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Far-infrared laser magnetic resonance spectrum of SeD (X2Π32 )
Volume 75, number 1
CHEMICAL
FAR-INFRARED
D I. CLIFF*,
LASER
P.B. DAVIES,
MAGNETIC
PHYSICS
RESONANCE
B J. HANDY,
LCTTERS
SPECTRUM
1 October 1980
OF SeD (X 2H3,t)
B.A THRUSH
Department of Physrcal Chemrstry, fftrn ersrty of Cambridge,, Cambridge CBZ I EP. UK
and E K ?IURRAY
LLOYD
Department of Physics. Casendlsh Laboratory. Utrwerstty of Cambndge. Cambndge. UK Received 3 July 1980
Far-mfrared laser magnetic resonance (LRIR) spectra of ScD have been detected at 5 13 wrn usmg ;1 formic acid laser, and asslgncd to Zeemon components of the J = 3/2 - 5/Z trnnsltlon WIthe SLYisotopic forms c2~so*7e~77~76~7~SeD_ Analyst yields the followmg Bo constants (cm-‘)- “SeD 3 96047. 80ScD 3 96284, 78SeD 3 96532, “SeD 3 96657, ‘%eD 3 96793 and 74SeD 3.97066 These values, combmed with Bo for “SeH from 5 6 pm LRIR, yield re = 0 14634 nm for Sf?D.
1. Introduction
The SeD radical was first observed in the gas phase by Lmdgren [ I] who reported the 2Z-211 absorp-
and analysis of the far-Infrared spectrum arising from the lowest rotational transition m SeD
tlon band In the flash photolysls of D2Se. et al. [2] later obtamed the EPR spectrum
and analysed.
Canington
of SeD m the J = 3/2 level of the *l-I312 state, and values for the rotational constant, A doubling, hyperfine constants and dipole moment. In their work the dlfferent isotopic vanants could not be resolved (except for y7SeD) and the denved rotatIonal constant was an average for the different isotopic species. The rotational transitions of SeD he m the far-infrared re@on and observation of the lowest transition by LMR reported here enables B. to be determined for each isotopic form. Recently, the detectlon and assignment of a farmfrared LMR spectrum of SeH was reported [3]. Transltlons m five isotopic forms were resolved but the frequency of the laser hne used as source was unknown and hence the spectrum was not analysed quantltatlvely. In this paper the detection, assignment * Present address: Department
Sydney, Sydney. NW.
of Chemistry,
Austraha
Umverslty
of
[4],
2.
In which
the spin-orblt
transitlons
are measured
Experimental
The far-infrared optically pumped LMR spectrometer was based on the design of Radford and has been descrrbed in detail [3,5]. SeD radrcals were formed by reacting D atoms, produced by a 2450 MHz discharge through D2 or D,O in Ar, with powdered selenium in an intracavity flow system at total pressures = 0.5 Torr. Magnetic field intensities were measured with a NMR fluxmeter for the centre of each of the narrow doublets observed. These measurements had an estimated uncertamty of I rn 10000 for fields below 1.5 T and 1 m 1000 above 1.5 T. The doublet sphttings were determined by measuring chart records calibrated in terms of magnetic field. Two independent deiermmatrons of the laser frequency are essen9
Volume 75. number 1
CHEUICAL
PHYSICS
LETTERS
1 October
1980
tiafly the same: 584386.9 f 0 7 MHz [6] and 584388.2 MHz [7], they mtroduce a much smaller uncertamty into the results than do the field measurements_
