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Infrared spectroscopy of molecular ions in a magnetically confined glow discharge
CI~E~IICAL
INFRARED
SPECTROSCOPY
IN A MAGNETKALLY U. LEMOINE
OF MOLECULAK
CONFINED
and J.L.
PI1YSICS
GLOW
LETI’ERS
2 Novclnbcr 1984
IONS DISCHARGE
DESTOMBl’.S
.-ii rho\vrl by DC I_ucL. tlcrbr~. l’lummcr and I%~kc. ;I is possible lo cnl~~ncc lhc conccnlralion
of ions in a glow dis\Vc h~vc cklcndcd lhc USCof his diwhargc inlo ItIc 10 ~“1 rcyion. Ihpcriwnsiliviry of IIIC rncttIod is ihsrr~~cd by rhc obscrv;llion of IIisnId clcI3ils ~ntlclrschrp cltnr;rclcrislics are given. lk IIC~ Ir2nsJIion5 ol’ 1hc I _ -.- (I+ hnd of 1130’ in z~50 cm Ion!: cell.
CIIX~T by u&g
m~plcl~c
;1 longiIudin31
Ii&i.
I. Introduction Since
McKcllar have recently used this method IO observe the rovihrational spectra of the Hj isotopic forms
IIIC pioneering
Co+ niicrowavc
IqboraIory
1I 1, tlic high-rcsoltJtio11 cohcrcnt
of Jiiolccular
ions using
sources
is a field in rapid cxpnJ1sion. rcgioJ1, dc and rf discliargcs
been IJSCC~ lo product
su~ficienl
ions IO z~llow direct ohscrvlcrion 1r3
and co-workers
It1 Ilic r11illit11cIcr-w3vc hvc
lunahlc
study
of 111c
dcIcctior1
spcclrt~n~ by Woods
COnccJ1IraIi011 of
of their ;Ibsorption
[ 2). III 111~IR rcgioJ1, IIIC first high-rcsoluIioJ1
sorplion
spcctrumofan
ion, tl;,
hy Ok:]. by using frcclucricy IaditiIJo11 1.; J. A111pliIudc hscrvc
oIllsr
111odul~Iion ol’Il1c
h3vc tlcvcloped
niquc in which
Ilic ion drift
velocity
‘I’llis IccliIIiqIJc
is cslrciilcly
pwvcrful.
blc lo di~riiiiiJi31c A nunlbcr
luvc
IIIC molecular
IIIC positive
rhc ncgalivc glow, ir signifjcarrl
colun1u of a dischrgc.
rIicrcr.wavc
spcclrs
ol’scvcrsl
used IO discriminate
field
the ions from
spccics.
111this paper, WC dcscribc into
the cxtcnsion
the IK region.
of this The scnsitiv-
ity achicvcd is illustrated
by the measu’rcmcnt
Ir:tnsiIions
corresponding
IO high rotational
tl1~ 1130+
I - +0°+
and
By working
[9].
of
has beet1 who used
to obscrvc the submilliions
and the
band, recently
observed
of new
levels of by Hacsc
Oka IS].
by
cllllarlcemenl
L’NI hc cxpcc~cd. Tl1is
discharge
neutral
is ~OIIspecific
versus magnetic
lines
2. Experimental
by Dyi11311us rend co-workers.
;I I~ollowca~hodc
this technique
of absorption
by the rc-
1121 and fI,D+
ions xc observed
iJisitls
dcr11onsIrrrIrd
[ 13 ]. Morcovcr,
NO+
spccIrti.
obtairlcd
[04j.
ulsidc
111~ion conccnIrario11
IS].
the 11eg
magnetic
is demonstrated
of new ions:
last type of discharge
:a new tccli-
Ilculral
by this method
observations
the
siiicc il is possi-
been
Iccliniquc
In all 1l1esc works,
cent
another
in which
1111. The dramatic incrcasc in ion concentration
infrrrcd
is modulated
ion spectra from
of rcccnr results
ttus modulation
wmg
field
obtained
ca11 be efficiently
111olccJJh ioJ1s 141. More recently.
and co-workers
by a longitudinal
bchaviour
to
have developed
ativc glow is Icnghtcncd
in 1980
arid co-workers
co-workers
and
spcctromctcr
111odul;1Iior1 of lhc dischrgc
i~sd by Aiii;iiio
c1JrrcnI ~35 firs1 Saykully
wasobtained
S~CCab-
[ IO] _ DC Lucia
1ypc of ri~illimcrcr-wave
Forslcr
3nd
The
&sign.
laser diode spectrometer
It consists mainly
head. Mode selection monochromator matian. a system 0 009-X
14/84/S
(North-~lollantl
modified
03.00 Physics
LS3
is achieved by using a Huct in order
A temperaturecontrolled of fringes
is of conventional
of a Laser Analytics
with
0.0165
to reduce its astig Cc ctalo11, giving
cm-’
spacing. is
0 Elscvicr
Science Publishers
Publishing
Division)
B.V.
