- Email: [email protected]
Laboratory measurement of the rate of the reaction N2+ + O → NO+ + N at thermal energy
Planet. Space Sci. 1965. Vol. 13. pp. 823 to 827. Pergmon
Press Ltd. Printed in Northern Ireland
LABORATORY MEASUREMENT OF THE RATE OF THE REACTION N,+ + 0 - NO+ + N AT THERMAL ENERGY E. E. FERGUSON, F. C. FEHSENFELD, P. D. GOLDAN A. L. SCHhJELTEKOPF and H. I. SCHIFF*
Central Radio Propagation Laboratory, National Bureau of Standards, Boulder, Colorado (Received 30 March 1965) Abstract-The rate coefficient for the reaction Nz+ + 0 + NO+ + N at 300°K has been measured to be k,, = 2.5(+1) x lo-lo cma see-‘. No previous laboratory measurements of this reaction rate at thermal energies have been reported. This reaction clearly plays an important role in the E- and FZ-regions of the ionosphere, accounting for significant NZ+ loss, outweighing the Nz+ loss rate with molecular oxygen. INTRODUCTION
Rates for several thermal ion-molecule reactions of ionospheric interest have recently been measured in this laboratory,(1-3) involving reactions between either an atomic or molecular ion and a stabIe molecular species (0, or N,). The details of construction and operation of the steady state flowing afterglow system, along with some measured rates of non-atmospheric reactions are being reported elsewhere.(4) The system has now been utilized to study a reaction involving two unstable (ground state) reactants N,+(X%;,+) + 0(3P) ---f NO+(XlX+) + N + 3.05 eV (la) and NZ+(X2E;,+) + 0(3P) --t N.JA?E;,+) + 0+(4S) + l-96 eV (lb) EXPERIMENTAL
N, is added to a fast flowing stream (u forming
N2+ in Penning
ionization
by helium
lo4 cm/set) of weakly ionized metastables,
He(23S) + N2 ---f He + Nz+ + e,
helium plasma,
(2)
the N2+ being formed in electronic states which radiate by allowed transitions into the ground electronic state. Recent absolute intensity spectroscopic measurements@) have shown that over 50 per cent of the N,+ ions radiate into the zeroth vibrational level of the ground electronic state, the strongest radiation being the 3914 A O-O transition of the 1st negative system, B2Eu+ -+ X2&+. The 0 atoms are produced by partial titration with the fast reaction@) N+NO+N,+O,
(3)
the N atoms being first formed by a microwave discharge in N,. The 0 atoms are introduced -30 cm downstream of the position where the Nz+ ions are formed. The NO flow was measured with a flow meter and was taken to be equal to the 0 atom flow. A schematic diagram of the apparatus is shown in Fig. 1. Oxygen atom recombination was experimentally determined to be negligible by measuring the reaction rate several ways. In * Permanent address: York University, Toronto, Canada. 7
823
824
E. E. FERGUSON
et al.
early experiments, the 0 atoms were introduced through a nozzle which had a constriction, a right angle bend, and several exit holes of -_8 mm diameter. Later, a straight tube of 11 mm i.d. and 30 cm length from the NO titration chamber was used. The rates for reaction 1 were the same with these two conditions where wall recombination would be expected to be quite different. This is consistent with the low probability (~10~) of 0 atom recombination”) on a glass surface. (No more than a few per cent 0 atom recombination is calculated to occur, using this probability.)
N
DISCHARGE
NO
N2
PUMP
0
f He
>dga
He
M
J I-
QUADRUPOLE
N2+
MASS
SPECTROMETER
FIG. 1. A SCHEMATIC DIAGRAMOF THESTEADYSTATEAFI-ERGLOW SYSTEM.
