Photolysis Of Ammonia Research Articles

Emission spectra of atomic and molecular nitrogen from photolysis of ammonia in solid neon

Dilute samples of NH3 and ND3 in solid neon near 4 K were irradiated at 200 or 173 or 143 nm with light from a synchrotron. We recorded emission spectra of atomic N, involving states 4So, 2Po and 2Do, and of molecular N2, involving states X 1Σg+, A 3Σu+, B 3Πg and C 3Πu in systems with vibrational progressions in the lower states. The emission spectra covered the near-ultraviolet, visible and near-infrared regions from 200 to 1100 nm; the far-ultraviolet absorption spectrum for the precursor NH3 in solid neon was also measured. Recorded for samples in darkness after irradiation at 143 nm during warming from ∼5 K to ∼8 K, thermoluminescent spectra consisted mostly of lines emitted by molecular N2. The analysis of these spectra, and their temporal development, provides information about the nature of dissociative and trapping processes in solid neon under cryogenic conditions involving monochromatic synchrotron radiation.

Formation and characterization of VUV photolytically-induced (NH2)(NH3)n aggregates, 0 ≤ n ≤ 3

The formation of amidogen radical may be an important precursor toward the formation of prebiotic molecules on the surface of ice grains in interstellar clouds. Many laboratory experiments aimed at characterizing the photolysis of ammonia. Wide shifts were observed between the solid phase and the gas phase experiments, suggesting the presence of aggregates in solid phase experiments. We attempt to characterize the formation of aggregates between amidogen radical and ammonia during the VUV irradiation of ammonia. To this end Fourier transform infrared (FTIR) spectroscopy was used in combination with the matrix isolation technique in order to characterize species formed during the photolysis of ammonia. The experimental IR spectra were compared with the theoretical frequencies obtained from post Hartree–Fock and DFT calculations for the amidogen radical and its complexes with ammonia molecules. Experimentally, the matrix isolation technique allow us to observe several bands due to the formation of (NH2)(NH3)n complexes. These bands are assigned thanks to the theoretical calculations.

The role of photochemical processes in evolution of the isotopic composition of the atmosphere of Titan

Molecular nitrogen, the main component of the modern atmosphere of Titan, may have formed without significant changes in the nitrogen and hydrogen isotopic composition from the clathrate hydrate of ammonia NH3 · H2OSLD, which is the main accreted form of nitrogen. The most preferable transformation mechanism of NH3 · H2OSLD into atmospheric N2 is its thermal decomposition in the interior of Titan rather than the photochemical decomposition of ammonia in the upper atmosphere of early Titan. The photolysis of ammonia does not lead to a change in the isotopic composition of nitrogen, as all the nitrogen remains in Titan’s atmosphere. The photolysis of NH does not lead to a change in the isotopic composition of nitrogen in Titan’s atmosphere. Fractionation of hydrogen and nitrogen isotopes during the impacts of comets with Titan does not seem to be significant either. It will be possible to determine the dissociative fractionation factor, the original ratio 14N/15N, and the mass of Titan’s original atmosphere when fractionation of nitrogen isotopes in Titan’s atmosphere is examined in additional theoretical and experimental studies that take into account processes occurring during the formation of a system of Saturn’s satellites.

Real-Time Observation of Formation and Relaxation Dynamics of NH4 in (CH3OH)m(NH3)n Clusters

The formation and relaxation dynamics of NH4(CH3OH)m(NH3)n clusters produced by photolysis of ammonia-methanol mixed clusters has been observed by a time-resolved pump-probe method with femtosecond pulse lasers. From the detailed analysis of the time evolutions of the protonated cluster ions, NH4(+)(CH3OH)m(NH3)n, the kinetic model has been constructed, which consists of sequential three-step reaction: ultrafast hydrogen-atom transfer producing the radical pair (NH4-NH2)*, the relaxation process of radical-pair clusters, and dissociation of the solvated NH4 clusters. The initial hydrogen transfer hardly occurs between ammonia and methanol, implying the unfavorable formation of radical pair, (CH3OH2-NH2)*. The remarkable dependence of the time constants in each step on the number and composition of solvents has been explained by the following factors: hydrogen delocalization within the clusters, the internal conversion of the excited-state radical pair, and the stabilization of NH4 by solvation. The dependence of the time profiles on the probe wavelength is attributed to the different ionization efficiency of the NH4(CH3OH)m(NH3)n clusters.