VOIUW used
I 1 I, number 3
to interpolate
CIIEMCAL
or cxtrapolatc
the line lo be measured. liquid-nitrogencooled
the wavclcngth
Detection HgCdTc
is achieved
of
by a
detector.
The cdl is a quartz tube 80 cm in length and of The cylindrical cathode and anode are matched to the diameter of the cell and arc made of stainless steel, which gives the most stable discharges. The magnetic field is created by a solenoid which provides a maximum field of 500 G when cooling by liquid nitrogen is used. The length of the solc1 .G cm internal
diameter.
noid is 50 cm and determines
the active
length
of the
and the beginning of the coil is of the order of the cathode dark-space length, typically in the range of a few cm. The discharge current is anlplitude-modulated at 4 kHz. The main effect of the magnetic field is to confine the energetic primary electrons along the axis of 0~ cell. As these electrons very efficiently ionize the molcculcs, Ihe Icngth of the negative glow can be increased up to several times the cell diameter [ I I ] _ This length of course depends on the pressure and 011 the nature of the gas. In our apparatus, a magnetic field of 500 G is needed to obtain a 50 cm long ncgative glow in a Hz discharge a1 a pressure of 100-150 mTorr. From calculations in the framework of a simple 111odcl considering the ions and currents within the calllode dark-space, Maniv et al. 114 ] have derived the following expression relating the current density discharge.
The distance
between
the cathode
end
WYSICS
Z Novcmbcr
LEI-l-ERS
1981
Table 1 Vz~lucs of A and 1’0 corresponding Discharge in Hz at I50 rnTorr - -_____ ~.--..
f3 (G) 0
500 P--P_____
J
,, (,,
,+.-z/3
.-_-_-_--
to the curves
in fis. J.
m4/3) -_
vo (W -__._
60
1550
55
1000
-_
lo the voltage V3 across the discharge:
VJ--
V,=AQ2p,
(1)
whcrc VO is the minimum voltage required to maintain the discharge. Furthermore. they derived a relation giving the A value as a function of physical parameters characterizing the discharge and the nature of the cathode. We have determined the I-V characteristics of a hydrogen discharge with (fig. la) and without (fig. lb) magnetic field. In each case. the solid curve gives the best fit obtained by using eq. (1); the corrcsponding values of V. and A are given in table 1. It appears that a magnetized discharge is niucli easier to star1 than a non-magnetized one. This is well understood, since the magnetic licld reduces the electron loss to the walls. In contrast, the A values are very similar for the magnetized and non-magnetized discharges. This is not unexpected since the cathode dark-space, which mainly governs the characteristics of the discharge [ 151, is outside the magnetic field and therefore is not influenced by its value. A numerical value for A can be derived by using the results given by Maniv et al. (ref. [ 141, eq. (27)). Assuming that the most abundant ion is Hi and taking the experimental value I, = 1 cm for the higth of ltre dark-space, we obtain the value A = 90 V A-‘n m4i3, which is in reasonable agreement with our experimental determination. A similar agreement has been previously found by Maniv et al. in Ar and 0, discharges 1141.
3. Results and discussion
Fig. I. E.\pcrimcntd I- 1’curves: (3) with magnetic field B = 500
G, (b) wirhoui mal;nctic ticId.
mTorr.
