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An hydroxyl radical infrared laser
Volume 8, number 1
Ch-EMlCAL PHYSICS LETTERS
AN
HYDROXYL
RADICAL
IfiFRARED
LASER
A. B. CALLEAR and H. E. VAN DEN BERGH Lensfield Road, &mt$nOdge, UK
Physical CIze??lisfvLaboratory,
Received 5 October 1970
Mixtures of 03 and H2 were flashed in a laser cavity and stimulated infrared emission was detadted. 2 -1 and 1 -0 fundamentals of the OK raThe radiation was identified as PI transitions of the v=3 -2.
dical.
We wish to report the detection of stimulated emission due to the 2) (vibrational quantum number) = 3 - 2, 2 - 1 and 1 - 0 transitions of the free hydroxyl radical, from mixtures of 03 and H2 flash photolysed in a laser cavity. The observed individual rotational transitions indicate that, during the laser emission, [OH(v=n)] : [OH(v=z-1) J = 0.5. The formation of OH(vs2) in the flash photolysis of 03, H2 and N2 mixtures was detected by Basco and Norrish [l]; photolysis of 03 in the ultraviolet produces O(1D) to generate vibrationally excited OH by the reaction O(lD)+H2’
OHt +H.
(1)
Excited OH radicals are also produced in this system by the reaction
H+o~+oH
t
-+02,
(2)
and Polanyi and co-workers [2] have shown that OH@sS) is formed with total population inversion between all adjacent levels from v=3 - 9 (total pressure IO-4 torr). At higher pressures (lo-2 .torr) the steady state concentrations no longer correspond to population inversion, the most populous level being OH(v=3) - the lowest vibrational state to be observed. The resonator employed in the present research was constructed from a spectrosiI quartz tube (length 2 m and inter@ diameter 22 mm) with gold coated mirrors mounted internally at each end. One Firror was concave with r) radius of 4.71 m, and the dther,was planar. Power was coupled out via‘ a 2 mm diameter hole located at the centre-of the planar’ mirror, -and ,was detect.ed either with a single thermocotipld or wit& a Golay cell. The optical pump-was % spectrosi!. quartz fl+h.lamp power@ wjtb v&qus capa$itars charged 20 20 kV.
The initial experiments were conducted by detection of the undispersed laser emission wi:h a thermocouple. Stimulated emission was found with flash energies in the range 400 - 2000 J, for 03/H2 mixtures at relative partiaL pressures of I : 10, and total pressures of I- 10 torr. Addition
of 70 torr of He did not affect the laser emission; but no stimulated emission could be observed in the presence of ‘70 torr of N2. possibly because of deactivation of O(lD) by the.N2. The total energy of the laser radiation was found to be about one fifth of that of the NOEL photodissociation laser (in the same apparatus) for which Pollack
[3 ] reported a peak power of 10 W. Using a low dispersion monochromator witt wide slits, the frequency of the emitted light was located in the 3050 - 3410 cm-1 range by shiftin the detection region between flashes. With narrow slits, the procedure was then repeated through the established range and seven lines, listed in table I, were found. These experiments were all conducted with t-1 = 1 tom c [HZ] = 9 torr, and 500 J flash energy. The transitions were identified by comparison with the accurate-
Table I
Assignment of the transitions of the 03/H2 laser
Observed -
frequencies
%
Frequencies of the OH radical
(cm-l)
3407 t 2
3407.94 (P1K.L) v = 1 4 0
3368 f 3
3367.01 (PlKg)
1--
3249 t 2
3248.06 (PlKq)
2 --1
3210 f 2
3208.56 (PlK5)
-2 --I
3168 k 2
3167.59 {PlK6)
2 - 1
3092 f 2
3090.09 (PlKq)
3-2
30& f 2 -,
3052.01. (PI KS)
3-2
0
--
..,
.’
_.
:
-. ,. :
-- : 17
Voiume’.S.
.._
numb$r l.