Solvation structure and stability of hypervalent NH 4(CH 3OH) m(NH 3) n clusters

Ionization potentials (IPs) of NH 4(CH 3OH) m (NH 3) n radicals produced by an ArF excimer laser photolysis of ammonia–methanol mixed clusters are determined by the photoionization threshold measurements. The observed IPs show the different evolutions with increasing the number of ammonia and methanol solvents. The IPs are also examined by ab initio calculations, which suggest that the hydrogen bond network is dominant in the case of adding methanol. Moreover, the lack of NH 4 ( CH 3 OH ) m + ( m ⩾ 1) signals indicates that they have very short lifetimes (<4 ns) due to a fast elimination of hydrogen-atom from NH 4 radical via tunneling.

Product Studies of Inelastic and Reactive Collisions of NH2 + NO: Effects of Vibrationally and Electronically Excited NH2†

The reaction between NH 2 and NO has been studied by time-resolved step-scan Fourier transform infrared emission spectroscopy. We observe time-dependent emission from vibrationally excited NO, N 2 O, and H 2 O arising from the interaction of NO with both relaxed and initially vibrationally and electronically excited NH 2 , produced by the 193 nm laser photolysis of ammonia. The excited NH 2 gives rise to a rapidly decaying emission signal. The correlated time dependences of the vibrationally excited NO and N 2 O signals suggest that they are formed by direct collisions of NO with the vibrationally excited NH 2 . There is sufficient excitation of the NH 2 to overcome the high barrier to N 2 O formation. The emission from vibrationally excited H 2 O shows that its formation is delayed, with a significant induction period. The time dependence of the H 2 O induction period matches well to the decay of emissions from the v 1 and v 3 bands of NH 2 , suggesting that the NH 2 is deactivated to its ground electronic and vibrational states before the water product is produced by reaction with NO.

Partial pressures and nature of products. Application to the photolysis of PH3 and NH3 in the atmosphere of Jupiter and Saturn.

The photolysis of mixtures of gases containing NH3 or PH3 presents important differences mainly due to the strength of the X-H bond. On some examples, these differences are evidenced and the consequences for mixtures of gases containing these two compounds are shown: the photolysis of ammonia and ethylene mainly gives ethyl-, butyl- and hexylamine whereas the photolysis of phosphine and ethylene leads to ethyl- and vinylphosphine. When gaseous mixtures of NH3, PH3 and ethylene are photolyzed together, the presence of phosphine dramatically decreases the formation of nitrogen derivatives. The relevance of such lab studies to the atmospheres of Jupiter and Saturn is discussed.

Flame Front Observation of Ammonia Decomposition and Oxidation Using 193 nm Two-Photon Photolysis and Photofragment Fluorescence

The 193 nm output of an ArF laser is utilized in the detection of gas-phase ammonia in methane–air flames of varying stoichiometry. Photolysis of ammonia with the 193 nm radiation results in NH photofragment fluorescence—the intensity of which is found to be proportional to the concentration of the ammonia present. Detection limits of &lt;1 ppm of gas-phase ammonia are readily achievable under atmospheric flame conditions. Two-dimensional images of ammonia decomposition have been obtained for a laminar premixed flame, clearly revealing the conical reaction zone. Thermal decomposition of the ammonia is observed in the pre-flame zone of the burner in addition to its oxidation in the reaction zone.

Near ultraviolet photolysis of ammonia and methylamine studied by H Rydberg atom photofragment translational spectroscopy

H(D) Rydberg atom photofragment translational spectroscopy has been used to provide new insights into the primary photochemistry of methylamine, ammonia and various of their respective isotopomers following excitation at wavelengths in the near ultraviolet (UV). The bimodal appearance of the total kinetic energy release (TKER) spectra associated with H atom production in the near UV photolysis of methylamine is consistent with there being both ‘dynamical’ (high TKER) and ‘statistical’ (slower) contributions to the total H + CH3NH dissociation yield. Both contributions arise as a result of one H atom tunnelling through (or passing over) an earlier barrier in the N{H dissociation coordinate of the ~ A state potential energy surface and then evolving into the region of the conical intersection connecting the ~ A state and ground-state surfaces. ‘Dynamical’ energy disposal is associated with those molecules which pass directly through this conical intersection en route to the ground-state (H + CH3NH( ~ X)) asymptote, whilst the ‘statistical’ contribution is attributed to those molecules that ‘miss’ the conical intersection on the rst traversal and only make the ~ A! ~ X transfer on a later encounter. This interpretation has inspired further consideration of the form of the TKER spectra derived from TOF measurements of the H/D atom products arising in the dissociation of various isotopomers of ammonia following excitation to the 0 0 and 2 1 levels of their respective ~ A states. A similar model which associates ‘dynamical’ energy disposal with those molecules that pass through the ~ A= ~ X conical intersection during bond extension, and ‘statistical’ kinetic energy release with those that transfer during N{H(D) bond compression, appears to provide a qualitative explanation for the way the observed H and/or D atom yields and their associated TKER spectra vary with excitation wavelength (0 0 versus 2 1 band excitation) and isotopic composition.