3. Results and analysis Spectra due to the six naturally occurnng Isotopes of selenium, which vary in abundance from 0.87 to 49 8% were detected. The occurrence of paus of lines with separation < 1 mT due to A doublmg can clearly be seen m-fig 1. Hyperfine structure due to 77Se (I = l/2) was also resolved but not the deutenum hyperfine splitting. The measured fields for the centres of the A doublets and theu sphttmgs are m table 1. The latter showed no detectable variatron between the isotopic specres and only a mean value IS grven. The 5 13 pm laser lme of fomnc acrd hes w~thm the tuning range of the J = 312 --f S/2 transrtron m SeD. The zero-field spacmg for the trnnsrtion in 80SeD was calculated by assignmg the values -1764.4 cm-1 toAo [8] ,3.940cm-t toBo [2] and 8.7 X 1O-5 cm-t to Do_ The latter was calculated from the formula 48,3/o~z [4] and is consrstent with the value of Do for SeH [8] and the usual relation for isotopes. A simple calculatron based on a lmear Zeeman effect shows that the transitions iWJ = 312 - 3J2, S/2 + l/2, 112 4 -l/2 and 312 + S/2 should appear at around
40
SLO
10
bO0
580
b20mT
Ibl
*-i-t-h950
1wo
Iis0rnT
no0
x)50
ICI
p
750,s 10, 1020 and 1500 niT respectively. Scahng the zero-field interval accordmg to mass and usmg the known abundance rattos, permtts the complete assignment given m table 1. Spectra due to the heavier Se isotopes appear at lower magnetrc fields because the laser frequency IS less than the zero-field Frequency of the transrtion. Accurate values for the rotatronal constant B, for each isotopic form were obtamed by fitting the LMR data in the least-squares routine The program utrlised the harmltonian and matrix elements developed for OH [9] and prevrously used for anafysmg LMR spectra of SH [lo] . Because the A doubling IS small, the average field posrtions for each pair of LMR doublets were used u-r the fit. A0 was fixed at Its value given m the followmg paper although the fit is msensitrve to the value of A0 and is essentially unchanged If the earher value [8]
SbO
9;10
mT
Fig 1 f=3/2-f=
Laser magnetrc resonance spectrum of SeD (XZn3,2) 512 (a) Mj = 312 - fifj = l/2, (b) I%$’ = i/2 -+ nf> = -l/2, Cc)hIj’ = iW>= 3/2 In all cases the most rntense trnnsrtron corresponds to the most abundant rsotoprc specres *OSeD and transltlons
magnehc
for hghter Isotopes appear at higher
field
1s used. Do was also kept constant, at 8.7 X 1O-5 cm-l, as only one rotational transrtron was observed. The value of the spin-rotation parameter determined from the electronic spectrum of SeD was used [ 111. The formulation of the 211 Zeeman hamrltonian used mcorporates s~xg-factors ]9]. However, far more data than available here would be requrred to determine these for SeD. Instead gs was taken from the
Volume 75, number
1
CHEMICAL
PHYSICS
LETTERS
Table 1 Field posItIons a) (mT) of the 5 13 pm Lhl R hnes of SeD (X Zn31z) J = 3/2 -
~
My - “fj
312 -
312
82SeD 80SeD 78SeD “SeD
804.93 842 57 882 00 887 93 915 23 923 61 966 80
1 October 1980
5/2
312 -L l/2
112 + -112
312 -
512
531 96 556 68 582 63 581 24 610 02 609.79
975 72 1022 12 1070.93 1082.34 1110 1.5 112’61 1176 91
1636.6 1712 7 1792 5 1819 9 1849 0 1875 6
~-~
‘%eD 74S~D
---
a) PosItIon of the centre of the doublets Althoueh field posItIon was used m the fit and transltlons
--
-~
paus of hncs arlsmg from A doubhns were rcsoivcd (fig. I) only the centrc above 1 5 T were elven a \vclghtm, 0 one-tenth those of the lower field transt-
t1ons. work of Brown et al. [12] on SeH and values for& and g, for each Isotope were obtamed from the leastsquares routine, although these were found to be determmed with IlttIe statIstIcal slgnlficance The values of Bo obtamed for the SIX isotopic forms of SeD dre m table 2. These are given in terms of an R2 hamdtoman [9] and are therefore m less than would be obtamed by an expansion In terms of N’, as IS used m the accompanymg paper [4]. The observed A doubhngs for the 3/2 + 312, 312 + l/2, l/2 + -l/2 and 312 + S/2 were 5.78 +O 05, 5.70 -+ 0 OS,6 22 -+ 0.1 and 5 42 -C0 05 MHz respectively. The mean value of 5.78 f 0.33 MHz Bves q,, = 321 f 18 kHz. Thus corresponds to a A doubhng of 1.93