Discharge
in HZ Jt 150
The H,O+ ion is produced by a discharge in hydrogen and oxygen @Hz = 150 mTorr,po2 = 10 mTorr) at room temperature. Cooling the discharge always leads to a decrease of the signal. Good results have 285
Volume 1 Ii, number 3
CHEMICAL
PHYSICS
I H30 +
R(5.3)
I$_ 2. Recording of the R(5,3) HJO+ line: (a) with B = 500 G, (b) with B = 0. Lock-in time constant = 300 ms. Len& of the negative dew = 50 cm. I = 1.5mA. Separation between 11112 two OCS lines is 0.03 1.5 cm-‘.
also been obtained in a hydrogen discharge with traces of water. In both cases, a magnetic field of 500 G is needed to obtain the optimum signal. Fig. 2 gives a recording of the R(5,3) line of H,O* with a magnetic field of 500 C and without the magnetic field. The signal enhancement, of the order of 30. emphasizes the role of the magnetic confinement and confirms that the observed line is due to an ion. An unidentified ion line is also clearly detected.
From this recording, we also note that the magnetic field gives rise to a curved
reproduces
baseline
which
actually
the mode of the diode. It indicates
W.1) 2) W-13) N-5 .O) W ,I)
w
Ri5.3) R(6.3)
R(7 .O)
that
1984
the IR beam is amplitude-modulated at the modulation frequency of the discharge current. In view of the typical values obtained in our experiment for the plasma frequency (= 1 GHz), the gyrofrequency (~1.5 CHz) and the collision frequency (l-10 MHz), it appears that this modulation cannot be explained by a direct interaction between the IR beam (Y =Z30000 GHz) and the plasma [ 161. It could bd due to mechanical vibrations of the cell, induced by bombardment of the cathode by energetic ions, a feature already observed in some optogalvanic and optoacoustic experiments in dc discharges [ 171. With the available diode, we have measured some new rotational transitions of the I- + O+ band of H30+. They are given in table 2, second column. The first column gives the wavenumbers predicted by using the molecular constants given by Haese and Oka [8] _We note a disagreement increasing withJ. A preliminary fit including all the measured lines gives the new set of constants reported in table 3. The calculated wavenumbers of the lines observed in this work are given in table 2, third column. The standard deviation of the whole
fit is 0.027 cm-l,
similar to the
value obtained by Haese and Oka [8] for the lower transitions. in conclusion, we point out that a strong enhancement of the H30’ concentration can be obtained by magnetic confinement, even in cells with a small diameter_ Working with larger cells. as in the millimeter-
wave range, will allow the use of an intracell multipass configuration,
which is not possible with the ve-
locity modulation method_ Furthermore. keeping the
Prediclcd a)
Measured
Calculated b)
1051.057 1053.006 1056.334 1066.659 1067.273 1071.329 1087529 1097.073
1050.9x?(5) 1052.920(5) 1056.201(5) 1066.348(5) 1066.978(S) 1072.124(1) 1087.070(10) 1096_391(5)
1050.939
3) Line position predicted \vith constants from ref. [8]. 1)) Cnleulated with the constants given in table 3.
2 November
LETTERS
1052.897 1056.237 1066.405 1067.024 1072.097 1087.113 1096.359
hleasured-calculated 0.012 0.024 0.034 -0.057 -0.046 0.028 -0.043 0.032
Volume f 11. number 3
CffEktfCAL
[I] R.C. Woods. J.
Table 3 ~~ole~~~r
PffYSfCS LETTERS
conslants
~elcrrnin~c~
~-
in the
hlal.
Sfruc~ure
97 (1983)
195,and
r&r-
C”fCS thrrein;
tif
~WI^_“_V.D___~
954.478(14)
1’ 0
11.2635(3O)
B”
Dj
O.~OI5S8(~0) -0.00~~1(~0)
GK C’ - C”
0.13111(SO)
A *
10.6973(27) 0.0004
u; 0; Dji
3) Vduca
a)
7.5 (SO)
-O.O0029(Y2) - oi;-
in pcm~~&ers
-0.001736(50) dcnarn one ztJnr.kkxddcviietion irt
units nf the last quoted di@t.