The ion products are sampled about 40 cm (~4 msec) from the downstream 0 atom introduction point with a quadrupole mass spectrometer. A serious experimental difficulty not present in earlier measurements(1’2) was encountered upon introduction of the oxygen atoms into the system, namely a large decrease in ion sampling efficiency. This appears to be due to a surface charging phenomenon and was finally alleviated by painting the surface of the sampling plate with a dispersion of colloidal graphite in alcohol.(s) The reaction rate is determined from the slope of the log N,f ion current curve against 0 atom concentration. The N,+ ions are converted nearly quantitatively into NO+ ions. No significant O+, O,+ or impurity ion currents were observed, under a considerable range of operating conditions. An appreciable N+ signal was observed, the Nf being produced by the fast reaction(l) He++N,+He+N+N+ (4) The low Of signal precludes reaction (lb) from being nearly as fast as (la) even though Of ions formed by reaction (1 b) would be converted to NO+ by the reaction O++N,+NO++N
(5) for which the measured ratec2) is k5 = 3 x lo-l2 cm3 see-l. There is necessarily a concentration of N, in the system, both from the N, added to supply the N2+ source (reaction 2) and the N, added to supply the N atom (and consequently 0 atom) source (reaction 3). Under conditions of minimum N, addition, ((O-5 atm cm3/sec, corresponding to 2.2 x 1013 N, molecules/cm3) the conversion of O+ formed by (lb) to NO+ should be less than 25 per cent. The O+ signal is so small in this experiment, that no evidence was obtained for the occurrence of reaction( 1b).
RATE
825
OF N,++O-NO++N
The normal operation of the reaction tube involved a steady microwave discharge in the helium used to produce Ns+ by reaction (2). Since photoionization of Na by the helium discharge also occurred, the experiment was repeated with the helium discharge pulsed. The ion detection was gated in such a manner that the delay between pulses prevented detection of N,+ photoions. This increased the measured reaction rate by a factor two. Direct oscilloscope display of the N2+ signal as a function of time after discharge pulse did indeed show a significant Ns+ signal produced by photoionization between the 0 atom addition jet and the quadrupole mass spectrometer sampling port.
I
I 0
I 0.2
I
I 0.4
I
I 0.6
NO flow, atm cm*/sec FIG.~.
THIS
FIGURESHOWSTHERESULTINGIONCURRENTSASAFUNCI~ONOFADDED
[O].
The resulting ion currents as a function of NO flow (and therefore 0 atom concentration) are shown in Fig. 2, taken with pulsed operation. The curvature in the Ns+ data may be due to a diffusion problem. The reported uncertainty of the rate constant is therefore made large enough to encompass all possible rates consistent with the data. The NO+ signal increase very nearly balances the N,+ signal loss as it should. We do not interpret the N+ signal loss at this time, but have good reason to believe it does not affect the Ns+ reaction measurement (see Note added in proof (1)). Since the N atom concentration varies with the extent of the partial titration (the amount of NO added to the nitrogen afterglow), it is necessary to argue that the charge-transfer N,+ + N -+ N, + Nf is much slower than reaction (1). This is verified experimentally by simply turning off the downstream microwave discharge which produces the nitrogen atoms. No significant change in the Nz+ signal is caused by this. Since the N atom concentration equals the maximum 0 atom concentration, this establishes the above point. RESULT?3
The resulting ion currents as a function of added NO and therefore 0 atom concentration are shown in Fig. 2. The resulting rate constant is k,, = 2-S (f 1) x lo-lo cm3/sec at 300°K. k,, is less than lo-l1 cm3/sec.
826
E. E. FERGUSON
et al.
