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The H-NO chemiluminescence using adiabatically expanded NO
Volume 5. number 2
THE
H-NO
CHEnllCAL PHYSICSLETTERS
CHEMILUMINESCENCE D. GOLOMB.
USING
ADIABATICALLY
1 March
EXPANDED
19’70
NO
G. L. DYER and D. F. KITROSSER
Air Force Cambridge Reseat-cl1 Labovatouies. Bedford, Massachusetts 01730, USA
Received 20 November 1969 Pu’itricoxide has been expanded from a high-pressure reservoir against a supersonic stream of hydro-
gen atoms in an inert carrier. A chemiluminous headglow was observed in which the emission intensity exceeded by three orders of magnitude the intensity of the afterglow. The spectrum consists of the vibronic bands of the lA” - lA’ transition.
1. INTRODUCTION We reported previously on the intense headglow which results when adiabatically expanded nitric oxide is impinging upon atomic oxygen [l]. The enhanced light emission was postulated [a] and proven [3] to arise from an interaction of molecular clusters of NO with 0. In the NO - 0 reaction a third-body must be present to stabilize the excited electronic state from which emission occurs. In the cluster-atom collision, the third-body is conveniently carried along, eliminating the need for triple collisions:
(NO), + 0 - (NO),_1 + NO;,
NO;-N02thv. Inthis work we. shall
(1) 63
present evidence about the enhanced light emission in the NO - I-Iheadglow using adiabatically expanded NO. The NO - H titerglow has been studied previously in a flow system at 1 - 2 torr pressure by Clyne and Thrush [4]. 2. FXPERIME’NTAL The set-up was similar to the one described in ref. [l], except that hydrogen was dissociated in microwave cavities instead of oxygen. A mixture of 10% H2 - 90% A by volume, at a pressure of 10 torr, was passed through three paralleled discharge cavities into a settling chamber. There it was diluted 40-fold with nitrogen to a total plenum pressure of 200 mtorr. This mixture passed through a converging-diverging Mach 3.4
DeLaval nozzle into a 3 m test section of a wind tunnel. Against this supersonic stream of H - H2 - A - N2 mixture, a jet of NO FYELS impinging. The NO jet was released from an 1 mm orifice at 1 atm initial pressure. A Luminous headglow resulted as seen in fig. 1. The right emission intensity was measured in two manners. 1) With a silicon photocell located near the NO release orifice, viewing the glow from the inside with a circular field of view 14’ wide. 2) With a camera located outsidea window of the wind tunnel. The camera viewed the whole glow and recorded it on calibrated Kodak Tri-X film, using anJ’2 lens and 10 set exposure. The spectrum was obtained with a FastieEbert type 0.5 m spectrometer using an S-20 photocathode, also located outside a window_ A telephoto lens focussed the headglow onto the entrance slit. 3. CALIBRATION AND RESULTS The spectrometer, the photocell, and the film were all calibrated by exposure to an extended light source which in turn had an absolute spectral calibration by a secondary NBS standard_ The relative spectral intensity of the HNO heaclglow up to the instrument response limit (8000A) is presented in fig. 2. ft has been assumed, as discussed below, that the HNO glow emits twice the number of Bhotons over the total spectrum as up to the 7625A peak. From the photocell and film response to the light-box and headglow, respectively, and the relative spectral intensity distribution, we can estimate the emission rate of the glow. 101
Volume
CfE3WK7AL PEl’YXCS LETTERS
5. number 2
Fig. 1. Photo (right) and isodensigraph 3.1.
1 March 1970
(left) of FIN0 headglow.
Emission rate constant
The headglow emission rate constant is calculated for the overall process NO+Ht
HNO + hv,
although the actual mechanism is probably logous to eqs. (1) and (2). In such a fashion
HEADGLDY
a.01I. . . I .I Sma
I II I 6ooo
m
.
I I.
Fig. 2. Spectrum
I : I I I mmI I I I I I 7om
WPVELENGTH
fir
of IiNO headglow.