* 0.11 MHz for the J = 3/2 level, III agreement
with the values of 1.90 MHz measured by Carrington et aI_ 121. The measured 77Se hyperfine splrttrng also agreed well with the value from the EPR spectrum 12) _
4. Discussion RotatIonal constants derived from EPR spectra of ‘fl radicals are calculated from the second-order Zeeman effect whxh 1s responsible for the resolution of different MJ components. Ths IS a less direct method than LMR, so the improved accuracy of the latter measurement (table 2) IS not surpnsmg. To test the rC was
required Table 2 Rotat1on.d
values reported
in table 1,
calculated for each isotopic form. $eD values in the calculation were estimated reIationshlps [ 131 -
using sim-
ple tsotope constants
Bg of lsotoplc
LhlR a) (thrs work) __ 8zSeD 8oSeD *SeD “SeD 76SeD 74SeD
of the set of B,
consistency
3 96047(4) 3.96284(4) 3 96532(4) 3 96657(4) 3 96793(4) 3 97066(4)
forms of SeD (X ‘n3,2) EPR b) I?-]
3.940(5)
a) FIxed parameters were& = -1762.789 cm-l, Do = 8 7 x lo-’ cm-‘, 7 = -0 50 cm- t [11~,gs=2.00122 [12],gi = 1.00072,gr = -4 9 X lo4 [4]. Uncertamtles m the LblR results are three standard deviations of the Ieastsquares tit for which the rms error was less than 400 kHz. The uncertatnty in -y mtroduces an addItiona error of ,-2 6 x lo4 cm-‘. b) Isotopic forms not resolved.
BScD _ ,+,Seff 0
= ;#‘&
_ I),
where P
2 = $eH/$eD.
[ 121 for g”SeH and Assummg Bo = 7.78734 cm-t our value of B. for gOSeD, cy, for 8oSeD detennmed in thus way IS 0.0875 cm-* whxh IS in good agreement ~th unpublished results of Brown and Fackerell on the \nbratlon-rotation spectrum. aFD was calculated for each isotopic form to derive re. The values obtained for all the selemum isotopes agreed to within 1 part in 105 and yielded re = O.146345 nm. The consistency of this result is highly satisfactory within the lunltations of the sunple theory used and establishes the precisron of the measurement. The absolute ac-
Volume
75, number
CHEMICAL
1
curacy of our values of B, and hence of re depend on parameters from other spectroscoprc studies, notably y and D The largest contrrbution comes from the spin-rotation parameter y, which contributes an uncertamty of 5 X 1O-6 nm to the bond length grven above.
Acknowledgement
We thank the SRC and the Royal Socrety for equipment grants and the SRC for support for BJH and EKML. We are grateful to Dr D.K. Russell for use of his computer program and to Dr J.M. Brown for commumcating the results of his CO LMR expenments prror to pubhcatron.
References [I]
12
B Lmdgren,
J hlol
Spectry
28 (1968)
536
PHYSICS
LETTERS
1 October
1980
[2] A. Carrmgton, G N Currle and N J D. Lucas, Proc Roy Sot. A315 (1970) 355 [3] P B. Davies, B.J Handy, E K hlurray Lloyd and D K Russell, J. Chem Phys 68 (1978) 3377. [4] J hl Brown, A Carrmgton and A.D Fackereli, Chem Phys Letters 75 (1980) 13. [5] I- D Wayne and H E. Radford, Mol. Phys 32 (1976) 1407 [6] H.E Radford, F R Peterson, D A. Jcnnmgs and J A hlucha, IEEE J Quantum Electron. 13 (1977) 92 [7] A. Dcldalte, D Dangolsse, J P Splmgard and J Bcllet, Opt Commun 22 (1977) 333 [S] P Bollmark, B Lmdgren, B. Rydh and U. Sasscnberg. Physxa Scrlpta 17 (1978) 561 [9] J hl Brown hl. Ka~se, C h1.L Kerr and D_J hldton, hlol Phys 36 (1978) 553. [lo] P B Dawes, B J Handy, E K hlurray Lloyd and D K. Russell, hlol Phys 36 (1978) 1005. [I 11 P Bollmark, B. Lmdgrcn and U Sassenberg, Physlca ScrIpta 21 (1980) 811 [ 121 J hl Broitn, A Carrmgton and T J. Sears, hlol Phys 37 (1979) 1837 [ 131 C. Herzbeg, Spectra of dlatomlc molecules, 2nd Ed (Van Nostrand, Prmccton, 1950)
