75-13-8Relevant academic research and scientific papers
Photochemistry of HNCO in Solid Xe: Channels of UV Photolysis and Creation of H2NCO Radicals
Pettersson, Mika,Khriachtchev, Leonid,Jolkkonen, Santtu,R?s?nen, Markku
, p. 9154 - 9162 (1999)
Photolysis of HNCO at wavelengths between 266 and 193 nm is studied in solid Xe with FTIR and laser-induced fluorescence methods. The channels HNCO → H + NCO (a) and HNCO → NH + CO (b) are operative in a Xe matrix. Channel b produces both isolated fragments and NH?CO complexes as characterized by the CO absorption. The MP2/6-311++G(3df,3pd) calculations are presented for the NH-CO complexes and compared with the experimental data. Photolysis of NCO produces mainly NO + C. A part of the carbon atoms form C2 after which C2- is created in a photoinduced charge transfer reaction. For comparison, in solid Kr, photolysis of HNCO produces additionally HOCN but this channel is absent in a Xe matrix. Upon annealing of the partially photolyzed matrix at 50 K, hydrogen atoms are mobilized and a radical H2NCO is formed by a reaction of a hydrogen atom with a HNCO molecule. Four IR absorptions of H2NCO are observed and they agree well with the MP2/6-311++G(3df,3pd) calculations. The assignment is supported by experiments with DNCO. The threshold for the photodecomposition of H2NCO is between 365 and 405 nm.
Reactivity of HNCO with NH3 at low temperature monitored by FTIR spectroscopy: Formation of NH4+OCN-
Raunier, Sebastien,Chiavassa, Thierry,Marinelli,Allouche,Aycard
, p. 594 - 600 (2003)
The reactivity of isocyanic acid (HNCO) with solid ammonia (NH3) was first studied at 10 K, using FTIR spectroscopy. The ammonium isocyanate (NH4+OCN-) is formed from a reaction between HNCO and NH3. Vibrational band assignments for NH4+OCN- have been given. On the other hand, when HNCO is adsorbed on amorphous NH3 film, the reaction does not occur. Warming up of this sample at 90 K induces the NH4+OCN- formation. Quantum calculations showed that the solvation of NH3 directly bonded to HNCO by at least three NH3 molecules plays a major role in the NH4+OCN- formation process and confirmed the spontaneous character of this reaction.
Photodecomposition of N-hydroxyurea in argon matrices. FTIR and theoretical studies
Saldyka, Magdalena
, p. 1922 - 1932 (2013)
The photochemistry of N-hydroxyurea in solid argon has been investigated by FTIR and ab initio calculations. The irradiation of the NH2CONHOH/Ar matrices with the full output of the Xe arc lamp leads to the formation of the HNCO-NH2OH and N2-H2O-CO complexes. For the isocyanic acid-hydroxylamine complex, the spectra prove the existence of the hydrogen bonded structure with the NH group of HNCO attached to the oxygen atom of the NH2OH molecule. Two structures were identified for the nitrogen-water-carbon monoxide complex. In the first one, water is hydrogen bonded to the carbon atom and interacts with the nitrogen atom through van der Waals forces. In the second structure, water serves as a proton donor toward the nitrogen and carbon atoms of N2 and CO molecules, respectively. The identification of the products is confirmed by deuterium substitution and by MP2 calculations of the structure and vibrational spectra of the identified complexes.
Simultaneous derivatization and trapping of volatile products from aqueous photolysis of thiamethoxam insecticide.