full iurr specificity of the method seems possible by usirlg a modulation of the negative glow Icng~h by 111carisof 3 transverse magnetic field placed llear the cathode. These ~~b~l~~nI~nt~ art currcrttly in pro
Acknowledgement This work was partidly suppled by the ~‘Centr~ National dc la Recherchc Scientifique” (A.T.P. no. 338-12) and by tic “Etabfissement Public K6gforml
[3] T. Oka, Phys. Rev. Lcrtcrs45 (1980)531. (4 J P. Hcrnath and T. Amano. Phys. Rev. Letters 48 (1982) 30; T. ~1~~. Buff. Sot. Chim. Bet and references ttuzrefn; 1’E 3,39th SyJnT. Am o and J.K.G. Watson, Prmpcr posium on blolccular Spccrroscopy, ColurnbuJ(1984). [S] C.S. eman. M&i. ~~~ern~nn~ J. Pfaff and R.J. kalfy. Phys. Rev. Letters 50 (1983) 727. (S J C.S. Cudeman and R.J. Saykaffy, Ann. Htv. phyr. Chcm. 35 (1984) 387. and references therein. R.S. an. M.W. Crofton and T. Oka, J. Churn. Hays. SO(1 3911. N.N. Mirrsc md T. Oka, J. C2Cm. Phys. 80 (f~~4) 57-7. F.C. van den ffcuvcl. W.L. hleerts and A. Dymsnus. Chcm. Phys. L.crters 80 (1987) 572. S.C. Poster rind A.R.W. kf&cfhr, pJpCr TE 2,39dr Sy~i~~u~l on ~fol~~ul~r Sp~~~~~p~, ~01~~~~5 (1984). P.C. DE Lucia, E. Herbst. CM. Pfummer and C.A. Blake J. C&m. Phys. 78 (1983) 23 12. WC Rowman, E. ffcrbst and F.C. De Lucfa, J. Chem. Phys. 77 (1981) 4262. bf. 1logey.C. Dcmuynck. Ai. Dmh, J.L. Dcrtombcs and FL Lcmoine, Muon. Astrophys. fxrtcrr (1984). to be published; . t4.E. Wtwttrr, W.T. Conner, K,ff. f%trmichl and R.C. Woods, J. Chcm. Pbys. (1984). ~brni1~~~ for pubbcxrrion. S. htsniv. \V.D. Wcstwood and P.J. Sconlon. J. Appl.
~~r~-~~sde~~~~“.
References f I ] T.A. Dixon and R.C. Woods. PJrys. Rev. Letters 34 (f975)6f.
London, 1955). M.A. We&d and C.B. Wharton. Plasma diagnorfics wirh microwwrs (Wff’ilcy,New York. 1965). E. Arimondo. M.C. Divito. 1;. Ernst and hf. fnguscio, I. Phys.. (kris) 44 (1983) C7-367; E. Arfmando. priwte corrluIu~~a~~on (1984).
287
INFRARED
SPECTROSCOPY
IN A MAGNETKALLY U. LEMOINE
OF MOLECULAK
CONFINED
and J.L.
PI1YSICS
GLOW
LETI’ERS
2 Novclnbcr 1984
IONS DISCHARGE
DESTOMBl’.S
.-ii rho\vrl by DC I_ucL. tlcrbr~. l’lummcr and I%~kc. ;I is possible lo cnl~~ncc lhc conccnlralion
of ions in a glow dis\Vc h~vc cklcndcd lhc USCof his diwhargc inlo ItIc 10 ~“1 rcyion. Ihpcriwnsiliviry of IIIC rncttIod is ihsrr~~cd by rhc obscrv;llion of IIisnId clcI3ils ~ntlclrschrp cltnr;rclcrislics are given. lk IIC~ Ir2nsJIion5 ol’ 1hc I _ -.- (I+ hnd of 1130’ in z~50 cm Ion!: cell.
CIIX~T by u&g
m~plcl~c
;1 longiIudin31
Ii&i.
I. Introduction Since
McKcllar have recently used this method IO observe the rovihrational spectra of the Hj isotopic forms
IIIC pioneering
Co+ niicrowavc
IqboraIory
1I 1, tlic high-rcsoltJtio11 cohcrcnt
of Jiiolccular
ions using
sources
is a field in rapid cxpnJ1sion. rcgioJ1, dc and rf discliargcs
been IJSCC~ lo product
su~ficienl
ions IO z~llow direct ohscrvlcrion 1r3
and co-workers
It1 Ilic r11illit11cIcr-w3vc hvc
lunahlc
study
of 111c
dcIcctior1
spcclrt~n~ by Woods
COnccJ1IraIi011 of
of their ;Ibsorption
[ 2). III 111~IR rcgioJ1, IIIC first high-rcsoluIioJ1
sorplion
spcctrumofan
ion, tl;,
hy Ok:]. by using frcclucricy IaditiIJo11 1.; J. A111pliIudc hscrvc
oIllsr
111odul~Iion ol’Il1c
h3vc tlcvcloped
niquc in which
Ilic ion drift
velocity
‘I’llis IccliIIiqIJc
is cslrciilcly
pwvcrful.
blc lo di~riiiiiJi31c A nunlbcr
luvc
IIIC molecular
IIIC positive
rhc ncgalivc glow, ir signifjcarrl
colun1u of a dischrgc.
rIicrcr.wavc
spcclrs
ol’scvcrsl
used IO discriminate
field
the ions from
spccics.