mm
(3) ana-
k is prorated for monomeric nitric oxide and expressed in cm3 molec-1 set-1. a) Photocell measurement. The photocell recorded an emission rate B= (0.6 *0.3)x1012 photons cm-2 (column)-l se&. The rate conetaA is obtained from
B =
k[NOlt [Hlt6 ,
where [NO4 and [Hit are the reactants concentration behmd the inner and outer shocks, respectively, and 8 is a characteristic thickness of the reaction zone. In separate wind tunnel experiments [5], it has been shown that d = 0.04 R,, where R, is the radius from the NO jet orifice to the maximum intensity contour of the headglow. From fig. 1 we measure R, = 12.7 cm, hence 6 = 0.5 cm. The total pressure behind the shocks was 50 mtorr, hence [NOIt = 1.7 x lo15 molec cm-3. Unfortunately, the hydrogen atom concentration was not determined directly in these experiments, however, Clyne and Thrush [4] found the dissociation yield of argon-hydrogen mixtures to be about 1%. This mixture constituted 2.56 of the total gas flowing through the DeLaval nozzle. Hence, [Hb 21 4 x 1011 atoms cm-3. Similar atom concentrations have been determined in experiments where oxygen was dissociated instead of hydrogen [l]. Thus, 0.6~10~~
k=
1.7x1o15x4x1o11x
0.5
= 1.75 x 10-15 cm3molec-1sec-1, with an uncertainty factor of three. b) Photographic measurement. The planimetric integration of the photons deposited on the film, as determined from the isodensigraph (fig. I), g ave the total emission rate P = 1.14 x 10 4 photons see-1. The rate constant IS obtained from P =
(51
RINoltPlt Y,
where the reaction volume V = 27r@(l-cost!) 0. Here cr is the half-angle of the glow as seen on the photo (=45’), R, is the radius and 6 is defined above. Thus, V = 150 cm9, and k=
cluster formation occurs [3]. Lower emission rates are expected for smaller podvalues.
(41
1.14x1014 1.7x1015x4x1011x1.5x102
= 1.1 x 10-15 cm3molec-1sec-1
3.2. Spectnrm The spectrum of the headglow (fig. 2) resembles the afterglow spectrum of CLyne and Thrush [4], although a few more vibronic bands are identifiable and the underlyIng continuum seems to be
stronger. The band identification is based on Bancroft, Hollas and Ramsay’s atlas [6] of the
IA” - IA’ electronic transition The presence of some weak bands beyond 575OA, corresponding to the dissociation energy of HNO into H(2S) and NO(2H) at 46.6 kc&‘mole-1 indicates that the er:cited molecule can be formed above the dissoci;rtion energy and exist long enough for emission to occur. Clyne and Thrush postulated that access to the 1~” state is gamed via the 3A” state, which is formed in the collision of the ground state species. However, Krauss [‘I] argues against the 3A” state as an important path for the population of the IA” state because according to molecular-
orbital calculations a potential barrier.
the 3A” state would also have
The presence of the (l,O, 0) - (1,0,O) transition in the spectrum indicates that transItions to higher vibrational levels of the ground state are also possible. For the purpose of calculating the emission rate constant, we assumed that the spectral intensity distribution is symmetrical about the (O,O, 0) - (0, 0,O) transition, and the total photon emission rate was taken as tice the rate till the 7625A peak The estimate of the emission rate constant Is predicated on this assumption. tt would be desirable
to determine
the actual
These experiments were carried out in the Aerospace Environmental Facilities of the Arnold Center in Tennessee. The participation of Messrs. D. L. Whitfield and E. D. Tidwell of
ARO, Inc. is gratefully achnowledged ,
which is in good agreement with the above value, considering the apprcarimatlons and experimental uncertainties. A representative value Is k = 1.5 x lo-l5 cm3molec’1sec’1. Thus, the HNO headglow emission rate constant is about 2000 times larger than the afterglow rate constant as reported by ClJme and Thrush [4]. Note that the headglow has been obtained with an NO jet released at initial conditions of pod = 76 torr cm, where maximum dimer and
spec-
tral distribution of the HNO headglow in the infrared.
We are
also indebted to Mr. R H. Johnson of Photo MetMass. for the densitometrics, Inc., L&n&on, ry, and to Drs. D. Freeman and D. Paulsen of AFCRL for constructive criticism of the manuscript. REFERENCES [l] F. P. DelGreco. D.Golomb. J. A. van der BUek. R. A. Caasanova and EL.E. Good. J. Chem. Phye. 44 (1966) 4349. [Z]
A. FontiJn and D E. Roener. J. Chem. Phys. 46 (1967) 3275.
Volume 5. number 2
CHEMICAL PHYSICS LETTERS
[3] D. Golomb and R. E. Good, J. Chem. Phys. 49 (1968) 4176. [4] M. A. A. Clyne and B.A. Thrush, Discussions Fara-
day
[5] R.
104
Sot.
33 (1962)139.
E. Good and J. A, F. Hill, Technical Report MC
1 March 1970
64-116-Rl. Mitbras Inc., Cambridge. IMass. (X366). [6] J. L. Bancroft, J. M. Hollas and D.A. Ramsay, Csn. J.Phys. 40 (1962) 322. [7J M. Krmss, J. Res. Natl. Bur. Std. T3A (1969) 131.
