The production of electronically-excited species from the photolysis of N2H4and N2D4at 193 nm

Lindberg, Pia; Raybone, D.; Salthouse, J. A.; Watkinson, T.M.; Whitehead, J. Christopher

doi:10.1080/00268978700102981

Cited by 22 publications

(4 citation statements)

References 19 publications

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“…In order to place precise upper limits for the H atom primary quantum yields in alkylated diamine photolysis, it is necessary to experimentally verify the primary yield of NH 2 or other radicals, if any. (Direct NH 2 formation in N 2 H 4 photolysis has previously been suggested, [13][14][15] whose yield though not measured must be small since we have shown H atoms to be the principal product in the photolysis. 1 ) Also, the determination of photofragment angular and fragment translational energy disposal using time-of-flight methods would be very useful in obtaining details of the dynamics of the photodissociation which occurs over the excited electronic potential energy surface(s).…”

Section: Discussionmentioning

confidence: 61%

Section: Discussionmentioning

confidence: 67%

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UV Absorption Cross Sections, Laser Photodissociation Product Quantum Yields, and Reactions of H Atoms with Methylhydrazines at 298 K

Vaghjiani

1997

J. Phys. Chem. A

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The gas-phase photochemistry of the diamines monomethylhydrazine (CH 3 NHNH 2 ) and unsymmetrical dimethylhydrazine ((CH 3 ) 2 NNH 2 ) has been studied in the ultraviolet (UV) at 298 K. Relative UV absorbance spectra of dilute mixtures of the diamine in He buffer gas were recorded in the region 140-310 nm with an instrument resolution of 0.25 nm. These were converted to absolute absorption cross section profiles by scaling the data with absolute 253.65-nm cross section values of σ 253.65 ) (8.022 ( 0.481) × 10 -20 and (35.883 ( 2.152) × 10 -20 cm 2 molecule -1 for CH 3 NHNH 2 and (CH 3 ) 2 NNH 2 , respectively, which we also determined in this work. Both compounds exhibit continuous diffuse absorption bands in the UV that correspond to electronic transitions to dissociative singlet excited states. Laser photodissociation product measurements revealed the absolute H atom primary quantum yields to be Φ 248 ) 1.07 ( 0.02, Φ 222 ) 0.99 ( 0.01, and Φ 193 ) 0.94 ( 0.07 for CH 3 NHNH 2 photolysis at 248, 222, and 193 nm, respectively. The corresponding values for (CH 3 ) 2 NNH 2 photolysis were Φ 248 ) 0.97 ( 0.06, Φ 222 ) 0.91 ( 0.06, and Φ 193 ) 0.90 ( 0.04. Kinetic measurements gave the absolute second-order H atom rate coefficients to be k ) (7.60 ( 1.14) × 10 -13 and (13.48 ( 2.02) × 10 -13 cm 3 molecule -1 s -1 respectively for reactions with CH 3 NHNH 2 and (CH 3 ) 2 NNH 2 at 298 K and in 26.0 Torr of He. Trends in the UV absorption cross section profiles, photodissociation product distributions, and the H atom reactivities in the homologous diamine series (CH 3 ) 2 NNH 2 , CH 3 NHNH 2 , and N 2 H 4 are discussed.

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Section: Discussionmentioning

confidence: 61%

Section: Discussionmentioning

confidence: 67%

UV Absorption Cross Sections, Laser Photodissociation Product Quantum Yields, and Reactions of H Atoms with Methylhydrazines at 298 K

Vaghjiani

1997

J. Phys. Chem. A

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“…293 nm [191. The absolute quantum yield for the reaction in which the weaker 1121 N-N bond is cleaved was not reported, though it was concluded that the quantum yield for the visible emission was small of the order of a few percent at the most. Other studies have also reported formation of the excited state imidogen radical (NH(A)) in hydrazine photolysis [14,17,201. This can be explained to be due to secondary photolysis of the primary photofragments and not as a result of direct N2H4 dissociation.…”

Section: Introductionmentioning

confidence: 90%

Laser photolysis studies of hydrazine vapor: 193 and 222‐nm H‐atom primary quantum yields at 296 K, and the kinetics of H + N₂H₄ reaction over the temperature range 222–657 K