Schwartz,Sparrow,Heard,Thede
, p. 4671 - 4675 (2000)
An aqueous photolysis study was conducted with radiolabeled thiamethoxam, 4H-1,3,5-oxadiazin-2-imine, 3-[(2-chloro-5-thiazolyl)methyl]tetrahydro-5-methyl-N-nitro, to establish the relevance of aqueous photolysis as a transformation process for (14)C-[thiazolyl]-thiamethoxam. (14)C-[thiazolyl]-thiamethoxam was applied to sterile sodium acetate pH 5 buffer solution at a dose rate of approximately 10 ppm. The resulting samples were incubated for up to 30 days at 25 degrees C under irradiated and nonirradiated conditions. The irradiated samples were exposed to a 12-hour-on and 12-hour-off light cycle. Volatile fractions accounted for up to an average of 56.76% of the total dose for the irradiated incubations and a mixture of carbonyl sulfide (COS) and isocyanic acid (CONH). Verification of these components was accomplished by trapping with cyclohexylamine and formation of the thiocarbamate and the isocyanic acid derivatives. A similar method of trapping thiocarbamate metabolites was reported (Chen and Casida, 1978) where filter paper saturated with isobutylamine in methanol was arranged to trap (14)COS and (14)CO(2) under a positive flow of O(2) at 25 degrees C. Mass spectroscopy of the derivatized components confirmed the presence of carbonyl sulfide as the cyclohexylamine thiocarbamate and of isocyanic acid as its cyclohexylamine derivative. Evidence from this study indicates that thiamethoxam degrades significantly under photolytic conditions.
The formation and hydrolysis of isocyanic acid during the reaction of NO, CO, and H2 mixtures on supported platinum, palladium, and rhodium
Cant,Chambers,Angove
, p. 11 - 22 (2001)
The extent to which isocyanic acid (HNCO) is formed during the reaction of NO/CO/H2 mixtures over silica-supported Pt, Rh, and Pd was studied with the subsequent hydrolysis of HNCO on oxide systems placed downstream. HNCO formation was a characteristic feature of the NO + CO + H2 reaction over silica-supported Pt, Rh, and Pd. Platinum produced the largest quantity in two stages, i.e., from H2 and then using NH3 being formed as a coproduct. With Pd, HNCO arose largely from NH3 alone because H2 was totally removed by reaction with NO at low temperature. Rhodium gave rise to the least HNCO. Formation was confined to a narrow temperature area due to the coincident consumption of H2 and NO, which precluded NH3 reaction with CO and NO. Hydrolysis of HNCO to NH3 and CO2 was appreciable on SiO2 alone and faster when a metal was present. Other oxide systems gave complete hydrolysis to the limit of the water present and total reaction with even small excesses of water. The possible presence of HNCO in vehicle exhaust was not an issue since the presence of a vast excess of steam and an active washcoat in three-way converters would ensure complete hydrolysis. However, the latter process might contribute to ammonia emissions at moderate temperatures under conditions where CO is still present.
An experimental and theoretical study of the HNCO+ ion
Wilsey,Thomas,Eland
, p. 21 - 36 (2000)
The dissociations of energy-selected HNCO+ ions have been examined at ionisation energies up to 40 eV using photoelectron-photoion coincidence spectroscopy. The slow metastable dissociation to HCO+ is shown to occur from initial population of low vibrational levels within the doublet states corresponding to the third photoelectron band. Rate constants for the dissociation from several levels have been measured and the existence of an optical emission is predicted. High level calculations identify the third band in the photoelectron spectrum as an overlay of almost degenerate states arising from ionisation of the in-plane and out-of-plane bonding π-orbitals. The calculations suggest that at energies between 15.5 and 16 eV, the dominant pathway for dissociation involves slow internal conversion to the ground doublet state without surface crossing, followed by intersystem crossing to the quartet surface. At energies over 16 eV, two mechanisms are possible; intersystem crossing from the second excited doublet state to the lowest quartet surface in a cis-bent configuration, or internal conversion to the first excited doublet state via a surface crossing in the same region, followed by a second nonradiative transition to the doublet ground state and intersystem crossing to the quartet surface. In each case, the initial step is expected to be slow, consistent with the existence of an optical emission, and H-atom transfer occurs on the quartet surface via a 'loose' transition state leading to the direct formation of HCO+ and N(4S(u)). (C) 2000 Published by Elsevier Science B.V.
