972)
NOTES
Re-examination
of Electronic
Chemiluminescence
from
TiO’
Pathak and Palmer (1) observed the emission spectrum from the reaction of TiCL with potassium vapor at low pressure and temperature in the presence of added oxygen. The spectra were recorded at low resolution (ca. 1 A). In addition to known visible bands of TiO, they ident’ified four ultraviolet band systems, all of which were assigned to TiO. A continuum prevented identification of bands in the region between 3980 and 4420 A.. The most prominent feature of the ultraviolet region was a complex collection of bands iu the region 2900-3260 A. that were attributed to a triplet-triplet transition, D-S3A, , with the new D state lying in the vicinity of 32 000 cm-‘. A progression of weak double-headed bands was found between 3286 and 3650 i and two sequences were observed: 3488-3545 A and 3757-3820 A. The last two systems were observed only under special conditions of relatively high pressure in the reaction vessel and were very difficult to obtain. Furthermore, they were not observed when TiBr4 was substituted for TiC14. Nevertheless, these systems were also assigned to TiO because they were obviously diatomic and no other species seemed possible as an emitter of the bands. The D-X system has recently found support in the matrix-trapping study of TiO by McIntyre, Thompson, and Weltner (2). We have now rest,udied the gas-phase emission nnder conditions essentially identical to those employed by Pathak and Palmer, but using NsO rather than 02 as the oxygen-containing additive. The observations confirm the 29OG 3260 _&emission and also the weak bands between 3286 and 3650 d.. It has not been possible to see the bands at 3488-3545 d and 37573820 b. The reason for this has now become evident after a search of the literature that was stimulated by the critical appraisal of the spectra of TiO, H,fO, and ThO cacried out by Wentink and Spindler (3). The 3488-3545 A and 37573820 A bands are impurity bands due to SnCl. A comparison is presented in Table I. The Tic14 (Fisher “Purified” grade) must have contained enough SnClc to give excitation of SnCl by energy transfer from TiO when the pressure was relatively high. Production of excited SnCl at the energy required (276 kcal) by Ii atoms stripping off the halogen atoms from SnC14 seems unlikely. The finding of Sn as au impurity has prompted us to investigate SnO as a possible emitter of the two remaining systems that are still attributed to TiO. The known SnO bands (4) do not fit the observations, although some of the transitions lie in the same general region as the TiO bands. Because of the latter point, we doubt that we could be exciting new SnO bands in this region without also exciting known systems. A comparison of the present study of emission from the chemical system TiC14-K-N20 with the emission reported by Pathak and Palmer is presented in Table II. The present measurements were made without reference to the previous work. As in that work, a large number of known TiO bands in the visible were found, and a number of new bands belonging to known systems. These are not tabulated, but are mentioned to emphasize the fact that we are seeing electronic emission from TiO. In general, the present observations agree with the previous ones to within the nncer1 Work
supported
by
the National
Science 320
Copyright @ 1972 hy Academic Press, Inc. All rights of reproduction in any form reserved.
Foundation.
NOTES TABLE
321 I
ATTRIBUTIONOF IMPURITY BANDS TO SnCl (aA-aII) X[obsd (I)]@,
3765 3769 3778 3775 1 3785
air)
X[obsd (I)](&
air)
a’, V”
3758.5
0,o i
3488
3487.8
0,O ii
3767.3
1,l
i
3496
3494.7
1,l
3776.6
2,2 i
3503
3502.5
2,2 ii
2786.3
3,3 i
3512
3511.2
3,3 ii
TABLE
h[lit. (d)]
&H
X[lit. ($1
ii
II
COMPARISON OF ULTR.\VIOLETTiO BANDS IN THE REGION 3ooO-3650 A FROM THE PRESENT STUDY .IND TH.~T OF PATHAK AND PALMER (1) Obsd x,i& 3646 3521 3407 3295 3244 3216 3198 3149 3142 3118
3071 3049 3022
Identification
Ref. (1) X,ir(A) 3642 3635 3519 3512 3402 3396 3292 I 3286 3251 3244 3218 3215
I
3148 3142 3117 3114 3090 3084 3069 3062 3049 3043 3019 3015 3006
(0,3)
l)ouble-headed
(0,2)
l>ouble-headed
(0,l)
llouhle-headed
(0,O) Double-headed (0,l) O-FA, (0,l) D-SSA, (0,l) D-X3A, (0,l) D-X3A, Unclassified (0,O) D-PA, (0,O) D-53A, (0,O) D-PA, (0,O) D-X”A, Unclassified Unclassified Unclassified Unclassified (1,O) D-PA, (1,O) D-PA, (1,O) D-S3A, (1,0) D-PA, Unclassified
tainties associated with measurements in the two studies. The poorest agreement occurs in the double-headed 3286-3650 A. progression. The bands were so weak that the second head, which was just discernible by eye, could not be measured. The uncert,ainty in the stronger head is undoubtedly larger than in the previous study.
NOTES
322
Our new measurements clearly support the D-S system, but some of the previously measured heads have not been picked out from the complicated array of bands. A vibrat,ional analysis based solely upon the present measuremenbs might be difficult; however, with the exception of t,hree unclassified bands, two of which were also reported by Pathak and Palmer, all of our measured *ads fit into their scheme. With the reinforcement provided by the assignment of 3117.5 A to the (0,O) transition in the matrix work @), we believe the essential correctness of the D-S assignment is reasonably well established. The average of the (0,O) bands put,s t,he energy of the D state very close to 32 000 cm-‘, as found before (1). The situation with regard to the double-headed bands is not at all clear. There is no assurance that the (0,O) band is correctly assigned; in fact, age can conceive that the progression mighkinclude the unassigned bands at 3198 and 3093 A and perhaps the unassigned band at 2992 A from Pathak and Palmer’s work. The uncertainties in these weak band:, several of which fall in the midst of t,he confusion of the D-S system, are probably 2 or 3 A. It is just barely possible that the (0,O) band could lie at about 31 300 cm-1 and the system could be a progression D-U’A. The weakness of the bands would support the forbiddenness, while at the same time the fact that they are seen lends appeal to the postulate that the same upper state is responsible for them as for the D-X bands. The double heads could, of course, be an artifact of the low resolution. The answer to this suggestion can only emerge from work of higher precision. ACKNOWLEDGMENTS We want to acknowledge some computational help from A. K. Brienza. We are particularly indebted to Dr. Tunis Wentink for his correspondence and for an advance copy ofihis paper (3).
RECEIVED: March
24,1972. REFERENCES
i. &. S. 4.
C. M. PATHOS .~ND H. B. PALMER, J. Mol. Spectrosc. 33, 137 (1970). N. S. ~%INTYRE, K. R. THOMPSON,.&NDW. WELTNER, JR., J. Phys. Chem. 76,3243 T. WENTINK, JR. AND R. J. SPINDLER, JR., submitted to J. Mol. Spectrosc. of Molecular As cited in R. W. B. PEARSE AND A. G. GAYDON, I‘ The Identificat,ion tra,” 3rd ed., Chapman and Hall, London, 1963.
Fuel Science Section, Department Pennsylvania State University, University Park, Pennsylvania
of Material
Sciences,
(1971). Spec-
H. B. PALMER AND C. J. Hsu