111this paper, WC dcscribc into
the cxtcnsion
the IK region.
of this The scnsitiv-
ity achicvcd is illustrated
by the measu’rcmcnt
Ir:tnsiIions
corresponding
IO high rotational
tl1~ 1130+
I - +0°+
and
By working
[9].
of
has beet1 who used
to obscrvc the submilliions
and the
band, recently
observed
of new
levels of by Hacsc
Oka IS].
by
cllllarlcemenl
L’NI hc cxpcc~cd. Tl1is
discharge
neutral
is ~OIIspecific
versus magnetic
lines
2. Experimental
by Dyi11311us rend co-workers.
;I I~ollowca~hodc
this technique
of absorption
by the rc-
1121 and fI,D+
ions xc observed
iJisitls
dcr11onsIrrrIrd
[ 13 ]. Morcovcr,
NO+
spccIrti.
obtairlcd
[04j.
ulsidc
111~ion conccnIrario11
IS].
the 11eg
magnetic
is demonstrated
of new ions:
last type of discharge
:a new tccli-
Ilculral
by this method
observations
the
siiicc il is possi-
been
Iccliniquc
In all 1l1esc works,
cent
another
in which
1111. The dramatic incrcasc in ion concentration
infrrrcd
is modulated
ion spectra from
of rcccnr results
ttus modulation
wmg
field
obtained
ca11 be efficiently
111olccJJh ioJ1s 141. More recently.
and co-workers
by a longitudinal
bchaviour
to
have developed
ativc glow is Icnghtcncd
in 1980
arid co-workers
co-workers
and
spcctromctcr
111odul;1Iior1 of lhc dischrgc
i~sd by Aiii;iiio
c1JrrcnI ~35 firs1 Saykully
wasobtained
S~CCab-
[ IO] _ DC Lucia
1ypc of ri~illimcrcr-wave
Forslcr
3nd
The
&sign.
laser diode spectrometer
It consists mainly
head. Mode selection monochromator matian. a system 0 009-X
14/84/S
(North-~lollantl
modified
03.00 Physics
LS3
is achieved by using a Huct in order
A temperaturecontrolled of fringes
is of conventional
of a Laser Analytics
with
0.0165
to reduce its astig Cc ctalo11, giving
cm-’
spacing. is
0 Elscvicr
Science Publishers
Publishing
Division)
B.V.
VOIUW used
I 1 I, number 3
to interpolate
CIIEMCAL
or cxtrapolatc
the line lo be measured. liquid-nitrogencooled
the wavclcngth
Detection HgCdTc
is achieved
of
by a
detector.
The cdl is a quartz tube 80 cm in length and of The cylindrical cathode and anode are matched to the diameter of the cell and arc made of stainless steel, which gives the most stable discharges. The magnetic field is created by a solenoid which provides a maximum field of 500 G when cooling by liquid nitrogen is used. The length of the solc1 .G cm internal
diameter.
noid is 50 cm and determines
the active
length
of the
and the beginning of the coil is of the order of the cathode dark-space length, typically in the range of a few cm. The discharge current is anlplitude-modulated at 4 kHz. The main effect of the magnetic field is to confine the energetic primary electrons along the axis of 0~ cell. As these electrons very efficiently ionize the molcculcs, Ihe Icngth of the negative glow can be increased up to several times the cell diameter [ I I ] _ This length of course depends on the pressure and 011 the nature of the gas. In our apparatus, a magnetic field of 500 G is needed to obtain a 50 cm long ncgative glow in a Hz discharge a1 a pressure of 100-150 mTorr. From calculations in the framework of a simple 111odcl considering the ions and currents within the calllode dark-space, Maniv et al. 114 ] have derived the following expression relating the current density discharge.