CHEMICAL
FAR-INFRARED
D I. CLIFF*,
LASER
P.B. DAVIES,
MAGNETIC
PHYSICS
RESONANCE
B J. HANDY,
LCTTERS
SPECTRUM
1 October 1980
OF SeD (X 2H3,t)
B.A THRUSH
Department of Physrcal Chemrstry, fftrn ersrty of Cambridge,, Cambridge CBZ I EP. UK
and E K ?IURRAY
LLOYD
Department of Physics. Casendlsh Laboratory. Utrwerstty of Cambndge. Cambndge. UK Received 3 July 1980
Far-mfrared laser magnetic resonance (LRIR) spectra of ScD have been detected at 5 13 wrn usmg ;1 formic acid laser, and asslgncd to Zeemon components of the J = 3/2 - 5/Z trnnsltlon WIthe SLYisotopic forms c2~so*7e~77~76~7~SeD_ Analyst yields the followmg Bo constants (cm-‘)- “SeD 3 96047. 80ScD 3 96284, 78SeD 3 96532, “SeD 3 96657, ‘%eD 3 96793 and 74SeD 3.97066 These values, combmed with Bo for “SeH from 5 6 pm LRIR, yield re = 0 14634 nm for Sf?D.
1. Introduction
The SeD radical was first observed in the gas phase by Lmdgren [ I] who reported the 2Z-211 absorp-
and analysis of the far-Infrared spectrum arising from the lowest rotational transition m SeD
tlon band In the flash photolysls of D2Se. et al. [2] later obtamed the EPR spectrum
and analysed.
Canington
of SeD m the J = 3/2 level of the *l-I312 state, and values for the rotational constant, A doubling, hyperfine constants and dipole moment. In their work the dlfferent isotopic vanants could not be resolved (except for y7SeD) and the denved rotatIonal constant was an average for the different isotopic species. The rotational transitions of SeD he m the far-infrared re@on and observation of the lowest transition by LMR reported here enables B. to be determined for each isotopic form. Recently, the detectlon and assignment of a farmfrared LMR spectrum of SeH was reported [3]. Transltlons m five isotopic forms were resolved but the frequency of the laser hne used as source was unknown and hence the spectrum was not analysed quantltatlvely. In this paper the detection, assignment * Present address: Department
Sydney, Sydney. NW.
of Chemistry,
Austraha
Umverslty
of
[4],
2.
In which
the spin-orblt
transitlons
are measured
Experimental
The far-infrared optically pumped LMR spectrometer was based on the design of Radford and has been descrrbed in detail [3,5]. SeD radrcals were formed by reacting D atoms, produced by a 2450 MHz discharge through D2 or D,O in Ar, with powdered selenium in an intracavity flow system at total pressures = 0.5 Torr. Magnetic field intensities were measured with a NMR fluxmeter for the centre of each of the narrow doublets observed. These measurements had an estimated uncertamty of I rn 10000 for fields below 1.5 T and 1 m 1000 above 1.5 T. The doublet sphttings were determined by measuring chart records calibrated in terms of magnetic field. Two independent deiermmatrons of the laser frequency are essen9
Volume 75. number 1
CHEUICAL
PHYSICS
LETTERS
1 October
1980
tiafly the same: 584386.9 f 0 7 MHz [6] and 584388.2 MHz [7], they mtroduce a much smaller uncertamty into the results than do the field measurements_