THE
H-NO
CHEnllCAL PHYSICSLETTERS
CHEMILUMINESCENCE D. GOLOMB.
USING
ADIABATICALLY
1 March
EXPANDED
19’70
NO
G. L. DYER and D. F. KITROSSER
Air Force Cambridge Reseat-cl1 Labovatouies. Bedford, Massachusetts 01730, USA
Received 20 November 1969 Pu’itricoxide has been expanded from a high-pressure reservoir against a supersonic stream of hydro-
gen atoms in an inert carrier. A chemiluminous headglow was observed in which the emission intensity exceeded by three orders of magnitude the intensity of the afterglow. The spectrum consists of the vibronic bands of the lA” - lA’ transition.
1. INTRODUCTION We reported previously on the intense headglow which results when adiabatically expanded nitric oxide is impinging upon atomic oxygen [l]. The enhanced light emission was postulated [a] and proven [3] to arise from an interaction of molecular clusters of NO with 0. In the NO - 0 reaction a third-body must be present to stabilize the excited electronic state from which emission occurs. In the cluster-atom collision, the third-body is conveniently carried along, eliminating the need for triple collisions:
(NO), + 0 - (NO),_1 + NO;,
NO;-N02thv. Inthis work we. shall
(1) 63
present evidence about the enhanced light emission in the NO - I-Iheadglow using adiabatically expanded NO. The NO - H titerglow has been studied previously in a flow system at 1 - 2 torr pressure by Clyne and Thrush [4]. 2. FXPERIME’NTAL The set-up was similar to the one described in ref. [l], except that hydrogen was dissociated in microwave cavities instead of oxygen. A mixture of 10% H2 - 90% A by volume, at a pressure of 10 torr, was passed through three paralleled discharge cavities into a settling chamber. There it was diluted 40-fold with nitrogen to a total plenum pressure of 200 mtorr. This mixture passed through a converging-diverging Mach 3.4
DeLaval nozzle into a 3 m test section of a wind tunnel. Against this supersonic stream of H - H2 - A - N2 mixture, a jet of NO FYELS impinging. The NO jet was released from an 1 mm orifice at 1 atm initial pressure. A Luminous headglow resulted as seen in fig. 1. The right emission intensity was measured in two manners. 1) With a silicon photocell located near the NO release orifice, viewing the glow from the inside with a circular field of view 14’ wide. 2) With a camera located outsidea window of the wind tunnel. The camera viewed the whole glow and recorded it on calibrated Kodak Tri-X film, using anJ’2 lens and 10 set exposure. The spectrum was obtained with a FastieEbert type 0.5 m spectrometer using an S-20 photocathode, also located outside a window_ A telephoto lens focussed the headglow onto the entrance slit. 3. CALIBRATION AND RESULTS The spectrometer, the photocell, and the film were all calibrated by exposure to an extended light source which in turn had an absolute spectral calibration by a secondary NBS standard_ The relative spectral intensity of the HNO heaclglow up to the instrument response limit (8000A) is presented in fig. 2. ft has been assumed, as discussed below, that the HNO glow emits twice the number of Bhotons over the total spectrum as up to the 7625A peak. From the photocell and film response to the light-box and headglow, respectively, and the relative spectral intensity distribution, we can estimate the emission rate of the glow. 101
Volume
CfE3WK7AL PEl’YXCS LETTERS
5. number 2
Fig. 1. Photo (right) and isodensigraph 3.1.
1 March 1970
(left) of FIN0 headglow.
Emission rate constant
The headglow emission rate constant is calculated for the overall process NO+Ht
HNO + hv,
although the actual mechanism is probably logous to eqs. (1) and (2). In such a fashion
HEADGLDY
a.01I. . . I .I Sma
I II I 6ooo
m
.
I I.
Fig. 2. Spectrum
I : I I I mmI I I I I I 7om
WPVELENGTH
fir
of IiNO headglow.