,,.
ly.kno$n fxjec&encies of the infrared transitions Ff 0s [43, In table I the K numbering corresponds to’the iower vibrational s%.te and the F1 compone_nt is the 2n3i2 state. The’particular transitions that werd observed can be rationalised by supposing that [OH(v=n)f/ [O~(tk~t-I)] = 0_5.&~uiqglaser action: In table 2 the corresponc@g relative gains of the various ti&S Of -the ZJ=2 /- t transitioh are iisted. The tabulated gai& 8re relative :
and a 300°K Boltzmann distribution has been assumed. Although total population inversion between vibrationat levels with OH{v>3) is produced in Table2 Xkdive gain-of P transitions with [OH(9=2)}/[OH(u=1)] z if.5 at 300%
Fl
?---- ---K-1-2 q-3 3'4. 445
_ Gain
F2
Gain
-0.179 -0.048 +0.0100 +o ,,.0218
Ic=1-.-2 2-3 3-4 ‘S&-6
54.6
+O.OlGl
5-6
s-r
~+0.007s +0.0030'
6-+7 ?+8
1-s
_-: : _~wluary1971 ‘_
CHEMICALPIZI'PICS~L"JTTERS
.,
-0.137 -0.0505 0.0025 +0.0118 +0.0105 +0.0056 +0.00227
r&a+idn (2j, it is- clear from’ the work-ok Polanyi f21 that the removal of the highey levels,, either by vibrational relaxation or chemical reaction, must be very rapid at the pressurzs employed in the present research. On a particular fundamental, laser emission is probabl!r restricted to a single Py line-for m&t of its &r&ion, but shifts to higher K as the degree of partial inversion decreases .due to vibrational relaxation, For a given K, mrd Boltzmann ciistributioa, the gain is &ways greatest on the F1 component. The new laser may prove to be valuable in probing OH condentrations in chemically reacting systems inctuding the earth’s atmosphere. and coworkers
We thank Dr. D. Tyte of the Services Electronic Research Labor+tories, Baldock, for advice and for the loan of equipment. we are grateful to Professor J. C. Polanyi for communicating resuks prior to publication. We thank the European Space Research Organisation for the award of a Fellowship to H. E. van den Bergh. REFERENCES [l] &Basco at@ R.G. W.Norrish, Proc. Roy. Soc. AZ54 (1960) 317. f2jP. E. Charters, R. G. Macdrmaldand J. C. PoIanyi,. in courseofpublication. [3] M.4. Pollack. Appl. Phys. Letters 3 (l366) 94, [4] G. .“.. Dieke and H. M. Crosswhite, Kaciiatfve Transfer 2 @X2) 97.
J.Quant. Spectry.
_-
-:
.: 1
_ _-
_:-
.
..’
/ .
.
Ch-EMlCAL PHYSICS LETTERS
AN
HYDROXYL
RADICAL
IfiFRARED
LASER
A. B. CALLEAR and H. E. VAN DEN BERGH Lensfield Road, &mt$nOdge, UK
Physical CIze??lisfvLaboratory,
Received 5 October 1970
Mixtures of 03 and H2 were flashed in a laser cavity and stimulated infrared emission was detadted. 2 -1 and 1 -0 fundamentals of the OK raThe radiation was identified as PI transitions of the v=3 -2.
dical.
We wish to report the detection of stimulated emission due to the 2) (vibrational quantum number) = 3 - 2, 2 - 1 and 1 - 0 transitions of the free hydroxyl radical, from mixtures of 03 and H2 flash photolysed in a laser cavity. The observed individual rotational transitions indicate that, during the laser emission, [OH(v=n)] : [OH(v=z-1) J = 0.5. The formation of OH(vs2) in the flash photolysis of 03, H2 and N2 mixtures was detected by Basco and Norrish [l]; photolysis of 03 in the ultraviolet produces O(1D) to generate vibrationally excited OH by the reaction O(lD)+H2’
OHt +H.
(1)
Excited OH radicals are also produced in this system by the reaction
H+o~+oH
t
-+02,
(2)
and Polanyi and co-workers [2] have shown that OH@sS) is formed with total population inversion between all adjacent levels from v=3 - 9 (total pressure IO-4 torr). At higher pressures (lo-2 .torr) the steady state concentrations no longer correspond to population inversion, the most populous level being OH(v=3) - the lowest vibrational state to be observed. The resonator employed in the present research was constructed from a spectrosiI quartz tube (length 2 m and inter@ diameter 22 mm) with gold coated mirrors mounted internally at each end. One Firror was concave with r) radius of 4.71 m, and the dther,was planar. Power was coupled out via‘ a 2 mm diameter hole located at the centre-of the planar’ mirror, -and ,was detect.ed either with a single thermocotipld or wit& a Golay cell. The optical pump-was % spectrosi!. quartz fl+h.lamp power@ wjtb v&qus capa$itars charged 20 20 kV.