A quantum chemical investigation of possible intermediates in the reaction of the amidogen and hydroperoxyl radicals

The reaction NH2+HO2→products, a reaction of atmospheric interest, has been studied using ab initio molecular orbital calculations with extended basis sets [6-311++G** and 6-311++G(2df,2pd)], and a variety of methods accounting for electron correlation such as second order Mo/ller–Plesset perturbation theory (MP2) with all electrons, quadratic configuration interaction singles and doubles with triples correction [QCISD(T)], complete active space [CAS(8,8)], and multireference double excitation configuration interaction (MRDCI). Also, the performance of density functional (DFT) calculations has been investigated. In the present study, all stationary points on various potential energy surfaces giving rise to different products, HNO+H2O, NH2O+OH, NH3+O2, H2O2+NH, and HNOO+H2, have been optimized and characterized by their Hessian matrix. Amine oxide and dihydroxyamine have been found to be the precursors for HNO formation. In addition, the paper attempts to explain the experimental finding, nonobservation of OH⋅ during photolysis of ammonia, and it demands new experiments with spectroscopic identification of OH radicals.

New vibronic states of NH 2 observed in ammonia photolysis

We report the observation of two high energy vibronic transitions in the NH 2 radical, unreported so far. The NH 2 radical was produced in a laser photolysis experiment and expanded in a molecular beam machine. Laser excitation and dispersed fluorescence spectra provided term values and rotational constants in good agreement with theoretical predictions.

Determination of the internal state distribution of NO(X 2Π) produced in the O(3P)+NH(X 3Σ−) reaction

The internal state distribution of the NO product from the O(3P)+NH(X 3Σ−) reaction has been determined from a laser fluorescence experiment in a cell at a total pressure of 60 mTorr. The O atom and the NH reagents were prepared in a microwave discharge in oxygen and by the two-photon 193 nm photolysis of ammonia, respectively. The NO product was observed in the vibrational levels v=1–8 by laser fluorescence excitation in A 2Σ+–X 2Π bands. The nascent vibrational state distribution was found to be monotonically decreasing vs increasing v. The v=1 rotational state distribution, extrapolated back to zero photolysis-probe delay, could be parametrized as a 1130±50 K Boltzmann distribution. Very little of the available energy is found as internal excitation of the NO product. The O+NH→H+NO reaction is expected to proceed by the formation and decay of a short-lived HNO complex. The observed NO vibrational state distribution is interpreted in terms of a Franck–Condon model involving the overlap of vibrational wave functions for the NO stretch coordinate in the HNO complex with those for vibration in the free NO product. The NO rotational state distribution is governed largely by kinematic constraints in this H+HL→HH+L reaction, where H and L are heavy and light atoms, respectively.

Photolysis of ammonia in the presence of acetylene. A plausible explanation for the formation of HCN and chromophores on Jupiter

Photolysis of ammonia in the presence of acetylene. A plausible explanation for the formation of HCN and chromophores on Jupiter

Gas Phase Reactions Relevant to Chemical Vapor Deposition: Optical Diagnostics

AbstractLaser photolysis, optical emission, and laser-induced fluorescence (LIF) were used to investigate laser driven decomposition processes in the gas phase pertaining to the systems: SiH4 → Si (s) and SiH4 → NH3 → Si3N4 (s). These processes are important to silicon/ silicon-nitride chemical vapor deposition, flame-driven gas phase silicon-particle nucleation, and laser-induced processes for materials fabrication. UV laser photolysis was used to generate SiHx and NHx species from silane and ammonia. A number of photofragments were identified by emission from excited states. The rate of reaction of NH2 with silane was measured using LIF to detect NH2 as a function of time following photolysis of ammonia

ChemInform Abstract: Formation of HCN and Acetylene Oligomers by Photolysis of Ammonia in the Presence of Acetylene: Applications to the Atmospheric Chemistry of Jupiter.

