Photolysis Of Ammonia Research Articles

Vacuum UV photolysis of NH 3: rotational distribution of NH(c 1Π) and the heat of formation of NH

The rotationally resolved emission spectra of NH(c 1Π) was observed in the vacuum UV photolysis of ammonia by Ar, Kr and H resonance lines. Hot rotational distribution was reconfirmed for photolysis by either the Kr or the H line, while, in the case of Ar, NH(c 1Π) was found to be cold. From the maximum rotational line observed in the 123.6 nm photolysis, the heat of formation of NH is determined to be 90.2–91.3 kcal/mol.

An electron spin resonance study of the photolysis of azide ions in liquid ammonia: formation of imine radical anions in the presence of alkenes

U.v. photolysis of ammonia or ammonia-ethereal solutions containing sodium or tetra-n-butylammonium azide leads to the formation of the diazene radical anion [HNNH]–˙, which is detectable by e.s.r. spectroscopy. The e.s.r. spectrum of the ammonia-solvated electron is also observed and the primary photochemical process is probably ejection of an electron from N3– to give the azido radical N3˙. Addition of N3˙ to ammonia and subsequent loss of nitrogen accompanied or followed by a hydrogen shift would give the hydrazyl radical, deprotonation of which gives [HNNH]–˙. In the presence of mono- or 1,1-di-alkylated ethenes, R1R2CCH2, the spectrum of [HNNH]–˙ is replaced by one assigned to the imine radical anion [R1R2CH–C(H)NH]–˙ possible routes for formation of such species following addition of N3˙ to the alkene are discussed.

Efficient recovery of intermediate hydrazine in gas-phase photolysis of ammonia by absorption into falling film of aqueous ammonia.

Efficient recovery of intermediate hydrazine in gas-phase photolysis of ammonia by absorption into falling film of aqueous ammonia.

Argon fluoride (ArF) excimer laser photolysis of ammonia. Formation of imidogen and imidogen-d in the A3.PI. state

NH/sub 3/ and ND/sub 3/ were photolyzed with an ArF (193 nm) excimer laser. Besides weak emission from ND(b/sup 1/..sigma../sup +/), strong fluorescence emission from NH(A/sup 3/PI) were observed in the investigated wavelength region 130-500 nm. Measurements of the fluorescence intensity and rotationally resolved spectra indicate a two-photon resonance process. In this dissociation process rotationally hot NH (ND) in the A/sup 3/PI state is generated with almost no translational energy left for either detached H atom. The dynamics of the photodissociation is discussed. Lifetime measurements of the excited A/sup 3/PI states indicate (a) a slight isotope effect and (b) longer zero-pressure lifetimes than previously recommended.

The reaction NH2 + PH3 → NH3 + PH2: Absolute rate constant measurement and implication for NH3 and PH3 photochemistry in the atmosphere of Jupiter

It has been suggested that the photochemistries of NH3 and PH3 are linked in the upper atmosphere of Jupiter. Specifically, the reaction NH2 + PH3 → NH3 + PH2 would, if the rate were fast enough at Jovian stratospheric temperatures, regenerate ammonia in the upper atmosphere while at the same time accelerating the decomposition of phosphine. The absolute rate constant for this reaction has been measured over the temperature interval 218–456 K using the technique of flash photolysis‐laser‐induced fluorescence (FP‐LIF). NH2 radicals were produced by flash photolysis of ammonia highly diluted in argon, and the decay of fluorescent NH2 photons was measured by multiscaling techniques. At each of the five temperatures employed in the study the results were shown to be independent of variations in [PH3], total pressure (Argon), and flash intensity (i.e., initial [NH2]). The rate constant results are best represented for 218 ≤ T ≤ 456 K by the expression k = (1.52 ± 0.16) × 10−12 exp (−928 ± 56/T) cm3 molecules−1 s−1, where the error quoted is 1 standard deviation. This represents the first determination of the rate constant for the reaction NH2 + PH3. The data are compared with an estimate made in order to account for results of the radiolysis of NH3‐PH3 mixtures. The Arrhenius parameters determined here for NH2 + PH3 are contrasted with those for the corresponding reactions of η and OH with PH3. The results are also discussed theoretically and the implications considered for models of the photochemistry of the atmosphere of Jupiter. Since we now find that the rate constant for the reaction NH2 + PH3 → NH3 + PH2 is 2 orders of magnitude shower than required in the model, it appears that this reaction can make only a negligible contribution to both the recycling of NH3 and the decomposition of PH3 in the upper atmosphere of Jupiter.