Vaghjiani

1995

Int J of Chemical Kinetics

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The primary quantum yield of H-atom production in the pulsed-laser photolysis of hydrazine vapor, N2H4 + h v + H + NzH3, was measured to be (1.01 2 0.12) at 193 nm relative to HBr photolysis, and (1.06 2 0.16) at 222 nm relative to 248-nm NzH4 photolysis, in excess He buffer gas a t 296 K. The H-atoms were directly monitored in the photolysis by cw-resonance fluorescence detection of H('S) at 121.6 nm.The high H-atom yield observed in the photolysis is consistent with the continuous ultraviolet absorption spectrum of NzH4 involving unit dissociation of the diamine from repulsive excited singlet state(s). The laser photodissociation of N2H4 was thus used as a 'clean' source of H-atoms in excess NzH4 and He buffer gas to study the gas-phase reaction, H + NzH4 -products; (kl), in a thermostated photolysis reactor made of quartz or Pyrex. The pseudo-first-order temporal profiles of [HI decay immediately after photolysis were determined for a range of different hydrazine concentrations employed in the experiments to calculate the absolute second-order reaction rate coefficient, k l . The Arrhenius expression was determined to be k l = (11.7 -t 0.7) X exp[-(1260 2 20)/T] cm3 molec-l s-l in the temperature range 222-657 K.The rate coefficient a t room temperature was, within experimental errors, independent of the He buffer gas pressure in the range 24.5-603 torr. The above temperature dependence of k1 is in excellent agreement to that we determine in our discharge flow-tube apparatus in the temperature range 372-252 K and in 9.5 torr of He pressure. The Arrhenius parameters we report are consistent with a metathesis reaction mechanism involving the abstraction of hydrogen from NzH4 by the H-atom.

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“…The parent compound, hydrazine (H 2 NNH 2 ), is kinetically stable, but thermodynamically unstable . It is one of the simplest nitrogen compounds and an important rocket fuel; thus it has been well characterized experimentally − and theoretically. − …”

Section: Introductionmentioning

confidence: 99%

Dipole-Bound Anion of the HNNH₃ Isomer of Hydrazine. An Ab Initio Study

1999

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The possibility of electron binding to the HNNH 3 and H 2 NNH 2 tautomers of hydrazine was studied at the coupled cluster level of theory with single, double, and noniterative triple excitations. The HNNH 3 tautomer, with a dipole moment of 5.4 D, binds an electron by 1076 cm -1 whereas the H 2 NNH 2 tautomer forms neither a dipole-nor valence-bound anionic state. It is suggested that the HNNH 3 tautomer, which is kinetically stable but thermodynamically unstable relative to H 2 NNH 2 , may be formed by photodetachment from the N 2 H 4 -species examined in this work.

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The production of electronically-excited species from the photolysis of N₂H₄and N₂D₄at 193 nm

Cited by 22 publications

References 19 publications

UV Absorption Cross Sections, Laser Photodissociation Product Quantum Yields, and Reactions of H Atoms with Methylhydrazines at 298 K

UV Absorption Cross Sections, Laser Photodissociation Product Quantum Yields, and Reactions of H Atoms with Methylhydrazines at 298 K

Laser photolysis studies of hydrazine vapor: 193 and 222‐nm H‐atom primary quantum yields at 296 K, and the kinetics of H + N₂H₄ reaction over the temperature range 222–657 K

Dipole-Bound Anion of the HNNH₃ Isomer of Hydrazine. An Ab Initio Study

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The production of electronically-excited species from the photolysis of N2H4and N2D4at 193 nm

Cited by 22 publications

References 19 publications

UV Absorption Cross Sections, Laser Photodissociation Product Quantum Yields, and Reactions of H Atoms with Methylhydrazines at 298 K

UV Absorption Cross Sections, Laser Photodissociation Product Quantum Yields, and Reactions of H Atoms with Methylhydrazines at 298 K

Laser photolysis studies of hydrazine vapor: 193 and 222‐nm H‐atom primary quantum yields at 296 K, and the kinetics of H + N2H4 reaction over the temperature range 222–657 K

Dipole-Bound Anion of the HNNH3 Isomer of Hydrazine. An Ab Initio Study

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The production of electronically-excited species from the photolysis of N₂H₄and N₂D₄at 193 nm

Laser photolysis studies of hydrazine vapor: 193 and 222‐nm H‐atom primary quantum yields at 296 K, and the kinetics of H + N₂H₄ reaction over the temperature range 222–657 K

Dipole-Bound Anion of the HNNH₃ Isomer of Hydrazine. An Ab Initio Study