The initial experiments were conducted by detection of the undispersed laser emission wi:h a thermocouple. Stimulated emission was found with flash energies in the range 400 - 2000 J, for 03/H2 mixtures at relative partiaL pressures of I : 10, and total pressures of I- 10 torr. Addition
of 70 torr of He did not affect the laser emission; but no stimulated emission could be observed in the presence of ‘70 torr of N2. possibly because of deactivation of O(lD) by the.N2. The total energy of the laser radiation was found to be about one fifth of that of the NOEL photodissociation laser (in the same apparatus) for which Pollack
[3 ] reported a peak power of 10 W. Using a low dispersion monochromator witt wide slits, the frequency of the emitted light was located in the 3050 - 3410 cm-1 range by shiftin the detection region between flashes. With narrow slits, the procedure was then repeated through the established range and seven lines, listed in table I, were found. These experiments were all conducted with t-1 = 1 tom c [HZ] = 9 torr, and 500 J flash energy. The transitions were identified by comparison with the accurate-
Table I
Assignment of the transitions of the 03/H2 laser
Observed -
frequencies
%
Frequencies of the OH radical
(cm-l)
3407 t 2
3407.94 (P1K.L) v = 1 4 0
3368 f 3
3367.01 (PlKg)
1--
3249 t 2
3248.06 (PlKq)
2 --1
3210 f 2
3208.56 (PlK5)
-2 --I
3168 k 2
3167.59 {PlK6)
2 - 1
3092 f 2
3090.09 (PlKq)
3-2
30& f 2 -,
3052.01. (PI KS)
3-2
0
--
..,
.’
_.
:
-. ,. :
-- : 17
Voiume’.S.
.._
numb$r l.
,,.
ly.kno$n fxjec&encies of the infrared transitions Ff 0s [43, In table I the K numbering corresponds to’the iower vibrational s%.te and the F1 compone_nt is the 2n3i2 state. The’particular transitions that werd observed can be rationalised by supposing that [OH(v=n)f/ [O~(tk~t-I)] = 0_5.&~uiqglaser action: In table 2 the corresponc@g relative gains of the various ti&S Of -the ZJ=2 /- t transitioh are iisted. The tabulated gai& 8re relative :
and a 300°K Boltzmann distribution has been assumed. Although total population inversion between vibrationat levels with OH{v>3) is produced in Table2 Xkdive gain-of P transitions with [OH(9=2)}/[OH(u=1)] z if.5 at 300%
Fl
?---- ---K-1-2 q-3 3'4. 445
_ Gain
F2
Gain
-0.179 -0.048 +0.0100 +o ,,.0218
Ic=1-.-2 2-3 3-4 ‘S&-6
54.6
+O.OlGl
5-6
s-r
~+0.007s +0.0030'
6-+7 ?+8
1-s
_-: : _~wluary1971 ‘_
CHEMICALPIZI'PICS~L"JTTERS
.,
-0.137 -0.0505 0.0025 +0.0118 +0.0105 +0.0056 +0.00227
r&a+idn (2j, it is- clear from’ the work-ok Polanyi f21 that the removal of the highey levels,, either by vibrational relaxation or chemical reaction, must be very rapid at the pressurzs employed in the present research. On a particular fundamental, laser emission is probabl!r restricted to a single Py line-for m&t of its &r&ion, but shifts to higher K as the degree of partial inversion decreases .due to vibrational relaxation, For a given K, mrd Boltzmann ciistributioa, the gain is &ways greatest on the F1 component. The new laser may prove to be valuable in probing OH condentrations in chemically reacting systems inctuding the earth’s atmosphere. and coworkers
We thank Dr. D. Tyte of the Services Electronic Research Labor+tories, Baldock, for advice and for the loan of equipment. we are grateful to Professor J. C. Polanyi for communicating resuks prior to publication. We thank the European Space Research Organisation for the award of a Fellowship to H. E. van den Bergh. REFERENCES [l] &Basco at@ R.G. W.Norrish, Proc. Roy. Soc. AZ54 (1960) 317. f2jP. E. Charters, R. G. Macdrmaldand J. C. PoIanyi,. in courseofpublication. [3] M.4. Pollack. Appl. Phys. Letters 3 (l366) 94, [4] G. .“.. Dieke and H. M. Crosswhite, Kaciiatfve Transfer 2 @X2) 97.
J.Quant. Spectry.
_-
-:
.: 1
_ _-
_:-
.
..’
/ .
.