NO Dimer Research Articles

The NO Dimer: II. Analysis of the ν1Band

Spectra of the symmetric ν1vibration of the NO dimer have been recorded in gas phase at low temperature, with a high-resolution infrared Fourier transform spectrometer. All the lines were least-squares fitted to a Voigt profile convoluted with the well-known apparatus function of the spectrometer. By means of this method, the frequencies of more than 109 new lines were measured. From the intensities of a set of 33 well-fitted and completely isolated lines, the transition moment was extracted. NO-broadening coefficients of the dimer lines were also measured as well as the predissociation time, which was found to be (2.65 ± 0.53) ns.

The cis and trans structures of the NO dimer cation

The NO dimer cation, (NO) 2 +, has been studied using high-level ab initio calculations. The ground state is determined to be the trans isomer, which has C 2h symmetry. The cis, C 2v, isomer lies ca. 100 cm −1 above this, as calculated at the RCCSD(T)/aug-cc-pVQZ(no g)//UQCISD/6-311+G(3df) level of theory. The equilibrium geometry of the trans isomer has an N–N bond length of 2.25 Å and a NNO bond angle of 112°. A reassignment of the ZEKE spectrum of the NO dimer is postulated on the basis of calculated harmonic vibrational frequencies.

Spectroscopic evidence for perturbed NO dimers on oxidized Mo(110)

We report herein the first direct experimental evidence of a nitric oxide dimer (NO)2 which is significantly perturbed from gas- and condensed-phase (NO)2 by bonding of one of the nitrosyls to a metal surface. Infrared reflectance absorbance spectroscopy of isotopically mixed overlayers is used to identify the formation of this species from NO adsorption on oxidized Mo(110) and to characterize it as a second-layer NO[ν(14NO)=1871 cm−1] bound to a surface nitrosyl [ν(14NO)=1728 cm−1], The spectroscopic signature of this species is a small (∼8 cm−1) splitting of ν(NO) of each of the nitrosyls upon isotopic mixing, rather than the appearance of three different frequencies for νs(NO) and νa(NO). The formation of such a dimer on oxidized Mo(110) does not result in N–N bond formation, in contrast to the evolution of both N3 and N2O via a dinitrosyl intermediate on the same surface. This result suggests that, on surfaces which interact strongly enough with NO to form chemisorbed nitrosyls stable above room temperature, N–N bond formation is favored by surface-bonding of both nitrosyls, rather than coupling via the weak N–N bond of a condensed-phase type (NO)2 dimer.

The NO dimer, 14N and 15N isotopomers isolated in nitrogen matrix: a near, mid and far infrared study

A near and far infrared study of 14NO– 14NO and its isotopomers, 14NO– 15NO and 15NO– 15NO, isolated in Nitrogen matrix was carried out. Infrared active fundamental vibrational modes, ν 1, ν 2, ν3 and ν 6, for each species of the cis NO dimer have been observed, as well as combination bands ν 1+ν 5 . The trans ON–NO form of the three isotopic species was also observed as well as the cis and trans ONON form.

The intermolecular vibrations of the NO dimer

The far infrared spectrum of the NO dimer in the gas phase has been observed for the first time, using a low temperature (100 K) long-path (180 m) absorption cell. The spectroscopic results are used, together with mid-infrared observations and high level CCSD(T) ab initio calculations, to locate the four low frequency intermolecular vibrational modes of (NO)2: ν2 (symmetric bend)=239.361 cm−1, ν3 (intermolecular stretch)=134.503 cm−1, ν4 (out-of-plane torsion)≈117 cm−1, and ν6 (antisymmetric bend)=429.140 cm−1. These values agree poorly with previous determinations based on condensed-phase spectra, indicating that there are large shifts in going from the isolated gas-phase dimer to the liquid, solid, or matrix-isolated environments.

