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The far and vacuum ultraviolet spectrum of SeO
JOURNAL
OF MOLECULAR
SPECTROSCOPY
The Far and
Vacuum
13, 168-173 (1964)
Ultraviolet
Spectrum
of Se0
P. B. V. HARANATH Physics
Department,
Andhra
University, Waltair, India
Four violet degraded band systems C-S, D-x, E-X, and F-x observed in the region X2400-X1800have been newly identified in the emission spectrum of the Se0 molecule excited in an rf discharge. For three of these systems the following vibrational constants in cm-i are derived from the analysis. System C-Iy
D-x F-x
Ye
50,862 46,023 47,807
X,‘W,’
We
1034.o 942.0 970.0
6.0 3.5 6.0
we
I,
915.0 880.0 880.0
x e“co P”
4.5 5.0 5.0
Bands belonging to the E-S system form a single ground-state progression. The lower state z common to D-x and F-x systems is different from the ground state X(W) of the Se0 molecule and is identified as the %+ state arising from the same configuration. Probable electronic transitions responsible for the emission of the four systems have been suggested. INTRODUCTION The emission spectrum of Se0 studied thus far reveals only a number of double headed red degraded bands extending from X3900-X2900. Barrow and Deutsch (1) assigned them to a single system of 3Z--3X- transition similar to the Schumann-Runge band system of oxygen. Recent studies of the emission spectrum of sulfur by Tanaka and Ogawa (2) and by the author (3) have led to the analysis and identification of a number of discrete band systems in the far and vacuum ultraviolet regions. This work has suggested the possibility of the occurrence of similar systems in the spectra of the other homologous molecules of this oxygen group. The present investigation carried out by the author on the emission spectrum of the Se0 molecule has revealed characteristic new band systems lying in the far and vacuum ultraviolet regions. The results and the analysis of the new systems are presented in this paper. EXPERIMENTAL
PROCEDURE
Using a pure sample of SeOs powder in a conventional discharge tube, the spectrum of Se0 was excited in a 30-Mc,/sec high-frequency discharge from a 168
ULTRAVIOLET
SPECTRUM
OF Se0
169
,iOO-watt oscillator. The discharge is very intense and is deep blue in color. Spectra were photographed from the visible down to vacuum ultraviolet using Hilger large littrow instruments and a one-meter normal incidence vacuum grating spectrograph of 17.3 A/mm. dispersion. Exposures varying from 10 to 30 minut,es duration were found necessary to record the spectra 011 Xgfa Super Special Isopan plates and on Ilford Qz plates. R.ERULTS
AND
ANALYSIS
The results of the present investigation show characteristic discrete band systems in two spectral regions attributable to the diatomic Se0 molecule. The main system of SeO, reported bg earlier workers in the region 0900-U900, is found considerably extended, to consist of new bands up to X5000. The other group of bands lying in the region X2400-X1800 is entirely new. Figure 1 is a reproduction of the spectrum photographed on the vacuum grating sp&rograph. All t,hese bands are degraded toward the violet. Some of them appear with single sharp heads and the others, especially on the short’-wavelength end, occur in pairs. On experimental evidence and on the basis of the vibrat8ional aualysis described below, all the new bands are assigned to the Se0 molecule. Hand heads are measured on the vacuum gratiug spectra with atomic lines as internal standards. 3Ieasurements of individual bands made on different plat,es agree within 3 cm-‘. Table I presents the band head data and the vibrational asaignmentd
of the different
systems.
D-X
3 V’
2
F-X
Fro. 1. The far and vacuum ultraviolet spectrum of Se0 recorded on t,he one-meter 110~ maI incidence vacuum grating spectrograph. The lower state progressions of the different systems are marked.