DISCUSSION
Reaction (la) is only exothermic into the ground state of NO+. Most atmospheric physicists have not used reaction (la) because of a theoretical argument that NO+ could only be formed efficiently from N,f and 0 into an excited state of NO+ which could be formed from an N+ ion and an 0 atom. w The lowest such state available, 3A, is 16.55 eV above the NO PIl ground state and this requirement would then make the ion-atom interchange reaction between Nsf and 0 endothermic. The argument against reaction (la) has not always been considered compelling. (11) Reaction (1b) is theoretically unlikely to be rapid. For N,(XlE;,+) formed in the ground vibrational state, the reaction is very far off resonance (“2 eV) and at thermal energies would be adiabatic and hence extremely inefficient. In order to get a near energy resonance, the Ns would need to be produced in z, = 7. In this case the Franck-Condon factor is rather small,(l”) which would seem to weigh against this possibility. In ionospheric models (la) has been used by Norton, Van Zandt, and Denison.u2) From purely ionospheric considerations they inferred that the rate constant k,, must be greater than or equal to 2 x lo-l1 cm3 sec- l. The greater values of k,, would correspond to smaller concentrations of 0 and N 2+. If the recent measurements of these quantities by Hinteregger, Hall and Schmidtke, (13)Nier, Hoffman, Johnson and Holmes(14) and Holmes, Johnson and Youngus) are used in their model, the extreme limits on ki, are found to be 0.3 to 3-O X lo-lo cm3 se&. The importance of the non-negligible loss rate of N,+ with 0 atoms is of particular significance in view of the recent finding t2) that the rate for the reaction N,++O,+Oz++N,
(6)
ks = 4 x lo-l3 cm3 se&, is much lower than previously measured (see Note added in proof (2)). R e a c t ion (la) can now be invoked to explain the observation that N,+ concen-
trations are invariably observed to be small, smaller apparently than can be accounted for simply by dissociative recombination of N, f. Since k,, > k6,‘and [0] > [O,] in the E- and F-region, it is clear that atomic oxygen collisions dominate the reactive loss of N,+. It is of interest, that the Norton, Van Zandt and DenisorP2) model atmosphere did not invoke reaction (6). In a recent detailed examination of the NRL ionospheric positive ion data,u5) in conjunction with our previously reported rates for reaction (5) and (6), Donahueu6) has also pointed out that reaction (la) must be rapid from purely ionospheric considerations. Indeed, he finds the rate k,, should be larger than 5 x lo-lo cm3/sec at 300”K, somewhat larger than we measure. Zipf and Fastie (17)utilized a fairly large rate (6 x lo-l1 cms/sec) for N2+ loss with atomic oxygen, in order to explain their rocket dayglow observations of the intensity of the (0,O) 1st negative band of Ns+ between 100 and 223 km. Their interpretation also involved a large rate constant for N, + loss with molecular oxygen, k, = 2 x lo-lo cms/sec however. More recently, Zipf us) has reviewed the current status of rocket measurements of the visible dayglow in the light of recent rocket data and new laboratory results. He finds that with the large rate constant for N, + loss with O,, k, = 2 x lo-lo cm3/sec, the rate constant for Nz+ + 0 reaction, k,, + k,, = 5 x lo-l1 cm3/sec with no appreciable temperature dependence, whereas with ks = 4 x lo-l3 cm3/sec, k,, + k,, = 2.3 x lo-lo cm’/sec at 300 “K with a strong temperature dependence. This latter result is in remarkable agreement with the present measurement of k,, + k,, = 2.5 x lo-lo cms/sec and the previous
RATE OF N,+ +O-+NO++N
827
measurement of k, = 4 x lo-l3 cm3/sec in this laboratory. The present measurement of k,, + k,, is not sufficiently precise however to distinguish between the high and low rates for k6 by comparison with Zipf’s analysis. Zipf’s analysis emphasizes the importance of temperature dependence studies for this ion-neutral reaction rate. Instrumentation for such measurements is being constructed in this laboratory. Notes added in proof (1) Subsequent experiments have removed the curvature in the N 2+ versus NO curve, giving a linear decrease of the N,+ signal over one order of magnitude. The resulting slope yields kI, = 2.5 x lo-l0 cm3/sec as reported here. The N+ signal loss is probably due to reaction of N+ with the Oz which is formed by 0 atom recombination. Since the reaction of N+ with Oa has a rate constant four times larger than the Na+ + 0 reaction (reference(2)), the smaller N+ decrease verifies the conclusion that the extent of oxygen atom recombination is small. (2) The low rate constant reported for reaction (6) has been found to be erroneous. A subsequent measurement gives k, = 1.0 (f0.5) x lo-lo cms/sec removing all laboratory ambiguity over this rate constant. A correction is to be published [F. C. FEHSENFELD, A. L. SCHMELTEKOPF and E. E. FERGUSON, Planet. Space Sci.]. This does not alter the argument that reaction (la) is the main N,+ loss process in the E- and Fl-regions of the ionosphere. It can now be shown that the positive ion-neutral rate constants measured in the laboratory are in satisfactoryagreementwith daytime, equilibriumionosphericrequirements in the E- and FI-regions [E. E. FERGUSON,F. C. FEHSENFELD, P. D. GOLDANand A. L. SCHMELTEKOPF, J. Geophys. Rex submitted].