Density functional study of the NO dimer using GGA and LAP functionals

The nature of the ON-NO bonding in the NO dimer still remains a challenge for currently available theoretical and experimental methods. Most of the theoretical studies reported so far predict a singlet cis ground state. However, the fully optimized geometry of the NO dimer may favor a triplet ground state, depending on the approximate method used. In this work we explore in detail the electronic structure of the fully optimized trans- and cis-NO dimer including a vibrational analysis in different electronic states, using several exchange-correlation functionals within the Kohn-Sham DFT method. The recently developed LAP exchange-correlation schemes that use the Laplacian of the density and the self-consistent kinetic energy density, improves significantly the results. The N-N bond distance is in better agreement with the experimental results, and the triplet/singlet gap is smaller, however, still predicting a triplet ground state. The nature of the electronic ground state is discussed in detail. We explored the possibility that in such a system the singlet ground state may be well approximated as a broken spin symmetry state with localized magnetic moments on each NO monomer aligned antiferromagnetically. A KS broken symmetry solution was thus obtained. However, the energy lowering due to the symmetry breaking was not sufficient to reverse the triplet/singlet energy ordering. The LAP functional avoids symmetry breaking out to larger distances than does the generalized gradient approximation (GGA). Although progress has been steady, the existing exchange-correlation functionals are not yet able to describe fully all aspects of this demanding system.

Nanospace geometry-sensitive molecular assembly

Interaction of a molecule with micropore walls strongly depends on the micropore width. Molecules confined in the micropore tend to form an intermolecular structure inherent to each molecule/pore system in order to lower the whole molecular energy. Supercritical NO is adsorbed in micropores of zolite or activated carbon fiber in the form of a dimer at 303 K. The NO dimerization varies with the micropore width. CCl 4 molecules only in pore of pore width =1.0 nm at 303 K form a plastic crystalline structure which is observed at 246–250 K in the bulk phase. H 2O molecules are associated with each other to form an ordered assembly in carbon micropores at 303 K; the smaller the pore width, the more ordered the assembly structure. The presence of preadsorbed H 2O noticeably enhances adsorption of supercritical CH 4 in carbon micropores at 303 K due to methane nanohydrate formation, which has an optimum pore width of 1 nm.

Nonadiabatic dynamics in polyatomic systems studied by femtosecond time-resolved photoelectron spectroscopy

We investigate the use of time-resolved photoelectron spectroscopy for studying nonadiabatic polyatomic dissociation dynamics. In particular, we emphasize the importance of the electronic structure of the ionization continuum in interpreting the results and provide an experimental example of these effects in the dissociation dynamics of the NO dimer.

The NO Dimer, 14N and 15N Isotopomers Isolated in Argon Matrix: A Near-, Mid-, and Far-Infrared Study

A near- and far-infrared study of 14NO−14NO and its isotopomers, 14NO−15NO and 15NO−15NO, isolated in argon matrix has been carried out. Infrared active fundamental vibrational modes, ν1, ν2, ν3, ν5, and ν6, for each species of the dimer have been observed, as well as overtone bands 2ν1, 2ν5 and combination bands ν1 + ν5, ν1 + ν6, ν5 + ν6, and ν4 + ν5. Frequency of the nonactive ν4 mode was also retrieved from combination bands. From the knowledge of the 18 available frequencies of the three isotopic species, force constants for the cis-ON−NO have been calculated. The force constants characterizing the N−N stretching mode and the ONN bending mode are found to be 0.39 mdyn/A and 0.42 mdyn A/rad2, respectively. The potential energy distribution calculated for each vibration showed that the ν2 and ν3 modes are strongly coupled and that there is no pure N−N stretching mode. In the same way, the ν1 mode could be considered as a pure NO stretching mode while the ν5 one is coupled to the ONN bending.

Chemisorption and Photoadsorption of NO on Cerium(IV) Oxide

CeO 2 showed high adsorptivity (4.9 molecules/nm 2 ) for NO at 303 K. The adsorbed species of NO on CeO 2 in the dark were the NO dimer and/or dinitrosyl, nitrosyl, and NO 2 - . About 40% of the NO adsorbed in the dark was chemisorbed mainly as NO 2 - . N 2 O seemed to be liberated into a gas phase via the intermediate species, such as the NO dimer. The UV irradiation to CeO 2 -NO systems at 303 K induced the photoadsorption of NO and the photocatalytic formation of N 2 O. Most of the photoadsorbed species were chemisorbed, mainly as photooxidized species, NO 2 - and NO 3 - ; all other photoadsorbed species were reversibly adsorbed as nitrosyl and dinitrosyl. A frequency shift was observed in a few IR bands of the adsorbed NO, which might have arisen from the photoreduction of Ce 4+ to Ce 3+ .