The distance
between
the cathode
end
WYSICS
Z Novcmbcr
LEI-l-ERS
1981
Table 1 Vz~lucs of A and 1’0 corresponding Discharge in Hz at I50 rnTorr - -_____ ~.--..
f3 (G) 0
500 P--P_____
J
,, (,,
,+.-z/3
.-_-_-_--
to the curves
in fis. J.
m4/3) -_
vo (W -__._
60
1550
55
1000
-_
lo the voltage V3 across the discharge:
VJ--
V,=AQ2p,
(1)
whcrc VO is the minimum voltage required to maintain the discharge. Furthermore. they derived a relation giving the A value as a function of physical parameters characterizing the discharge and the nature of the cathode. We have determined the I-V characteristics of a hydrogen discharge with (fig. la) and without (fig. lb) magnetic field. In each case. the solid curve gives the best fit obtained by using eq. (1); the corrcsponding values of V. and A are given in table 1. It appears that a magnetized discharge is niucli easier to star1 than a non-magnetized one. This is well understood, since the magnetic licld reduces the electron loss to the walls. In contrast, the A values are very similar for the magnetized and non-magnetized discharges. This is not unexpected since the cathode dark-space, which mainly governs the characteristics of the discharge [ 151, is outside the magnetic field and therefore is not influenced by its value. A numerical value for A can be derived by using the results given by Maniv et al. (ref. [ 141, eq. (27)). Assuming that the most abundant ion is Hi and taking the experimental value I, = 1 cm for the higth of ltre dark-space, we obtain the value A = 90 V A-‘n m4i3, which is in reasonable agreement with our experimental determination. A similar agreement has been previously found by Maniv et al. in Ar and 0, discharges 1141.
3. Results and discussion
Fig. I. E.\pcrimcntd I- 1’curves: (3) with magnetic field B = 500
G, (b) wirhoui mal;nctic ticId.
mTorr.
Discharge
in HZ Jt 150
The H,O+ ion is produced by a discharge in hydrogen and oxygen @Hz = 150 mTorr,po2 = 10 mTorr) at room temperature. Cooling the discharge always leads to a decrease of the signal. Good results have 285
Volume 1 Ii, number 3
CHEMICAL
PHYSICS
I H30 +
R(5.3)
I$_ 2. Recording of the R(5,3) HJO+ line: (a) with B = 500 G, (b) with B = 0. Lock-in time constant = 300 ms. Len& of the negative dew = 50 cm. I = 1.5mA. Separation between 11112 two OCS lines is 0.03 1.5 cm-‘.
also been obtained in a hydrogen discharge with traces of water. In both cases, a magnetic field of 500 G is needed to obtain the optimum signal. Fig. 2 gives a recording of the R(5,3) line of H,O* with a magnetic field of 500 C and without the magnetic field. The signal enhancement, of the order of 30. emphasizes the role of the magnetic confinement and confirms that the observed line is due to an ion. An unidentified ion line is also clearly detected.
From this recording, we also note that the magnetic field gives rise to a curved
reproduces
baseline
which
actually
the mode of the diode. It indicates
W.1) 2) W-13) N-5 .O) W ,I)
w
Ri5.3) R(6.3)
R(7 .O)
that
1984
the IR beam is amplitude-modulated at the modulation frequency of the discharge current. In view of the typical values obtained in our experiment for the plasma frequency (= 1 GHz), the gyrofrequency (~1.5 CHz) and the collision frequency (l-10 MHz), it appears that this modulation cannot be explained by a direct interaction between the IR beam (Y =Z30000 GHz) and the plasma [ 161. It could bd due to mechanical vibrations of the cell, induced by bombardment of the cathode by energetic ions, a feature already observed in some optogalvanic and optoacoustic experiments in dc discharges [ 171. With the available diode, we have measured some new rotational transitions of the I- + O+ band of H30+. They are given in table 2, second column. The first column gives the wavenumbers predicted by using the molecular constants given by Haese and Oka [8] _We note a disagreement increasing withJ. A preliminary fit including all the measured lines gives the new set of constants reported in table 3. The calculated wavenumbers of the lines observed in this work are given in table 2, third column. The standard deviation of the whole
fit is 0.027 cm-l,
similar to the
value obtained by Haese and Oka [8] for the lower transitions. in conclusion, we point out that a strong enhancement of the H30’ concentration can be obtained by magnetic confinement, even in cells with a small diameter_ Working with larger cells. as in the millimeter-
wave range, will allow the use of an intracell multipass configuration,
which is not possible with the ve-
locity modulation method_ Furthermore. keeping the
Prediclcd a)
Measured
Calculated b)
1051.057 1053.006 1056.334 1066.659 1067.273 1071.329 1087529 1097.073
1050.9x?(5) 1052.920(5) 1056.201(5) 1066.348(5) 1066.978(S) 1072.124(1) 1087.070(10) 1096_391(5)
1050.939
3) Line position predicted \vith constants from ref. [8]. 1)) Cnleulated with the constants given in table 3.