mm
(3) ana-
k is prorated for monomeric nitric oxide and expressed in cm3 molec-1 set-1. a) Photocell measurement. The photocell recorded an emission rate B= (0.6 *0.3)x1012 photons cm-2 (column)-l se&. The rate conetaA is obtained from
B =
k[NOlt [Hlt6 ,
where [NO4 and [Hit are the reactants concentration behmd the inner and outer shocks, respectively, and 8 is a characteristic thickness of the reaction zone. In separate wind tunnel experiments [5], it has been shown that d = 0.04 R,, where R, is the radius from the NO jet orifice to the maximum intensity contour of the headglow. From fig. 1 we measure R, = 12.7 cm, hence 6 = 0.5 cm. The total pressure behind the shocks was 50 mtorr, hence [NOIt = 1.7 x lo15 molec cm-3. Unfortunately, the hydrogen atom concentration was not determined directly in these experiments, however, Clyne and Thrush [4] found the dissociation yield of argon-hydrogen mixtures to be about 1%. This mixture constituted 2.56 of the total gas flowing through the DeLaval nozzle. Hence, [Hb 21 4 x 1011 atoms cm-3. Similar atom concentrations have been determined in experiments where oxygen was dissociated instead of hydrogen [l]. Thus, 0.6~10~~
k=
1.7x1o15x4x1o11x
0.5
= 1.75 x 10-15 cm3molec-1sec-1, with an uncertainty factor of three. b) Photographic measurement. The planimetric integration of the photons deposited on the film, as determined from the isodensigraph (fig. I), g ave the total emission rate P = 1.14 x 10 4 photons see-1. The rate constant IS obtained from P =
(51
RINoltPlt Y,
where the reaction volume V = 27r@(l-cost!) 0. Here cr is the half-angle of the glow as seen on the photo (=45’), R, is the radius and 6 is defined above. Thus, V = 150 cm9, and k=
cluster formation occurs [3]. Lower emission rates are expected for smaller podvalues.
(41
1.14x1014 1.7x1015x4x1011x1.5x102
= 1.1 x 10-15 cm3molec-1sec-1
3.2. Spectnrm The spectrum of the headglow (fig. 2) resembles the afterglow spectrum of CLyne and Thrush [4], although a few more vibronic bands are identifiable and the underlyIng continuum seems to be
stronger. The band identification is based on Bancroft, Hollas and Ramsay’s atlas [6] of the
IA” - IA’ electronic transition The presence of some weak bands beyond 575OA, corresponding to the dissociation energy of HNO into H(2S) and NO(2H) at 46.6 kc&‘mole-1 indicates that the er:cited molecule can be formed above the dissoci;rtion energy and exist long enough for emission to occur. Clyne and Thrush postulated that access to the 1~” state is gamed via the 3A” state, which is formed in the collision of the ground state species. However, Krauss [‘I] argues against the 3A” state as an important path for the population of the IA” state because according to molecular-
orbital calculations a potential barrier.
the 3A” state would also have
The presence of the (l,O, 0) - (1,0,O) transition in the spectrum indicates that transItions to higher vibrational levels of the ground state are also possible. For the purpose of calculating the emission rate constant, we assumed that the spectral intensity distribution is symmetrical about the (O,O, 0) - (0, 0,O) transition, and the total photon emission rate was taken as tice the rate till the 7625A peak The estimate of the emission rate constant Is predicated on this assumption. tt would be desirable
to determine
the actual
These experiments were carried out in the Aerospace Environmental Facilities of the Arnold Center in Tennessee. The participation of Messrs. D. L. Whitfield and E. D. Tidwell of
ARO, Inc. is gratefully achnowledged ,
which is in good agreement with the above value, considering the apprcarimatlons and experimental uncertainties. A representative value Is k = 1.5 x lo-l5 cm3molec’1sec’1. Thus, the HNO headglow emission rate constant is about 2000 times larger than the afterglow rate constant as reported by ClJme and Thrush [4]. Note that the headglow has been obtained with an NO jet released at initial conditions of pod = 76 torr cm, where maximum dimer and
spec-
tral distribution of the HNO headglow in the infrared.
We are
also indebted to Mr. R H. Johnson of Photo MetMass. for the densitometrics, Inc., L&n&on, ry, and to Drs. D. Freeman and D. Paulsen of AFCRL for constructive criticism of the manuscript. REFERENCES [l] F. P. DelGreco. D.Golomb. J. A. van der BUek. R. A. Caasanova and EL.E. Good. J. Chem. Phye. 44 (1966) 4349. [Z]
A. FontiJn and D E. Roener. J. Chem. Phys. 46 (1967) 3275.
Volume 5. number 2
CHEMICAL PHYSICS LETTERS
[3] D. Golomb and R. E. Good, J. Chem. Phys. 49 (1968) 4176. [4] M. A. A. Clyne and B.A. Thrush, Discussions Fara-
day
[5] R.
104
Sot.
33 (1962)139.
E. Good and J. A, F. Hill, Technical Report MC
1 March 1970
64-116-Rl. Mitbras Inc., Cambridge. IMass. (X366). [6] J. L. Bancroft, J. M. Hollas and D.A. Ramsay, Csn. J.Phys. 40 (1962) 322. [7J M. Krmss, J. Res. Natl. Bur. Std. T3A (1969) 131.