170
HARANATH TABLE I WAVENUMBERS OF THE Se0 BANDS IN THE REGION X2400 - A1800 AND THEIR VIBRATIONAL ASSIGNMENTS
System F - X (Contd)
System D - X 41078
1, 7
47852
0, 0
41891
1, 6
47940
1, 1
42716
1, 5
48023
2, 2
43553
1, 4
43643
2, 5
47360
0, 4
43736
3, 6
47510
1, 5
44325
0, 2
48235
0, 3
44399
1, 3
48382
1, 4
44480
2, 4
49122
0, 2
44562
3, 5
49259
1, 3
44646
4, 6
49394
2, 4
45184
0, 1
50017
0, 1
45257
1, 2
50264
2, 3
45328
2, 3
51041
1, 1
45398
3, 4
51146
2, 2
46054
0, 0
51940
1, 0
46119
1, 1
52154
3, 2
systemc - x
46119
0, 2
46981
0, 1
47077 47170
51424 51577
0, 3
52325 52480
0, 2
53227 53382
System E - X
SystemF-X
System E - X (Contd)
48905
0, 6
1, 2
49633 49780
0, 5
2, 3
50526 50676
0, 4
54131 54288
'*
The new bands of Se0 have been analyzed as belonging to four different systems designated D-x, F-x, C-X, and E-X starting at the long-wavelength end. System D-x: This system consists of four lower state progressions with v’ = 0, 1, 2, 3. The vibrational constants and the dissociation energy of the lower
ULTRAVIOLET
SPECTRUM
OF Se0
171
state J:are calculated by drawing the AG( U) versus v curve. The following formula represents fairly well the bands assigned to the system: Vu’ .?JM
= 46,023 + 942.0 (v’ +
‘,$) -
3.5 (v’ + j,2;)’
880.0 (0” +
!z)
+ 5.0 (UN+ 1’2):.
(1)
S,@em F-X: This is another brief system with some of its bands overlapping with those of II-x. The analysis indicates that the lower state of this system is the same as that of D-x.
The following approximate vibrational constants
are derived : v,: = 47,807,
me’ = 970,
T,‘w,’ = 6.0, N = 880.0, WP
x,nW<,n= 5.0 cm.
(2)
System C-X: The bands of this system form two characteristic long lower state progressions with U’ = 0 and 1. The Acl-l(u” ) values of these two progressions compare well with those of the ground state of the Se0 molecule. The following vibrational formula is derived from the analysis: lJ*‘$, = 50,862 + 1034.0$
+ ;i’)
-
6.O(v’ + ;i)” 915.0 (UN+ 1.5) + 4.5 (VP + l,.;)?
(:3)
As the lower state is a “Z- state, the upper state C at ve = 50,862 may he a case (b ) state arising from $P I or 3& . System E-X: Bands belonging to this system occur in pairs separated by a wave number interval which varies from 1.57to 147 cm-‘. Six pairs of bands have been observed which appear to constitute a lower state progression with 21’= 0. The A<:(f)
intervals seem to indicate that the lower state is the ground state
of the Se0 molecule. Since the lower state is known to be a “Z state, it is possible that the upper state might arise from a %I term. The mean interval of 1% cm-’ might represent the separation between the ‘II” and 3111components. Thus each band gives rise to two sub-bands arising from 3IIo-aZ- and 31T1-3Z transitions as observed. The sub-band due to 311-3Z- may be too weak to be observed. Since only one ground-state progression of bands is obtained, the constants of the upper level E cannot be determined. DISCUSSION
The four new band systems of Se0 described above appear analogous to some of the systems of S2 in the far and vacuum ultraviolet regions. The vibrational analysis of D-x and F-x systems indicates that the common lower state x has
172
HARANATH
6
5
4 zl I 3
2
I
0
X
FIG. 2. Energy
L level diagram
of the Se0 molecule
a vibrational frequency 880 cm-’ which is close to the value of 915 cm-’ for the ground state X of the Se0 molecule. By analogy with O2 and Sp , this lower state x may be assumed to be a state belonging to the ground-state configuration (za)‘(~=)~(vn)* - kZ+, ‘A, “zl-. As in the case of S2 , the state x may be assumed to dissociate into two normal atoms 3P(Se) + 3P(0) as the ground state X. The position of this level x is then approximately determined as 7780 cm-’ above X from the difference in the dissociation energies of the two states determined by linear extrapolation of their AC?(v) versus u curves. On this basis, the various excited levels of Se0 above the ground state X are shown in Fig. 2. The levels D and F with vibrational frequencies 942 cm-’ and 970 cm-’ may be singlet states of the type Z or II. Each of the states C, D, E, and F with increase in the vibrational frequency relative to the ground state, may correspond to the transition of an electron from the antibonding (UT) orbital to a nonbonding Rydberg orbital.
IyLTRAVIOLET
SPECTRUM
173
OF Se0
ACKNORLEDGMENTS The author wishes to express his grateful thanks to Dr. P. Tiruvenganna Ii. 1~. Rao for their interest in this work.
I&o and Prof.
RECEIVEI~April 16, 1963 REFEREKCES 1. 13 F. HARROW AND E. W. DEI;TSCH, Proc. Phys. Sot. (London) 2. Y. TANAKA AND M. OGAWA, J. Chem. Phys. 36, 726 (1962). 5. P. B. V. HARANATH, 2. Physik. 173,428 (1963).