Formation and photochemistry of Methylamine in Jupiter's atmosphere

The formation of methylamine (CH 3NH 2) in the upper troposphere and lower stratosphere of Jupiter is investigated. Translationally hot hydrogen atoms are produced in the photolysis of ammonia, phosphine, and acetylene which react with methane to produce methyl (CH 3) radicals; the latter recombine with NH 2 to form CH 3NH 2. Also, methane is catalytically dissociated to CH 3 + H by the species C 2 and C 2H produced in the photolysis of acetylene. It is shown that the combined production of CH 3NH 2 and subsequent photolysis to HCN is unlikely to account for the HCN observed near Jupiter's tropopause. Recombination of NH 2 and C 2H 5N followed by photolysis to HCN is the preferred path. Production of C 2H 6 by these two processes is negligible in comparison to the downward flux of C 2H 6 from the Lyman α photolysis region of CH 4. An upper limit column density on CH 3PH 2 is estimated to be ∼10 13 cm −2 as compared to 10 15 cm −2 for CH 3NH 2. Hot H atoms account for a negligible fraction of the total ortho-para conversion by the reaction H + H 2

HCN formation on Jupiter: The coupled photochemistry of ammonia and acetylene

A model is presented for the formation of HCN in the upper troposphere and lower stratosphere of Jupiter by ultraviolet photolysis of the C 2H 5N isomer aziridine, a product of the recombination of NH 2 and C 2H 3 radicals, which originate, respectively, from ammonia photolysis and addition of H atoms to acetylene. An HCN column density of ∼ 2 × 10 17 cm −2 in the tropopause region, which is comparable to that observed by A. T. Tokunaga, S. C. Beck, T. R. Geballe, J. H. Lacy, and E. Serabyn ( Icarus 48, 283–289, 1981), is predicted when vertical mixing is slow above the ammonia cloudtops. Sensitivity of the HCN column density to the individual rate constants and the eddy diffusion coefficient profile is discussed, as is the possibility of the existence of additional HCN-yielding pathways. Ammonia, which is saturated in the upper troposphere, is strongly depleted by photolysis in the lower stratosphere. Phosphine is also strongly depleted by photolysis and its abundance in the upper troposphere is shown to depend strongly on vertical mixing in the tropopause region. The possibility of the formation of phosphirane, the P-containing analog of aziridine, is considered but found to be substantially less probable than aziridine.

Formation of hydrazine by photolysis of ammonia in a flow system.

Formation of hydrazine by photolysis of ammonia in a flow system.

Rate constant for the reaction NH2+ NO from 216 to 480 K

The absolute rate constant for the reaction NH2+ NO → products, has been measured at five temperatures from 216 to 480 K by the technique of combined flash-photolysis and laser-induced fluorescence (FP–LIF). NH2 radicals were produced by the flash photolysis of ammonia and the fluorescent NH2 photons were measured by multiscaling techniques. At each temperature the results were independent of variations in [NO], total pressure and flash intensity (i.e. initial [NH2]). The results are best represented by the expression k=(2.77 ± 0.89)× 10–7T–1.67 ± 0.05 cm3 molecule–1 s–1, where the error quoted is one standard deviation. The results are compared with previous determinations using the techniques of mass spectrometry, absorption spectroscopy, laser absorption spectroscopy and laser-induced fluorescence. The implications of the results are discussed with regard to combustion, post combustion and atmospheric chemistry. The results are also discussed theoretically.

Flash photolysis of ammonia in the presence of oxygen

Flash photolysis of ammonia in the presence of oxygen was studied using the intracavity laser spectroscopy technique. The reaction NH 2 + O 2 was demonstrated to be of no importance and a value of k 6 < 1.5 × 10 −17 cm 3/molecule s was estimate Accelerating NH 2 decay with oxygen addition is due to the reaction NH 2 + HO 2 and its rate constant was found to be k 7 = 2.5 × 10 −11 cm 3/molecules.

Ammonia photolysis and the greenhouse effect in the primordial atmosphere of the earth

Photochemical calculations indicate that in the prebiotic atmosphere of the Earth ammonia would have been irreversibly converted to N 2 in less than 40 years if the ammonia surface mixing ratio were ≤ 10 −4. However, if a continuous outgassing of ammonia were maintained, radiative equilibrium calculations indicate that a surface mixing ratio of ammonia of 10 −5 or greater would provide a sufficient greenhouse effect to keep the surface temperature above freezing. With a 10 −4 mixing ratio of ammonia, 60 to 70% of the present day solar luminosity would be adequate to maintain surface temperatures above freezing. A lower limit to the time constant for accumulation of an amount of nitrogen equivalent to the present day value is 10 my if the outgassing were such as to provide a continuous surface mixing ratio of ammonia ≥ 10 −5.

Enrichment of nitrogen-15 by the direct laser photolysis of ammonia-d3 in the transition

Ammonia-d3 of differing 14N/15N ratios has been photolysed in the [Formula: see text] transition using a narrow-band-width, frequency-doubled, pulsed dye laser. At specific excitation wavelengths, chosen by absorption spectroscopy, the product nitrogen is enriched in 15N, a maximum enrichment factor of 4.8 being attained. The initial isotopic selectivity of excitation is largely retained in the nitrogen product, even though the primary photodissociation forms free radicals and N2 is formed only after a sequence of secondary reactions. Quantum yields of nitrogen and hydrogen formation have been measured at very low conversions as a function of the time of irradiation. The initial yield of nitrogen appears to be zero and that of hydrogen 0.25.

