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Thermally initiated HF chemical laser
Volume 8.. number 2
CHEMICAL PHYSICS LETTERS
.
_
THERMALLY
Los Alamos
INITIATED
RF
CHEMICAL
15 January 1971
LASER
R. J. JENSEN and W. W. RICE * Scientific Lubomtory of the Unfversity of Califvku, Los Alamos,
New Mexico,. USA
Received 30 November 1970 The ClN explosion has been used to thermally decompose NF3 and SF into fluorine atoms which react with 4 2 producing HF laser action. The reaction of i3 ato:n on fluor Bne bearing species is indicated by 4-3IiF laser transitions.
HF laser action has been observed from the reaction of thermally decomposed gaseous fluorides with hydrogen. This thermal triggering of the laser producing chemical reaction is capable of quantitatively decomposing many gaseous fluorides as hdmogeneously as a flash lamp but with a much smaller electrical energy requirement. Fumermore, thermal triggering is not limited to prossure regimes in which an electric discharge can be pbtained. In this work a xenon flash lamp was used to trigger the explosion of ClN3 which was present in tertiary mixtures ClN3 +-NF3 + H2 and ClN3 + SF6 t H2. The compounds NF6 and SF6 are known to have very little optical absorption [1,2] in the spectral region of xenon flash lamps, and, indeed, the binary mixtures NF3 + H2 and SF6 + 22 could not be made to react by flash lamp initiation in this series of experiments. However, with 12-25 mole percent ClN3 added to these mixtures a sharp laser pulse was emitted. Pulsed RF laser oscillation from NFQ + H2 mixtures has prwioudy been reported by Gregg et al. [3]. The reaction in these mixtures was initiated by an electron beam, Electric discharge initiation of SF6 t Hi mixtures has been reported by Jensen and Rice [4]. Spencer et aL [5] have thermally decomposed SF6 to provide F atoms which when mixed with H2 produced laser oscillation in a flowing system. The present letter describes chemical laser action resulting from the thermal production of F atoms in premixed laser gases.
For this experiment a quartz laser tube 124
cm long and 21 mm in d&meter was fitted with scum chloride windows at the Brewster angle. The laser tube was positioned midway between * Supportedby Atomic ‘Energy Commision ‘andAsee ciated,Western Uqiversities graduate fellowship.
214 :
.
two totally reflecting,
gold surfaced mirrors of 10 m radius of curvature which were 202cm apart. A portion of the laser flux was reflected out of the cavity by slightly misaligned Brewster angle windows affording two convenient beams for monitoring the laser oscillation. The radiation reflected from one window was focused by a spherical mirror on a Philco GPC-215 Au:Ge detector., The reflection from the other window was focused on the entrance slits of a 0.5 m Jarrell Ash monochromator which was fitted with a Bausch and Lomb grating blazed at 9p. The HF rotation-vibration transitions were observed in third order using a Philco GPC-216 detector positioned at the exit slits of the monochromator. A Tektronix 555 dual beam oscilloscope followed the response from both detectors simultaneously. The oscilloscope was triggered by an RCA 929 vacuum photodiode monitoring the output of a 76 cm xenon flash lamp which was positioned against the laser tube to initiate
the CIN3 explosion.