30,993
(1962).
OF MOLECULAR
SPECTROSCOPY
The Far and
Vacuum
13, 168-173 (1964)
Ultraviolet
Spectrum
of Se0
P. B. V. HARANATH Physics
Department,
Andhra
University, Waltair, India
Four violet degraded band systems C-S, D-x, E-X, and F-x observed in the region X2400-X1800have been newly identified in the emission spectrum of the Se0 molecule excited in an rf discharge. For three of these systems the following vibrational constants in cm-i are derived from the analysis. System C-Iy
D-x F-x
Ye
50,862 46,023 47,807
X,‘W,’
We
1034.o 942.0 970.0
6.0 3.5 6.0
we
I,
915.0 880.0 880.0
x e“co P”
4.5 5.0 5.0
Bands belonging to the E-S system form a single ground-state progression. The lower state z common to D-x and F-x systems is different from the ground state X(W) of the Se0 molecule and is identified as the %+ state arising from the same configuration. Probable electronic transitions responsible for the emission of the four systems have been suggested. INTRODUCTION The emission spectrum of Se0 studied thus far reveals only a number of double headed red degraded bands extending from X3900-X2900. Barrow and Deutsch (1) assigned them to a single system of 3Z--3X- transition similar to the Schumann-Runge band system of oxygen. Recent studies of the emission spectrum of sulfur by Tanaka and Ogawa (2) and by the author (3) have led to the analysis and identification of a number of discrete band systems in the far and vacuum ultraviolet regions. This work has suggested the possibility of the occurrence of similar systems in the spectra of the other homologous molecules of this oxygen group. The present investigation carried out by the author on the emission spectrum of the Se0 molecule has revealed characteristic new band systems lying in the far and vacuum ultraviolet regions. The results and the analysis of the new systems are presented in this paper. EXPERIMENTAL
PROCEDURE
Using a pure sample of SeOs powder in a conventional discharge tube, the spectrum of Se0 was excited in a 30-Mc,/sec high-frequency discharge from a 168
ULTRAVIOLET
SPECTRUM
OF Se0
169
,iOO-watt oscillator. The discharge is very intense and is deep blue in color. Spectra were photographed from the visible down to vacuum ultraviolet using Hilger large littrow instruments and a one-meter normal incidence vacuum grating spectrograph of 17.3 A/mm. dispersion. Exposures varying from 10 to 30 minut,es duration were found necessary to record the spectra 011 Xgfa Super Special Isopan plates and on Ilford Qz plates. R.ERULTS
AND
ANALYSIS
The results of the present investigation show characteristic discrete band systems in two spectral regions attributable to the diatomic Se0 molecule. The main system of SeO, reported bg earlier workers in the region 0900-U900, is found considerably extended, to consist of new bands up to X5000. The other group of bands lying in the region X2400-X1800 is entirely new. Figure 1 is a reproduction of the spectrum photographed on the vacuum grating sp&rograph. All t,hese bands are degraded toward the violet. Some of them appear with single sharp heads and the others, especially on the short’-wavelength end, occur in pairs. On experimental evidence and on the basis of the vibrat8ional aualysis described below, all the new bands are assigned to the Se0 molecule. Hand heads are measured on the vacuum gratiug spectra with atomic lines as internal standards. 3Ieasurements of individual bands made on different plat,es agree within 3 cm-‘. Table I presents the band head data and the vibrational asaignmentd
of the different
systems.
D-X
3 V’
2
F-X
Fro. 1. The far and vacuum ultraviolet spectrum of Se0 recorded on t,he one-meter 110~ maI incidence vacuum grating spectrograph. The lower state progressions of the different systems are marked.