Initial state resolved electronic spectroscopy of HNCO: Stimulated Raman preparation of initial states and laser induced fluorescence detection of photofragments
Brown, Steven S.,Berghout, H. Laine,Crim, F. Fleming
, p. 8985 - 8993 (1997)
Stimulated Raman excitation (SRE) efficiently prepares excited vibrational levels in the ground electronic state of isocyanic acid, HNCO. Photofragment yield spectroscopy measures the electronic absorption spectrum out of initially selected states by monitoring laser induced fluorescence (LIF) of either NCO (X 2II) or NH (a 1Δ) photofragments. Near threshold, the N-H bond fission is predissociative, and there is well-resolved rotational and vibrational structure in the NCO yield spectra that allows assignment of Ka, rotational quantum numbers to previously unidentified vibrational and rotational levels in the ν1 N-H stretch and ν3 N-C-O symmetric stretch fundamentals in the ground electronic state of HNCO. The widths of NCO yield resonances depend on the initial vibrational state, illustrating one way in which initial vibrational state selection influences dissociation dynamics. Initial excitation of unperturbed ν1 (N-H stretch) states leads to diffuse NCO yield spectra compared to excitation of mixed vibrational levels. The higher energy dissociation channel that produces NH (a 1Δ) has coarser structure near its threshold, consistent with a more rapid dissociation, but the resonance widths still depend on the initially selected vibrational state.
Internal Energy Distribution of the NCO Fragment from Near-Threshold Photolysis of Isocyanic Acid, HNCO
Brown, Steven S.,Berghout, H. Laine,Crim, F. Fleming
, p. 7948 - 7955 (1996)
We report the first measurement of the vibrational- and rotational-state distributions in the NCO fragment resulting from photolysis of HNCO.Recent studies have drawn conclusions about the photochemistry of HNCO and the vibrational distribution in the NCO fragment from observations of the kinetic energy distribution of the H atom produced in this photolysis; however, there has been no direct observation of the NCO fragment itself.We use laser-induced fluorescence to detect the nascent NCO photoproducts and spectral simulations to extract vibrational-state populations.The rotational distributions, where we can measure them, show little excitation, and the vibrational energy preferentially appears in the bending mode.The vibrational-state distribution results directly from the excited-state geometry of the HNCO parent, in which the NCO group is bent.The dissociation proceeds from this bent NCO group to a linear NCO fragment, strongly exciting the bending mode.We find about 65percent of the total energy in relative translation of the fragments, while 30percent goes into vibration and 5percent into rotation of NCO.
Kinetic Study of the Thermal Decomposition of Isocyanic Acid in Shock Waves
Kajimoto, Okitsugu,Kondo, Osamu,Okada, Kazuo,Fujikane, Jiro,Fueno, Takayuki
, p. 3469 - 3474 (1985)
Thermal decomposition of isocyanic acid HNCO diluted to less than 2.0 molpercent in argon was studied behind incident shock waves over the temperature range 2100-2500 K.The decomposition course was followed by monitoring the light absorption of HNCO and NH(3Σ-) at 206 and 336 nm, respectively.It is confirmed that the primary step of the decomposition is a bimolecular process HNCO+Ar->NH(3Σ-)+CO+Ar, ΔH00=337 kJ*mol-1, with the low pressure limit rate constants k=E17.23+/-0.36 exp-1/RT>cm3*mol-1*s-1.The singlet-to-triplet crossing po int is estimated on the basis of the RRKM low-pressure-limit rate constant calculations.The overall decomposition mechanism is suggested and its validity is confirmed by computer simulation of the time-concentration profiles of NH(3Σ-) at varying temperature.
Photodissociation Studies of HNCO: Heat of Formation and Product Branching Ratios
Spiglanin, Thomas A.,Perry, Robert A.,Chandler, David W.
, p. 6184 - 6189 (1986)
The heat of formation (ΔHf(298 K)) of HNCO is determined to be -24.9+0.7-2.8 kcal/mol (based on ΔHf(NH) = 85.2 kcal/mol).This value is obtained by measuring the threshold for the production of NH(a1Δ) and by determining the energy contents of the NH fragment and the CO cofragment produced by photolysis of HNCO at wavelengths near the threshold.Saturated laser-induced fluorescence is used to determine the internal state distribution of NH(a1Δ), and multiphoton ionization is used to measure the internal state distribution of CO.An upper limit for the branching ratio of NCO/NH production from photodissociation of HNCO at 193 nm is determined from an analysis of kinetic experiments to be 0.10.To clarify the mechanism of photodissociation, HNCO fluorescence-excitation and NH(a1Δ) action spectra are also measured.They imply that two excited states of HNCO are present where only one had previously been considered.