The ClN3 was generated by the method of Raschig [6] (acidifying an aqueous solution containing equimolar concentrations of NaOCL and NaN$. The gases used were Air Products 9’7.5% minimum purity NF3, Allied Chemical 96% minimum purity SF6, and Linde- 99.99%minimum purity Ho. The chemicals used in the synthesis of GIN3 included MC&B practical grade NaN3, B.&I u.s.p. grade H3BO3, and B&A reagent grade NaCQ 5% solution. HaIocarhon 25-55 grease was used on all ground glass joints and stopcocks throughout the system. The ClN3 + NF3.+ H2 mi&ures were fired at
several molar ratios: 1 ClN311 NF3/6 H2, 1 ClN3/2 NF3/5 Hz, -2 ClN3/2 NF3/4 H2 and
3 CW~/l NF3/4 Hr The most successful results were obtained from the Jj1/2- ratio at pressures .betw&n 12 and 24 to+. The‘ laser..t&hsitions . ._
t Volume 3, number
2
CHEMICAL PHYSICS LETTERS orated
Tabie 1 HF laser lines observed in 3 2ClN3/2NF3/4H2 ratio mixture l-+0
2-l
3d2
4-3
p3 (5)
P4(5) P4@)
Pl@)
p2 (6)
p3 (6)
PlOO)
P2 (7)
p3 (7)
P2 (8)
p3 (8)
Pl (11)
molar
p2 (9)
P,(8)
TOTAL INITIAL
PRESSURE 16.3
TORR
P,(7)
from
the action
of F atoms
and XF,
only a
qualitative comparison of relative intensities carr be made. The pulse width on the upper trace is broader than the lower trace because a 1000 ohm resistor instead of a 51 ohm resistor was used to determine @e oscilloscope input. The full width of the HF pulse was between 0.5 and I lrsec and the peak power was two orders of magnitude greater than that of the HCL’lasers previously fired in the same optical cavity. A ClN3 + SF8 + H2 mixture at 24 mole percent ClN3, 19 mole percent SF6, and 57 mole percent H2 was also fired successfully. A major probLem with the SF6 system was that the reaction deposited an abundance of sulphur throughout the laser tube which necessitated swabbing the tube out between shots. The laser oscillation for this mixture exhibited the same type narrow, intense laser spike. The CINQ absorption spectrum [7] in the nearultraviolet overlaps the emission spectrum of the xenon flash lamp, so that the highly exothermic reaction
ClN3 + 12v-+C12 + 4 N2, AH = - 93.2 kcal “mole
TOTAL INITIAL
PRESSURE 15,8
TORR
P4(6)
is initiated, producing temperatures of several thousand degrees [8]. During the explosion of the tertiary mixtures, the NF3 or SF8 is substantially dissociated into F atoms allowing the reaction F + H2-+HF + H,
AH = -31.8 kcal/mole
TOTAL INITIAL
PRESSURE 13.1
TORR
(EA = 1.7 kcaljmole) FLASH LAEP
to populate the Oth, lst, 2nd and 3rd vibrational levels of HF (see table 2). It is interesting to Table 2
FLASH LAMP
Fig. 1. Laser emission fro? 2ClN3/2NF3/4H2 molar r.atio mixture. Time scale 1 psec/div., arbitrary intensity scale.
observed under these conditions are Listed in table 1. In fig. 1 an intense rotational-vibrational line. for several of the observed vIbrational transitions is shown along with.+te total laser-pulse. -Since the NaCl Brewster _windoFs rapidly deteri’
Energy needed for population of vibrationz&ly &cited states
Vibrational transition
Band origin in cm -1
Band origin
in kcnt/moIe
041
3961.6
11.3
o-2
7751.0
22.2
o-+3
11373.0
32.5
0 4.4
148i1.9
-
42.4
Volume 8,jumber .
2
‘_ 1
P (6) trax&ions seved. Bc”aus6 the %I2.4 kcal/mo!e’ populate the 4th jibratioti1 level of avai&ble in the-pr,&ceding.reaction; P4(6) transition& mu&be attributed note that P#).and
energetic reaction
-CHEMICALPHYsICS’iET’rERS
~.
were-&b:
:
required to HF are not the P&5) and -’ to tlie more :
R+N-F~((x~~)~HF+NF~_~, : AH =. -70 kcal/mole. From the authors’ prewious experience [g] with ClN3 in H3 containing systems HCXlaser lines would have been expected.. A scan of the lines Pz(6); 32(‘7) tid P2(8) of HCl showed that they were not present in this expegment.
REFERENCES
.. _ ..
:.
=.
.[I;.% FL LaPaglia and h.B. F. Duncan, _J,Cheti. Phys.
34 (1961) 1003. -[2]T.itl. &MoeandA.B.F.Duacaa. J.Chem.Phys. 19 (lxil) 71. 131 D.W. Gregg, B.Krawetz. R.K.Pears&, B.R. Schleicher, S.J.Thomas, E.B.Huss. K.J.Pettipiece, -J. R. Creighton.. Et.E. Niver and Y. L. Pan, UCRL Preprint-72434 (1970). [4] R. J..Jeensenand W. W. Rice, Chem. Phys. Letters 7 (1970) 627. [5] D. J.Spencer. H. Mirels. T. A. Jacobs and R.W. F. Gross, Appl. Phys. Letters 16 (1970) 235. [S] F. Raschig, Chem. Ber. 41. (1908) 4194. [7] T.C. Clark arid M.A.A. Clyne, Trans. Faraday Sot. 65 (1969) 2994. [S] C. P&lard, R. Mare& and J. Combourieu; dompt. Rend.Acad.Sci. (Parisj 264C (1967) 1721. [9] W. W. Rice, data being gathered toward Ph. D. dissertation.