170
HARANATH TABLE I WAVENUMBERS OF THE Se0 BANDS IN THE REGION X2400 - A1800 AND THEIR VIBRATIONAL ASSIGNMENTS
System F - X (Contd)
System D - X 41078
1, 7
47852
0, 0
41891
1, 6
47940
1, 1
42716
1, 5
48023
2, 2
43553
1, 4
43643
2, 5
47360
0, 4
43736
3, 6
47510
1, 5
44325
0, 2
48235
0, 3
44399
1, 3
48382
1, 4
44480
2, 4
49122
0, 2
44562
3, 5
49259
1, 3
44646
4, 6
49394
2, 4
45184
0, 1
50017
0, 1
45257
1, 2
50264
2, 3
45328
2, 3
51041
1, 1
45398
3, 4
51146
2, 2
46054
0, 0
51940
1, 0
46119
1, 1
52154
3, 2
systemc - x
46119
0, 2
46981
0, 1
47077 47170
51424 51577
0, 3
52325 52480
0, 2
53227 53382
System E - X
SystemF-X
System E - X (Contd)
48905
0, 6
1, 2
49633 49780
0, 5
2, 3
50526 50676
0, 4
54131 54288
'*
The new bands of Se0 have been analyzed as belonging to four different systems designated D-x, F-x, C-X, and E-X starting at the long-wavelength end. System D-x: This system consists of four lower state progressions with v’ = 0, 1, 2, 3. The vibrational constants and the dissociation energy of the lower
ULTRAVIOLET
SPECTRUM
OF Se0
171
state J:are calculated by drawing the AG( U) versus v curve. The following formula represents fairly well the bands assigned to the system: Vu’ .?JM
= 46,023 + 942.0 (v’ +
‘,$) -
3.5 (v’ + j,2;)’
880.0 (0” +
!z)
+ 5.0 (UN+ 1’2):.
(1)
S,@em F-X: This is another brief system with some of its bands overlapping with those of II-x. The analysis indicates that the lower state of this system is the same as that of D-x.
The following approximate vibrational constants
are derived : v,: = 47,807,
me’ = 970,
T,‘w,’ = 6.0, N = 880.0, WP
x,nW<,n= 5.0 cm.
(2)
System C-X: The bands of this system form two characteristic long lower state progressions with U’ = 0 and 1. The Acl-l(u” ) values of these two progressions compare well with those of the ground state of the Se0 molecule. The following vibrational formula is derived from the analysis: lJ*‘$, = 50,862 + 1034.0$
+ ;i’)
-
6.O(v’ + ;i)” 915.0 (UN+ 1.5) + 4.5 (VP + l,.;)?
(:3)
As the lower state is a “Z- state, the upper state C at ve = 50,862 may he a case (b ) state arising from $P I or 3& . System E-X: Bands belonging to this system occur in pairs separated by a wave number interval which varies from 1.57to 147 cm-‘. Six pairs of bands have been observed which appear to constitute a lower state progression with 21’= 0. The A<:(f)
intervals seem to indicate that the lower state is the ground state
of the Se0 molecule. Since the lower state is known to be a “Z state, it is possible that the upper state might arise from a %I term. The mean interval of 1% cm-’ might represent the separation between the ‘II” and 3111components. Thus each band gives rise to two sub-bands arising from 3IIo-aZ- and 31T1-3Z transitions as observed. The sub-band due to 311-3Z- may be too weak to be observed. Since only one ground-state progression of bands is obtained, the constants of the upper level E cannot be determined. DISCUSSION
The four new band systems of Se0 described above appear analogous to some of the systems of S2 in the far and vacuum ultraviolet regions. The vibrational analysis of D-x and F-x systems indicates that the common lower state x has
172
HARANATH
6
5
4 zl I 3
2
I
0
X
FIG. 2. Energy
L level diagram
of the Se0 molecule
a vibrational frequency 880 cm-’ which is close to the value of 915 cm-’ for the ground state X of the Se0 molecule. By analogy with O2 and Sp , this lower state x may be assumed to be a state belonging to the ground-state configuration (za)‘(~=)~(vn)* - kZ+, ‘A, “zl-. As in the case of S2 , the state x may be assumed to dissociate into two normal atoms 3P(Se) + 3P(0) as the ground state X. The position of this level x is then approximately determined as 7780 cm-’ above X from the difference in the dissociation energies of the two states determined by linear extrapolation of their AC?(v) versus u curves. On this basis, the various excited levels of Se0 above the ground state X are shown in Fig. 2. The levels D and F with vibrational frequencies 942 cm-’ and 970 cm-’ may be singlet states of the type Z or II. Each of the states C, D, E, and F with increase in the vibrational frequency relative to the ground state, may correspond to the transition of an electron from the antibonding (UT) orbital to a nonbonding Rydberg orbital.
IyLTRAVIOLET
SPECTRUM
173
OF Se0
ACKNORLEDGMENTS The author wishes to express his grateful thanks to Dr. P. Tiruvenganna Ii. 1~. Rao for their interest in this work.
I&o and Prof.
RECEIVEI~April 16, 1963 REFEREKCES 1. 13 F. HARROW AND E. W. DEI;TSCH, Proc. Phys. Sot. (London) 2. Y. TANAKA AND M. OGAWA, J. Chem. Phys. 36, 726 (1962). 5. P. B. V. HARANATH, 2. Physik. 173,428 (1963).
30,993
(1962).