Acknowledgements-The authors have benefited from discussions with T. E. Van Zandt and R. B. Norton. This work has been supported in part by the Defence Atomic Support Agency (DASA). REFERENCES 1. E. E. FERGUSON,F. C. FEHSENFELD, D. B. DUNKIN, A. L. SCHMELTEKOPF and H. I. SCHIFF,Planet. Space Sci. 12, 1169 (1964). 2. F. C. FEHSENFELD, A. L. SCHMELTEKOPF and E. E. FERGUSON, Planet. Space Sci. 13,219 (1965). 3. F. C. FEHSENFELD, P. D. GOLDAN, A. L. SCHMELTEKOPF and E. E. FERGUSON, PIanet. Space Sci. 13, 579. 4. F. C. FEHSENFELD, A. L. SCHMELTEKOPF, H. I. SCHIFFand E. E. FERGUSON, to be published. 5. A. L. SCHMELTEKOPF, P. D. GOLDAN,F. C. FEHSENFELD and E. E. FERGUSON, to be published. 6. L. F. PHILLIPSand fi. I. SCHIFF,J. Chem. Phys. 36, 1509 (1962). 7. J. W. LINNE~ and D. G. H. MARSDEN.Proc. Rov. Sot.. Load. A234.489 (1956). , . I ’ 8. E. LINDHOLM,Rev. Sci. Instrum. 31,21b (1960). ’ 9. D. R. BATESand M. NICOLET,J. Atmos. Terr. Phys. 18, 65 (1960). 1Oa. F. R. GILMORE,Memorandum RM-4034-PR, The Rand Corp., Santa Monica, California, June 1964. lob. F. R. GILMORE,J. Quant. Spect. Rad. Transfer 5,369 (1965). 11. A. DALGARNOand j. C. G.-WALKER, J. Atmos. Sci. Zi, 46j (1964). 12. R. B. NORTON.T. E. VAN ZANDTand J. S. DENISON.Proceedinps on the ” of J the International Conference J
13. 14. 15. 16. 17. 18.
Zonosphere, p.26. London (1963). H. E. HINTEREGGER, L. A. HALL and G. SCHMLDTKE, Space Research V. North Holland, Amsterdam. A. 0. NIER, J. H. HOFFMAN,C. Y. JOHNSONand J. C. HOLMES,J. Geophys. Res. 69,979 (1964). J. C. HOLMES,C. Y. JOHNSONand J. M. YOUNG, Space Research V. North Holland, Amsterdam. T. M. DONAHUE,Planet. Space Sci., in press. E. C. ZIPF and W. G. FASTIE,J. Geophys. Res. 69,2357 (1964). E. C. ZIPF, J. Geomagn. Geoelect., in press. H3ME!PeHHRM, H03+$lBQHeHT CKOPOCTIl AJIH peaK9ZfH N,+ + 0 ---, NO+ +N, Ha 300°K, oKaaaacH kla = 2.5( fl) x 10-lo~~* ceK-I. CooBnIeHni o KaKnxnnGo npemnllx na60paTopHbrx H3MepemGI 3~oP peaHqHH np~ TepMn4ecKHx aHeprMsx, ~0 c~lx IlOp He llOCTyllHJlO. 3Ta pEiK~I0-I HeCOMHt?HHO EiI’paCT BaxHyIO POJIb B CJIOIIX EIOHOC@PbI i?i? mF 1, FIBJE=IRCb OTBeTCTBeHHOti 38 3HEFIHTeJlbHJ’IO nOTepI Na+ Ii 33 IIt?peB&?lIIHBaHHe CKOPOCTZi IIOTepn Nz+ MOllf%yJr~pHblM K~CJlOpO~OM.