AbstractAt room temp., UV photolysis (185 nm; at 206 nm much lower yield) of NH3 in the presence of acetylene (maximum yield at ca. 8:1) leads to HCN and brown oligomers of acetylene, thus providing a plausible solution to two previously intractable problems concerning the atmospheric chemistry of Jupiter.

Formation of hydrogen cyanide and acetylene oligomers by photolysis of ammonia in the presence of acetylene: applications to the atmospheric chemistry of Jupiter

HCN is formed by the photolysis of ammonia in the presence of acetylene at room temperature. There is a 70% decrease in the yield of HCN when the temperature is lowered to 178 K and two new reaction products, acetonitrile and acetaldehyde ethylidenehydrazone (6), are formed. Photolysis of 6 yields acetonitrile, and the hydrogen atom initiated decomposition of acetonitrile yields HCN. Aziridine, a predicted reaction intermediate, was not detected at 298 or 178 K. Oligomers of acetylene are also formed. Oligomers formed by the photolysis of ammonia in the presence of acetylene were shown by Fourier transform infrared spectroscopy to contain NH groupings and to differ from those produced by the direct photolysis of acetylene. The possible role of these photochemical processes on the formation of HCN and chromophores on Jupiter, Titan, and comets is discussed.

Two-photon formation of NH/ND(A 3Π) in the 193 nm photolysis of ammonia. II. Photolysis of NH 2

The formation ofNH(A 3Π) in the photolysis of NH 2 ‡ ( X 2B 1), internally excited ground state amidogen prepared by the 1 nm photnlysis of NH 3, has been studied. The alignment of the NH(A 3Π) was determined from the polarization of the NH (A 3Π→,X 3Σ −) fluorescence. The populations of the Λ-doublet states are found to be unequal with preferential population of the “antisymmetric” Λ-doublet. It is concluded that (i) the parent NH 2 ( X 2B 1) is rotationally excited, (ii) the dissociation i the NH 2(2 2A 1) state and (iii) the high rotational excitation of the NH(A 3Π) results from the rotational excitation of the NH 2 ‡( X 2B 1). NH (A 3Π) formed in the 193 nm photolyses of CH 3NH 2 and N 2H 4 and in the 172 nm photolysi generated by mechanisms similar to that in the 193 nm photolysis of NH 3.

Two-photon formation of NH/ND(A 3Π) in the 193 nm photolysis of ammonia. I. Mechanism and identification of the intermediate species

The mechanism for formation of the A 3Π states of NH and ND in the 193 nm photolyses of NH 3 and ND 3 has been investigated using two ArF excimer lasers in pump—probe experiments. The mechanism is shown to be sequential photolysis involving a long-living intermediate species. Rate constants have been measured for the quenching of these intermediates by their respective parent molecules and several other collision partners; the extrapolated zero pressure lifetimes are found to be > 100 μs. Fluorescences of the NH 2 and ND 2 excited states generated in these photolysis systems were also observed and found to decay bioexponentially. Rate constants were measured for the quenching of both the fast and slow components and the species emitting the longer-living component were found to be similar to the intermediates. Arguments are presented in favor of identifying the intermediates as internally excited NH 2(∼X) and ND 2(∼X).

Reaction between nitric oxide and the amidogen radical, NH2

The reaction between NO and NH/sub 2/ radicals produced from photolysis of ammonia has been monitored by FTIR spectroscopy in a low-temperature matrix for the first time. The results obtained show conclusively that nitrous oxide is a direct product of this reaction, which contrasts with previous gas-phase studies, where N/sub 2/ and H/sub 2/O are the cited primary products. /sup 15/N labeling of the ammonia produced /sup 15/N/sup 14/NO which excludes the possibility of either the HNO + HNO combination or the O(/sup 1/D/sub 2/) + N/sub 2/ reaction being of importance.

Generation of NH(a 1Δ) in the 193 nm photolysis of ammonia

We report the observation of NH(a 1Δ) formation in a one-photon process during the ArF laser (193 nm) photolysis of ammonia. We have used laser-induced fluorescence to detect NH(a) and ND(a) and report the rotational and vibrational populations generated. We have also reinvestigated the generation of NH(a) in the 248 nm photolysis of HN3 and find substantial vibrational excitation in contrast to the results of previous workers. We give estimates for the quantum yields for NH(a) and ND(a) in the photolysis of ammonia based on comparison with the yield in 248 nm photolysis of HN3.