3. Results and analysis Spectra due to the six naturally occurnng Isotopes of selenium, which vary in abundance from 0.87 to 49 8% were detected. The occurrence of paus of lines with separation < 1 mT due to A doublmg can clearly be seen m-fig 1. Hyperfine structure due to 77Se (I = l/2) was also resolved but not the deutenum hyperfine splitting. The measured fields for the centres of the A doublets and theu sphttmgs are m table 1. The latter showed no detectable variatron between the isotopic specres and only a mean value IS grven. The 5 13 pm laser lme of fomnc acrd hes w~thm the tuning range of the J = 312 --f S/2 transrtron m SeD. The zero-field spacmg for the trnnsrtion in 80SeD was calculated by assignmg the values -1764.4 cm-1 toAo [8] ,3.940cm-t toBo [2] and 8.7 X 1O-5 cm-t to Do_ The latter was calculated from the formula 48,3/o~z [4] and is consrstent with the value of Do for SeH [8] and the usual relation for isotopes. A simple calculatron based on a lmear Zeeman effect shows that the transitions iWJ = 312 - 3J2, S/2 + l/2, 112 4 -l/2 and 312 + S/2 should appear at around
40
SLO
10
bO0
580
b20mT
Ibl
*-i-t-h950
1wo
Iis0rnT
no0
x)50
ICI
p
750,s 10, 1020 and 1500 niT respectively. Scahng the zero-field interval accordmg to mass and usmg the known abundance rattos, permtts the complete assignment given m table 1. Spectra due to the heavier Se isotopes appear at lower magnetrc fields because the laser frequency IS less than the zero-field Frequency of the transrtion. Accurate values for the rotatronal constant B, for each isotopic form were obtamed by fitting the LMR data in the least-squares routine The program utrlised the harmltonian and matrix elements developed for OH [9] and prevrously used for anafysmg LMR spectra of SH [lo] . Because the A doubling IS small, the average field posrtions for each pair of LMR doublets were used u-r the fit. A0 was fixed at Its value given m the followmg paper although the fit is msensitrve to the value of A0 and is essentially unchanged If the earher value [8]
SbO
9;10
mT
Fig 1 f=3/2-f=
Laser magnetrc resonance spectrum of SeD (XZn3,2) 512 (a) Mj = 312 - fifj = l/2, (b) I%$’ = i/2 -+ nf> = -l/2, Cc)hIj’ = iW>= 3/2 In all cases the most rntense trnnsrtron corresponds to the most abundant rsotoprc specres *OSeD and transltlons
magnehc
for hghter Isotopes appear at higher
field
1s used. Do was also kept constant, at 8.7 X 1O-5 cm-l, as only one rotational transrtron was observed. The value of the spin-rotation parameter determined from the electronic spectrum of SeD was used [ 111. The formulation of the 211 Zeeman hamrltonian used mcorporates s~xg-factors ]9]. However, far more data than available here would be requrred to determine these for SeD. Instead gs was taken from the
Volume 75, number
1
CHEMICAL
PHYSICS
LETTERS
Table 1 Field posItIons a) (mT) of the 5 13 pm Lhl R hnes of SeD (X Zn31z) J = 3/2 -
~
My - “fj
312 -
312
82SeD 80SeD 78SeD “SeD
804.93 842 57 882 00 887 93 915 23 923 61 966 80
1 October 1980
5/2
312 -L l/2
112 + -112
312 -
512
531 96 556 68 582 63 581 24 610 02 609.79
975 72 1022 12 1070.93 1082.34 1110 1.5 112’61 1176 91
1636.6 1712 7 1792 5 1819 9 1849 0 1875 6
~-~
‘%eD 74S~D
---
a) PosItIon of the centre of the doublets Althoueh field posItIon was used m the fit and transltlons
--
-~
paus of hncs arlsmg from A doubhns were rcsoivcd (fig. I) only the centrc above 1 5 T were elven a \vclghtm, 0 one-tenth those of the lower field transt-
t1ons. work of Brown et al. [12] on SeH and values for& and g, for each Isotope were obtamed from the leastsquares routine, although these were found to be determmed with IlttIe statIstIcal slgnlficance The values of Bo obtamed for the SIX isotopic forms of SeD dre m table 2. These are given in terms of an R2 hamdtoman [9] and are therefore m less than would be obtamed by an expansion In terms of N’, as IS used m the accompanymg paper [4]. The observed A doubhngs for the 3/2 + 312, 312 + l/2, l/2 + -l/2 and 312 + S/2 were 5.78 +O 05, 5.70 -+ 0 OS,6 22 -+ 0.1 and 5 42 -C0 05 MHz respectively. The mean value of 5.78 f 0.33 MHz Bves q,, = 321 f 18 kHz. Thus corresponds to a A doubhng of 1.93