Analysis of NH Spectrum

The A3Π – X3Σ− transition of NH is a common feature of cometary spectra. Since the NH molecule is likely to be formed by photodissociation of molecules such as ammonia or hydrazine, identifying the final states of the photolysis would shed light on the identity of the parent. Stief and DeCarlo noted that the photolysis of ammonia at 123.6 nm results in emission at 324.0 nm in the c1Π – a1Δ system. They suggested that in the absence of collisions in the coma, the NH(a1Δ) should accumulate if ammonia is the source of NH radicals. The absence of the singlet system in this view would suggest another parent molecule than ammonia as the source of the NH radical. However, the pumping rate of the UV transitions in a comet is also very small. This note will show that the transition rate for the a1Δ – X3Σ− transition is sufficiently fast to deplete any a1Δ concentration formed in the original photolysis process.

Quenching and radiative lifetimes for NH(b 1Σ +, υ′ = 0)

Electronically excited NH(b 1Σ +, υ′ = 0) has been produced in the vacuum ultraviolet photolysis of ammonia at pressures in the millitorr range. Absolute rate coefficients for quenching and radiation have been determined by time-resolved measurements of the emission near 471 nm of the 0,0 band of the NH(b 1Σ +−X 3Σ −) system. A radiative lifetime of 17.8 −3.0 +4.7 ms is reported and rate coefficients are reported for quenching by Ar, NH 3, CH 4, CO and O 2. None of these collision partners leads to rapid quenching.

ChemInform Abstract: NH2 RADICALS TRAPPED ON THE SURFACE OF POROUS VYCOR GLASS AT 77 K

AbstractDie Ergebnisse der ESR‐Untersuchungen von durch Photolyse von NH3 erzeugten und an porösen Vicorglasoberflächen bei 77 K adsorbierten NH2‐ Radikalen werden behandelt.

Light emission of the photofragments produced by photolysis of ammonia and ammonia- d3 at 147, 123.6 and 104.8 nm: first observation of the b 1Σ + → X 3Σ − transition of NH and ND

Excited photofragments are produced by vacuum ultra-violet photolysis of gaseous ammonia and ammonia- d 3. The following transitions have been recorded: NH 2(ND 2) A 2A 1 → X 2B 1 by irradiation with xenon and krypton resonance lamps; NH (ND) c 1π → a 1Δ and b 1Σ + → X 3 Σ − with the krypton and argon resonance lamps. This last emission, observed here for the first time, occurs at 471 nm and it leads to the singlet—triplet splitting a 1Δ — X 3Σ − of NH, with an energy of 1.561 eV (1.565 eV for ND). The rotational temperatures of the c and b excited states of NH and ND radicals have been measured and the primary processes leading to the excited photofragments are discussed.

NH2 Radicals Trapped on the Surface of Porous Vycor Glass at 77 K

Abstract The results of ESR studies of the amino radicals produced by the photolysis of ammonia adsorbed on the surface of porous Vycor glass at 77 K are described. The observed ESR signal patterns of the amino radicals were remarkably affected by the amount of ammonia on the surface. The isotropic and anisotropic spectra were analyzed by the use of isotopically-substituted amino radicals.

Transition metal eight-coordination—V: The liquid ammonia photolysis of ammonium octacyanomolybdate(IV)

Two observable photolytic intermediates are formed in the liquid ammonia photolysis of (NH 4) 4[Mo(CN) 8], in contrast to the photoaquation reaction where only one intermediate can be observed, even though four cyano ligands are displaced in the photolysis. A partially deammonated product (Mo(CN) 4(NH 3) 2 has been isolated from the reaction on a synthetic scale and characterized spectrally and magnetically. Preliminary results with octacyanotungstate(IV) are also noted.

Emission of imino radicals in the c1.pi. state formed from the photolysis of ammonia, methylamine, and ethylenimine at 123.6 nm

Emission of imino radicals in the c1.pi. state formed from the photolysis of ammonia, methylamine, and ethylenimine at 123.6 nm

Light emission of the photofragments produced by photolysis of ammonia and ammonia- d3 at 147, 123.6 and 104.8 nm: : First observation of the b 1Σ + → X 3Σ − transition of NH and ND

Excited photofragments are produced by vacuum ultra-violet photolysis of gaseous ammonia and ammonia- d 3. The following transitions have been recorded: NH 2(ND 2) Ã 2A 1 → X̃ 2B 1 by irradiation with xenon and krypton resonance lamps; NH (ND) c 1π → a 1Δ and b 1Σ + → X 3 Σ − with the krypton and argon resonance lamps. This last emission, observed here for the first time, occurs at 471 nm and it leads to the singlet—triplet splitting a 1Δ − X 3Σ − of NH, with an energy of 1.561 eV (1.565 eV for ND). The rotational temperatures of the c and b excited states of NH and ND radicals have been measured and the primary processes leading to the excited photofragments are discussed.