Pe3IOMe--CONIaCHO
Press Ltd. Printed in Northern Ireland
LABORATORY MEASUREMENT OF THE RATE OF THE REACTION N,+ + 0 - NO+ + N AT THERMAL ENERGY E. E. FERGUSON, F. C. FEHSENFELD, P. D. GOLDAN A. L. SCHhJELTEKOPF and H. I. SCHIFF*
Central Radio Propagation Laboratory, National Bureau of Standards, Boulder, Colorado (Received 30 March 1965) Abstract-The rate coefficient for the reaction Nz+ + 0 + NO+ + N at 300°K has been measured to be k,, = 2.5(+1) x lo-lo cma see-‘. No previous laboratory measurements of this reaction rate at thermal energies have been reported. This reaction clearly plays an important role in the E- and FZ-regions of the ionosphere, accounting for significant NZ+ loss, outweighing the Nz+ loss rate with molecular oxygen. INTRODUCTION
Rates for several thermal ion-molecule reactions of ionospheric interest have recently been measured in this laboratory,(1-3) involving reactions between either an atomic or molecular ion and a stabIe molecular species (0, or N,). The details of construction and operation of the steady state flowing afterglow system, along with some measured rates of non-atmospheric reactions are being reported elsewhere.(4) The system has now been utilized to study a reaction involving two unstable (ground state) reactants N,+(X%;,+) + 0(3P) ---f NO+(XlX+) + N + 3.05 eV (la) and NZ+(X2E;,+) + 0(3P) --t N.JA?E;,+) + 0+(4S) + l-96 eV (lb) EXPERIMENTAL
N, is added to a fast flowing stream (u forming
N2+ in Penning
ionization
by helium
lo4 cm/set) of weakly ionized metastables,
He(23S) + N2 ---f He + Nz+ + e,
helium plasma,
(2)
the N2+ being formed in electronic states which radiate by allowed transitions into the ground electronic state. Recent absolute intensity spectroscopic measurements@) have shown that over 50 per cent of the N,+ ions radiate into the zeroth vibrational level of the ground electronic state, the strongest radiation being the 3914 A O-O transition of the 1st negative system, B2Eu+ -+ X2&+. The 0 atoms are produced by partial titration with the fast reaction@) N+NO+N,+O,
(3)
the N atoms being first formed by a microwave discharge in N,. The 0 atoms are introduced -30 cm downstream of the position where the Nz+ ions are formed. The NO flow was measured with a flow meter and was taken to be equal to the 0 atom flow. A schematic diagram of the apparatus is shown in Fig. 1. Oxygen atom recombination was experimentally determined to be negligible by measuring the reaction rate several ways. In * Permanent address: York University, Toronto, Canada. 7
823
824
E. E. FERGUSON
et al.
early experiments, the 0 atoms were introduced through a nozzle which had a constriction, a right angle bend, and several exit holes of -_8 mm diameter. Later, a straight tube of 11 mm i.d. and 30 cm length from the NO titration chamber was used. The rates for reaction 1 were the same with these two conditions where wall recombination would be expected to be quite different. This is consistent with the low probability (~10~) of 0 atom recombination”) on a glass surface. (No more than a few per cent 0 atom recombination is calculated to occur, using this probability.)
N
DISCHARGE
NO
N2
PUMP
0
f He
>dga
He
M
J I-
QUADRUPOLE
N2+
MASS
SPECTROMETER
FIG. 1. A SCHEMATIC DIAGRAMOF THESTEADYSTATEAFI-ERGLOW SYSTEM.