* 0.11 MHz for the J = 3/2 level, III agreement
with the values of 1.90 MHz measured by Carrington et aI_ 121. The measured 77Se hyperfine splrttrng also agreed well with the value from the EPR spectrum 12) _
4. Discussion RotatIonal constants derived from EPR spectra of ‘fl radicals are calculated from the second-order Zeeman effect whxh 1s responsible for the resolution of different MJ components. Ths IS a less direct method than LMR, so the improved accuracy of the latter measurement (table 2) IS not surpnsmg. To test the rC was
required Table 2 Rotat1on.d
values reported
in table 1,
calculated for each isotopic form. $eD values in the calculation were estimated reIationshlps [ 131 -
using sim-
ple tsotope constants
Bg of lsotoplc
LhlR a) (thrs work) __ 8zSeD 8oSeD *SeD “SeD 76SeD 74SeD
of the set of B,
consistency
3 96047(4) 3.96284(4) 3 96532(4) 3 96657(4) 3 96793(4) 3 97066(4)
forms of SeD (X ‘n3,2) EPR b) I?-]
3.940(5)
a) FIxed parameters were& = -1762.789 cm-l, Do = 8 7 x lo-’ cm-‘, 7 = -0 50 cm- t [11~,gs=2.00122 [12],gi = 1.00072,gr = -4 9 X lo4 [4]. Uncertamtles m the LblR results are three standard deviations of the Ieastsquares tit for which the rms error was less than 400 kHz. The uncertatnty in -y mtroduces an addItiona error of ,-2 6 x lo4 cm-‘. b) Isotopic forms not resolved.
BScD _ ,+,Seff 0
= ;#‘&
_ I),
where P
2 = $eH/$eD.
[ 121 for g”SeH and Assummg Bo = 7.78734 cm-t our value of B. for gOSeD, cy, for 8oSeD detennmed in thus way IS 0.0875 cm-* whxh IS in good agreement ~th unpublished results of Brown and Fackerell on the \nbratlon-rotation spectrum. aFD was calculated for each isotopic form to derive re. The values obtained for all the selemum isotopes agreed to within 1 part in 105 and yielded re = O.146345 nm. The consistency of this result is highly satisfactory within the lunltations of the sunple theory used and establishes the precisron of the measurement. The absolute ac-
Volume
75, number
CHEMICAL
1
curacy of our values of B, and hence of re depend on parameters from other spectroscoprc studies, notably y and D The largest contrrbution comes from the spin-rotation parameter y, which contributes an uncertamty of 5 X 1O-6 nm to the bond length grven above.
Acknowledgement
We thank the SRC and the Royal Socrety for equipment grants and the SRC for support for BJH and EKML. We are grateful to Dr D.K. Russell for use of his computer program and to Dr J.M. Brown for commumcating the results of his CO LMR expenments prror to pubhcatron.
References [I]
12
B Lmdgren,
J hlol
Spectry
28 (1968)
536
PHYSICS
LETTERS
1 October
1980
[2] A. Carrmgton, G N Currle and N J D. Lucas, Proc Roy Sot. A315 (1970) 355 [3] P B. Davies, B.J Handy, E K hlurray Lloyd and D K Russell, J. Chem Phys 68 (1978) 3377. [4] J hl Brown, A Carrmgton and A.D Fackereli, Chem Phys Letters 75 (1980) 13. [5] I- D Wayne and H E. Radford, Mol. Phys 32 (1976) 1407 [6] H.E Radford, F R Peterson, D A. Jcnnmgs and J A hlucha, IEEE J Quantum Electron. 13 (1977) 92 [7] A. Dcldalte, D Dangolsse, J P Splmgard and J Bcllet, Opt Commun 22 (1977) 333 [S] P Bollmark, B Lmdgren, B. Rydh and U. Sasscnberg. Physxa Scrlpta 17 (1978) 561 [9] J hl Brown hl. Ka~se, C h1.L Kerr and D_J hldton, hlol Phys 36 (1978) 553. [lo] P B Dawes, B J Handy, E K hlurray Lloyd and D K. Russell, hlol Phys 36 (1978) 1005. [I 11 P Bollmark, B. Lmdgrcn and U Sassenberg, Physlca ScrIpta 21 (1980) 811 [ 121 J hl Broitn, A Carrmgton and T J. Sears, hlol Phys 37 (1979) 1837 [ 131 C. Herzbeg, Spectra of dlatomlc molecules, 2nd Ed (Van Nostrand, Prmccton, 1950)