CHEMICAL PHYSICS LETTERS
.
_
THERMALLY
Los Alamos
INITIATED
RF
CHEMICAL
15 January 1971
LASER
R. J. JENSEN and W. W. RICE * Scientific Lubomtory of the Unfversity of Califvku, Los Alamos,
New Mexico,. USA
Received 30 November 1970 The ClN explosion has been used to thermally decompose NF3 and SF into fluorine atoms which react with 4 2 producing HF laser action. The reaction of i3 ato:n on fluor Bne bearing species is indicated by 4-3IiF laser transitions.
HF laser action has been observed from the reaction of thermally decomposed gaseous fluorides with hydrogen. This thermal triggering of the laser producing chemical reaction is capable of quantitatively decomposing many gaseous fluorides as hdmogeneously as a flash lamp but with a much smaller electrical energy requirement. Fumermore, thermal triggering is not limited to prossure regimes in which an electric discharge can be pbtained. In this work a xenon flash lamp was used to trigger the explosion of ClN3 which was present in tertiary mixtures ClN3 +-NF3 + H2 and ClN3 + SF6 t H2. The compounds NF6 and SF6 are known to have very little optical absorption [1,2] in the spectral region of xenon flash lamps, and, indeed, the binary mixtures NF3 + H2 and SF6 + 22 could not be made to react by flash lamp initiation in this series of experiments. However, with 12-25 mole percent ClN3 added to these mixtures a sharp laser pulse was emitted. Pulsed RF laser oscillation from NFQ + H2 mixtures has prwioudy been reported by Gregg et al. [3]. The reaction in these mixtures was initiated by an electron beam, Electric discharge initiation of SF6 t Hi mixtures has been reported by Jensen and Rice [4]. Spencer et aL [5] have thermally decomposed SF6 to provide F atoms which when mixed with H2 produced laser oscillation in a flowing system. The present letter describes chemical laser action resulting from the thermal production of F atoms in premixed laser gases.
For this experiment a quartz laser tube 124
cm long and 21 mm in d&meter was fitted with scum chloride windows at the Brewster angle. The laser tube was positioned midway between * Supportedby Atomic ‘Energy Commision ‘andAsee ciated,Western Uqiversities graduate fellowship.
214 :
.
two totally reflecting,
gold surfaced mirrors of 10 m radius of curvature which were 202cm apart. A portion of the laser flux was reflected out of the cavity by slightly misaligned Brewster angle windows affording two convenient beams for monitoring the laser oscillation. The radiation reflected from one window was focused by a spherical mirror on a Philco GPC-215 Au:Ge detector., The reflection from the other window was focused on the entrance slits of a 0.5 m Jarrell Ash monochromator which was fitted with a Bausch and Lomb grating blazed at 9p. The HF rotation-vibration transitions were observed in third order using a Philco GPC-216 detector positioned at the exit slits of the monochromator. A Tektronix 555 dual beam oscilloscope followed the response from both detectors simultaneously. The oscilloscope was triggered by an RCA 929 vacuum photodiode monitoring the output of a 76 cm xenon flash lamp which was positioned against the laser tube to initiate
the CIN3 explosion.