The ion products are sampled about 40 cm (~4 msec) from the downstream 0 atom introduction point with a quadrupole mass spectrometer. A serious experimental difficulty not present in earlier measurements(1’2) was encountered upon introduction of the oxygen atoms into the system, namely a large decrease in ion sampling efficiency. This appears to be due to a surface charging phenomenon and was finally alleviated by painting the surface of the sampling plate with a dispersion of colloidal graphite in alcohol.(s) The reaction rate is determined from the slope of the log N,f ion current curve against 0 atom concentration. The N,+ ions are converted nearly quantitatively into NO+ ions. No significant O+, O,+ or impurity ion currents were observed, under a considerable range of operating conditions. An appreciable N+ signal was observed, the Nf being produced by the fast reaction(l) He++N,+He+N+N+ (4) The low Of signal precludes reaction (lb) from being nearly as fast as (la) even though Of ions formed by reaction (1 b) would be converted to NO+ by the reaction O++N,+NO++N
(5) for which the measured ratec2) is k5 = 3 x lo-l2 cm3 see-l. There is necessarily a concentration of N, in the system, both from the N, added to supply the N2+ source (reaction 2) and the N, added to supply the N atom (and consequently 0 atom) source (reaction 3). Under conditions of minimum N, addition, ((O-5 atm cm3/sec, corresponding to 2.2 x 1013 N, molecules/cm3) the conversion of O+ formed by (lb) to NO+ should be less than 25 per cent. The O+ signal is so small in this experiment, that no evidence was obtained for the occurrence of reaction( 1b).
RATE
825
OF N,++O-NO++N
The normal operation of the reaction tube involved a steady microwave discharge in the helium used to produce Ns+ by reaction (2). Since photoionization of Na by the helium discharge also occurred, the experiment was repeated with the helium discharge pulsed. The ion detection was gated in such a manner that the delay between pulses prevented detection of N,+ photoions. This increased the measured reaction rate by a factor two. Direct oscilloscope display of the N2+ signal as a function of time after discharge pulse did indeed show a significant Ns+ signal produced by photoionization between the 0 atom addition jet and the quadrupole mass spectrometer sampling port.
I
I 0
I 0.2
I
I 0.4
I
I 0.6
NO flow, atm cm*/sec FIG.~.
THIS
FIGURESHOWSTHERESULTINGIONCURRENTSASAFUNCI~ONOFADDED
[O].
The resulting ion currents as a function of NO flow (and therefore 0 atom concentration) are shown in Fig. 2, taken with pulsed operation. The curvature in the Ns+ data may be due to a diffusion problem. The reported uncertainty of the rate constant is therefore made large enough to encompass all possible rates consistent with the data. The NO+ signal increase very nearly balances the N,+ signal loss as it should. We do not interpret the N+ signal loss at this time, but have good reason to believe it does not affect the Ns+ reaction measurement (see Note added in proof (1)). Since the N atom concentration varies with the extent of the partial titration (the amount of NO added to the nitrogen afterglow), it is necessary to argue that the charge-transfer N,+ + N -+ N, + Nf is much slower than reaction (1). This is verified experimentally by simply turning off the downstream microwave discharge which produces the nitrogen atoms. No significant change in the Nz+ signal is caused by this. Since the N atom concentration equals the maximum 0 atom concentration, this establishes the above point. RESULT?3
The resulting ion currents as a function of added NO and therefore 0 atom concentration are shown in Fig. 2. The resulting rate constant is k,, = 2-S (f 1) x lo-lo cm3/sec at 300°K. k,, is less than lo-l1 cm3/sec.
826
E. E. FERGUSON
et al.