2 November
LETTERS
1052.897 1056.237 1066.405 1067.024 1072.097 1087.113 1096.359
hleasured-calculated 0.012 0.024 0.034 -0.057 -0.046 0.028 -0.043 0.032
Volume f 11. number 3
CffEktfCAL
[I] R.C. Woods. J.
Table 3 ~~ole~~~r
PffYSfCS LETTERS
conslants
~elcrrnin~c~
~-
in the
hlal.
Sfruc~ure
97 (1983)
195,and
r&r-
C”fCS thrrein;
tif
~WI^_“_V.D___~
954.478(14)
1’ 0
11.2635(3O)
B”
Dj
O.~OI5S8(~0) -0.00~~1(~0)
GK C’ - C”
0.13111(SO)
A *
10.6973(27) 0.0004
u; 0; Dji
3) Vduca
a)
7.5 (SO)
-O.O0029(Y2) - oi;-
in pcm~~&ers
-0.001736(50) dcnarn one ztJnr.kkxddcviietion irt
units nf the last quoted di@t.
full iurr specificity of the method seems possible by usirlg a modulation of the negative glow Icng~h by 111carisof 3 transverse magnetic field placed llear the cathode. These ~~b~l~~nI~nt~ art currcrttly in pro
Acknowledgement This work was partidly suppled by the ~‘Centr~ National dc la Recherchc Scientifique” (A.T.P. no. 338-12) and by tic “Etabfissement Public K6gforml
[3] T. Oka, Phys. Rev. Lcrtcrs45 (1980)531. (4 J P. Hcrnath and T. Amano. Phys. Rev. Letters 48 (1982) 30; T. ~1~~. Buff. Sot. Chim. Bet and references ttuzrefn; 1’E 3,39th SyJnT. Am o and J.K.G. Watson, Prmpcr posium on blolccular Spccrroscopy, ColurnbuJ(1984). [S] C.S. eman. M&i. ~~~ern~nn~ J. Pfaff and R.J. kalfy. Phys. Rev. Letters 50 (1983) 727. (S J C.S. Cudeman and R.J. Saykaffy, Ann. Htv. phyr. Chcm. 35 (1984) 387. and references therein. R.S. an. M.W. Crofton and T. Oka, J. Churn. Hays. SO(1 3911. N.N. Mirrsc md T. Oka, J. C2Cm. Phys. 80 (f~~4) 57-7. F.C. van den ffcuvcl. W.L. hleerts and A. Dymsnus. Chcm. Phys. L.crters 80 (1987) 572. S.C. Poster rind A.R.W. kf&cfhr, pJpCr TE 2,39dr Sy~i~~u~l on ~fol~~ul~r Sp~~~~~p~, ~01~~~~5 (1984). P.C. DE Lucia, E. Herbst. CM. Pfummer and C.A. Blake J. C&m. Phys. 78 (1983) 23 12. WC Rowman, E. ffcrbst and F.C. De Lucfa, J. Chem. Phys. 77 (1981) 4262. bf. 1logey.C. Dcmuynck. Ai. Dmh, J.L. Dcrtombcs and FL Lcmoine, Muon. Astrophys. fxrtcrr (1984). to be published; . t4.E. Wtwttrr, W.T. Conner, K,ff. f%trmichl and R.C. Woods, J. Chcm. Pbys. (1984). ~brni1~~~ for pubbcxrrion. S. htsniv. \V.D. Wcstwood and P.J. Sconlon. J. Appl.
~~r~-~~sde~~~~“.
References f I ] T.A. Dixon and R.C. Woods. PJrys. Rev. Letters 34 (f975)6f.
London, 1955). M.A. We&d and C.B. Wharton. Plasma diagnorfics wirh microwwrs (Wff’ilcy,New York. 1965). E. Arimondo. M.C. Divito. 1;. Ernst and hf. fnguscio, I. Phys.. (kris) 44 (1983) C7-367; E. Arfmando. priwte corrluIu~~a~~on (1984).
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