The ClN3 was generated by the method of Raschig [6] (acidifying an aqueous solution containing equimolar concentrations of NaOCL and NaN$. The gases used were Air Products 9’7.5% minimum purity NF3, Allied Chemical 96% minimum purity SF6, and Linde- 99.99%minimum purity Ho. The chemicals used in the synthesis of GIN3 included MC&B practical grade NaN3, B.&I u.s.p. grade H3BO3, and B&A reagent grade NaCQ 5% solution. HaIocarhon 25-55 grease was used on all ground glass joints and stopcocks throughout the system. The ClN3 + NF3.+ H2 mi&ures were fired at
several molar ratios: 1 ClN311 NF3/6 H2, 1 ClN3/2 NF3/5 Hz, -2 ClN3/2 NF3/4 H2 and
3 CW~/l NF3/4 Hr The most successful results were obtained from the Jj1/2- ratio at pressures .betw&n 12 and 24 to+. The‘ laser..t&hsitions . ._
t Volume 3, number
2
CHEMICAL PHYSICS LETTERS orated
Tabie 1 HF laser lines observed in 3 2ClN3/2NF3/4H2 ratio mixture l-+0
2-l
3d2
4-3
p3 (5)
P4(5) P4@)
Pl@)
p2 (6)
p3 (6)
PlOO)
P2 (7)
p3 (7)
P2 (8)
p3 (8)
Pl (11)
molar
p2 (9)
P,(8)
TOTAL INITIAL
PRESSURE 16.3
TORR
P,(7)
from
the action
of F atoms
and XF,
only a
qualitative comparison of relative intensities carr be made. The pulse width on the upper trace is broader than the lower trace because a 1000 ohm resistor instead of a 51 ohm resistor was used to determine @e oscilloscope input. The full width of the HF pulse was between 0.5 and I lrsec and the peak power was two orders of magnitude greater than that of the HCL’lasers previously fired in the same optical cavity. A ClN3 + SF8 + H2 mixture at 24 mole percent ClN3, 19 mole percent SF6, and 57 mole percent H2 was also fired successfully. A major probLem with the SF6 system was that the reaction deposited an abundance of sulphur throughout the laser tube which necessitated swabbing the tube out between shots. The laser oscillation for this mixture exhibited the same type narrow, intense laser spike. The CINQ absorption spectrum [7] in the nearultraviolet overlaps the emission spectrum of the xenon flash lamp, so that the highly exothermic reaction
ClN3 + 12v-+C12 + 4 N2, AH = - 93.2 kcal “mole
TOTAL INITIAL
PRESSURE 15,8
TORR
P4(6)
is initiated, producing temperatures of several thousand degrees [8]. During the explosion of the tertiary mixtures, the NF3 or SF8 is substantially dissociated into F atoms allowing the reaction F + H2-+HF + H,
AH = -31.8 kcal/mole
TOTAL INITIAL
PRESSURE 13.1
TORR
(EA = 1.7 kcaljmole) FLASH LAEP
to populate the Oth, lst, 2nd and 3rd vibrational levels of HF (see table 2). It is interesting to Table 2
FLASH LAMP
Fig. 1. Laser emission fro? 2ClN3/2NF3/4H2 molar r.atio mixture. Time scale 1 psec/div., arbitrary intensity scale.
observed under these conditions are Listed in table 1. In fig. 1 an intense rotational-vibrational line. for several of the observed vIbrational transitions is shown along with.+te total laser-pulse. -Since the NaCl Brewster _windoFs rapidly deteri’
Energy needed for population of vibrationz&ly &cited states
Vibrational transition
Band origin in cm -1
Band origin
in kcnt/moIe
041
3961.6
11.3
o-2
7751.0
22.2
o-+3
11373.0
32.5
0 4.4
148i1.9
-
42.4
Volume 8,jumber .
2
‘_ 1
P (6) trax&ions seved. Bc”aus6 the %I2.4 kcal/mo!e’ populate the 4th jibratioti1 level of avai&ble in the-pr,&ceding.reaction; P4(6) transition& mu&be attributed note that P#).and
energetic reaction
-CHEMICALPHYsICS’iET’rERS
~.
were-&b:
:
required to HF are not the P&5) and -’ to tlie more :
R+N-F~((x~~)~HF+NF~_~, : AH =. -70 kcal/mole. From the authors’ prewious experience [g] with ClN3 in H3 containing systems HCXlaser lines would have been expected.. A scan of the lines Pz(6); 32(‘7) tid P2(8) of HCl showed that they were not present in this expegment.
REFERENCES
.. _ ..
:.
=.
.[I;.% FL LaPaglia and h.B. F. Duncan, _J,Cheti. Phys.
34 (1961) 1003. -[2]T.itl. &MoeandA.B.F.Duacaa. J.Chem.Phys. 19 (lxil) 71. 131 D.W. Gregg, B.Krawetz. R.K.Pears&, B.R. Schleicher, S.J.Thomas, E.B.Huss. K.J.Pettipiece, -J. R. Creighton.. Et.E. Niver and Y. L. Pan, UCRL Preprint-72434 (1970). [4] R. J..Jeensenand W. W. Rice, Chem. Phys. Letters 7 (1970) 627. [5] D. J.Spencer. H. Mirels. T. A. Jacobs and R.W. F. Gross, Appl. Phys. Letters 16 (1970) 235. [S] F. Raschig, Chem. Ber. 41. (1908) 4194. [7] T.C. Clark arid M.A.A. Clyne, Trans. Faraday Sot. 65 (1969) 2994. [S] C. P&lard, R. Mare& and J. Combourieu; dompt. Rend.Acad.Sci. (Parisj 264C (1967) 1721. [9] W. W. Rice, data being gathered toward Ph. D. dissertation.