DISCUSSION
Reaction (la) is only exothermic into the ground state of NO+. Most atmospheric physicists have not used reaction (la) because of a theoretical argument that NO+ could only be formed efficiently from N,f and 0 into an excited state of NO+ which could be formed from an N+ ion and an 0 atom. w The lowest such state available, 3A, is 16.55 eV above the NO PIl ground state and this requirement would then make the ion-atom interchange reaction between Nsf and 0 endothermic. The argument against reaction (la) has not always been considered compelling. (11) Reaction (1b) is theoretically unlikely to be rapid. For N,(XlE;,+) formed in the ground vibrational state, the reaction is very far off resonance (“2 eV) and at thermal energies would be adiabatic and hence extremely inefficient. In order to get a near energy resonance, the Ns would need to be produced in z, = 7. In this case the Franck-Condon factor is rather small,(l”) which would seem to weigh against this possibility. In ionospheric models (la) has been used by Norton, Van Zandt, and Denison.u2) From purely ionospheric considerations they inferred that the rate constant k,, must be greater than or equal to 2 x lo-l1 cm3 sec- l. The greater values of k,, would correspond to smaller concentrations of 0 and N 2+. If the recent measurements of these quantities by Hinteregger, Hall and Schmidtke, (13)Nier, Hoffman, Johnson and Holmes(14) and Holmes, Johnson and Youngus) are used in their model, the extreme limits on ki, are found to be 0.3 to 3-O X lo-lo cm3 se&. The importance of the non-negligible loss rate of N,+ with 0 atoms is of particular significance in view of the recent finding t2) that the rate for the reaction N,++O,+Oz++N,
(6)
ks = 4 x lo-l3 cm3 se&, is much lower than previously measured (see Note added in proof (2)). R e a c t ion (la) can now be invoked to explain the observation that N,+ concen-
trations are invariably observed to be small, smaller apparently than can be accounted for simply by dissociative recombination of N, f. Since k,, > k6,‘and [0] > [O,] in the E- and F-region, it is clear that atomic oxygen collisions dominate the reactive loss of N,+. It is of interest, that the Norton, Van Zandt and DenisorP2) model atmosphere did not invoke reaction (6). In a recent detailed examination of the NRL ionospheric positive ion data,u5) in conjunction with our previously reported rates for reaction (5) and (6), Donahueu6) has also pointed out that reaction (la) must be rapid from purely ionospheric considerations. Indeed, he finds the rate k,, should be larger than 5 x lo-lo cm3/sec at 300”K, somewhat larger than we measure. Zipf and Fastie (17)utilized a fairly large rate (6 x lo-l1 cms/sec) for N2+ loss with atomic oxygen, in order to explain their rocket dayglow observations of the intensity of the (0,O) 1st negative band of Ns+ between 100 and 223 km. Their interpretation also involved a large rate constant for N, + loss with molecular oxygen, k, = 2 x lo-lo cms/sec however. More recently, Zipf us) has reviewed the current status of rocket measurements of the visible dayglow in the light of recent rocket data and new laboratory results. He finds that with the large rate constant for N, + loss with O,, k, = 2 x lo-lo cm3/sec, the rate constant for Nz+ + 0 reaction, k,, + k,, = 5 x lo-l1 cm3/sec with no appreciable temperature dependence, whereas with ks = 4 x lo-l3 cm3/sec, k,, + k,, = 2.3 x lo-lo cm’/sec at 300 “K with a strong temperature dependence. This latter result is in remarkable agreement with the present measurement of k,, + k,, = 2.5 x lo-lo cms/sec and the previous
RATE OF N,+ +O-+NO++N
827
measurement of k, = 4 x lo-l3 cm3/sec in this laboratory. The present measurement of k,, + k,, is not sufficiently precise however to distinguish between the high and low rates for k6 by comparison with Zipf’s analysis. Zipf’s analysis emphasizes the importance of temperature dependence studies for this ion-neutral reaction rate. Instrumentation for such measurements is being constructed in this laboratory. Notes added in proof (1) Subsequent experiments have removed the curvature in the N 2+ versus NO curve, giving a linear decrease of the N,+ signal over one order of magnitude. The resulting slope yields kI, = 2.5 x lo-l0 cm3/sec as reported here. The N+ signal loss is probably due to reaction of N+ with the Oz which is formed by 0 atom recombination. Since the reaction of N+ with Oa has a rate constant four times larger than the Na+ + 0 reaction (reference(2)), the smaller N+ decrease verifies the conclusion that the extent of oxygen atom recombination is small. (2) The low rate constant reported for reaction (6) has been found to be erroneous. A subsequent measurement gives k, = 1.0 (f0.5) x lo-lo cms/sec removing all laboratory ambiguity over this rate constant. A correction is to be published [F. C. FEHSENFELD, A. L. SCHMELTEKOPF and E. E. FERGUSON, Planet. Space Sci.]. This does not alter the argument that reaction (la) is the main N,+ loss process in the E- and Fl-regions of the ionosphere. It can now be shown that the positive ion-neutral rate constants measured in the laboratory are in satisfactoryagreementwith daytime, equilibriumionosphericrequirements in the E- and FI-regions [E. E. FERGUSON,F. C. FEHSENFELD, P. D. GOLDANand A. L. SCHMELTEKOPF, J. Geophys. Rex submitted].
Acknowledgements-The authors have benefited from discussions with T. E. Van Zandt and R. B. Norton. This work has been supported in part by the Defence Atomic Support Agency (DASA). REFERENCES 1. E. E. FERGUSON,F. C. FEHSENFELD, D. B. DUNKIN, A. L. SCHMELTEKOPF and H. I. SCHIFF,Planet. Space Sci. 12, 1169 (1964). 2. F. C. FEHSENFELD, A. L. SCHMELTEKOPF and E. E. FERGUSON, Planet. Space Sci. 13,219 (1965). 3. F. C. FEHSENFELD, P. D. GOLDAN, A. L. SCHMELTEKOPF and E. E. FERGUSON, PIanet. Space Sci. 13, 579. 4. F. C. FEHSENFELD, A. L. SCHMELTEKOPF, H. I. SCHIFFand E. E. FERGUSON, to be published. 5. A. L. SCHMELTEKOPF, P. D. GOLDAN,F. C. FEHSENFELD and E. E. FERGUSON, to be published. 6. L. F. PHILLIPSand fi. I. SCHIFF,J. Chem. Phys. 36, 1509 (1962). 7. J. W. LINNE~ and D. G. H. MARSDEN.Proc. Rov. Sot.. Load. A234.489 (1956). , . I ’ 8. E. LINDHOLM,Rev. Sci. Instrum. 31,21b (1960). ’ 9. D. R. BATESand M. NICOLET,J. Atmos. Terr. Phys. 18, 65 (1960). 1Oa. F. R. GILMORE,Memorandum RM-4034-PR, The Rand Corp., Santa Monica, California, June 1964. lob. F. R. GILMORE,J. Quant. Spect. Rad. Transfer 5,369 (1965). 11. A. DALGARNOand j. C. G.-WALKER, J. Atmos. Sci. Zi, 46j (1964). 12. R. B. NORTON.T. E. VAN ZANDTand J. S. DENISON.Proceedinps on the ” of J the International Conference J
13. 14. 15. 16. 17. 18.
Zonosphere, p.26. London (1963). H. E. HINTEREGGER, L. A. HALL and G. SCHMLDTKE, Space Research V. North Holland, Amsterdam. A. 0. NIER, J. H. HOFFMAN,C. Y. JOHNSONand J. C. HOLMES,J. Geophys. Res. 69,979 (1964). J. C. HOLMES,C. Y. JOHNSONand J. M. YOUNG, Space Research V. North Holland, Amsterdam. T. M. DONAHUE,Planet. Space Sci., in press. E. C. ZIPF and W. G. FASTIE,J. Geophys. Res. 69,2357 (1964). E. C. ZIPF, J. Geomagn. Geoelect., in press. H3ME!PeHHRM, H03+$lBQHeHT CKOPOCTIl AJIH peaK9ZfH N,+ + 0 ---, NO+ +N, Ha 300°K, oKaaaacH kla = 2.5( fl) x 10-lo~~* ceK-I. CooBnIeHni o KaKnxnnGo npemnllx na60paTopHbrx H3MepemGI 3~oP peaHqHH np~ TepMn4ecKHx aHeprMsx, ~0 c~lx IlOp He llOCTyllHJlO. 3Ta pEiK~I0-I HeCOMHt?HHO EiI’paCT BaxHyIO POJIb B CJIOIIX EIOHOC@PbI i?i? mF 1, FIBJE=IRCb OTBeTCTBeHHOti 38 3HEFIHTeJlbHJ’IO nOTepI Na+ Ii 33 IIt?peB&?lIIHBaHHe CKOPOCTZi IIOTepn Nz+ MOllf%yJr~pHblM K~CJlOpO~OM.
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