NO/Ni, NO/Ni2, and (NO)2/Ni2 Interactions. A Density Functional Study

Density functional methods were used to study the structural and vibrational properties of NO adsorbed on the Ni atom and Ni2 as well as the NO dimer ((NO)2) adsorbed on Ni2. (NO)2 is stabilized on Ni2 with an optimized N−N bond distance of 1.61 A. A bonding analysis was performed to understand the mechanisms of adsorption and of the stabilization of the NO dimer on Ni2. The significance of the stabilization of the NO dimer to the reaction path of NO adsorbed on metallic surfaces is also discussed briefly.

Millimeter-Wave Spectrum of the NO Dimer

The pure rotational spectrum of the NO dimer, (14N16O)2, has been studied in the 225–400 GHz millimeter-wave region by means of direct absorption in a supersonic jet expansion. Previously, only 4 rotational transitions of (NO)2had been measured in the microwave region. To these, we have added 66 new millimeter-wave transitions with values ofJranging from 4 to 16 and ofKafrom 2 to 7. Most transitions were observed as single lines, but a few showed partially resolved hyperfine structure. The analysis of these data, in combination with the previous microwave transitions and an extensive set of infrared (ν1band) measurements, has resulted in a greatly improved set of parameters for the ground state of the NO dimer, including the first sextic distortion parameters.

Cu−Dinitrosyl Species in Zeolites: A Density Functional Molecular Cluster Study

A small cluster model proposed earlier to examine bound Cu ions and their interaction with CO and NO in zeolites [Schneider, W. F.; Hass, K. C.; Ramprasad, R.; Adams, J. B. J. Phys. Chem. 1996, 100, 6032] is used to study Cu-bound dinitrosyl complexes. The possibility of a single-step, symmetric, concerted reaction occurring between the two nitrosyl ligands to form either a N−N bond or free N2 and O2 is addressed. Density functional theory is used to predict molecular and electronic structures and binding energies. N-down dinitrosyl binding to Cu0, Cu+, and Cu2+ can be represented as [Cu(I)−(NO)2-], [Cu(I)−(NO)2], and [Cu(I)−(NO)2+], respectively, with the dinitrosyl moiety closely resembling the free NO dimer, and having a long N−N bond (≈2.8 A). Dinitrosyl species bound to Cu through the O display two distinct binding modes, one resembling the N-down dinitrosyl binding, again with a long N−N bond (≈2.0 A), and the other similar to hyponitrite binding to a metal atom, displaying a short N−N bond (≈1.2 A)...

N 2O 2, N 2O 2− and N 2O 22−: structures, energetics and NN bonding

The density functional theory and the ab initio quantum chemistry methods, Becke3LYP and CASPT2, have been employed to determine structures and energetics of neutral and anionic N 2O 2 species. When going from a neutral NO dimer to an anionic species the NN bond lengths decrease drastically and the corresponding NN frequencies increase. The relative stabilities of the different N 2O 2 − isomers suggest an ONNO structure in a Trans configuration to be the most stable mono valent anion. The formation energies of 1.4–1.7 eV relative to the NO + NO − asymptote are in agreement with experiments. Excitation energies are determined and specific formation channels for three N 2O 2 − isomers are discussed. The hyponitrite ion, N 2O 2 2−, is also studied. Its total energy is 2.7–2.8 eV above the total energy of two NO −. In order to connect to an experimental study of NO adsorption on MgO the ability of two NO molecules to form a complex with Mg and Mg + is investigated.

The NO Dimer

The antisymmetric vibration ν5of the NO dimer was studied by high resolution infrared Fourier transform spectroscopy. The dimer was produced at thermodynamical equilibrium, in the temperature range 127–154 K, in a White-type multipass cell for NO pressures ranging from 26 to 88 mbar. The upper level spectroscopic constantsA′,B′, andC′ of the dimer could be measured from the spectra. An estimate of the lifetime of the excited state was made possible from the measurement of the anomalously large linewidths. The binding energyD0was also derived from the intensities of the three branches of theA-type transition recorded at various temperatures; the obtained value ofD0is in good agreement with results reported in previous studies.

The v5 band of the NO dimer

The v₅ band of the NO dimer

Metal complexes with unusual ligands: Mg +.(NO) n

A ‘pick-up’ technique has been used to generate Mg +.(NO) n cluster ions for n in the range 3 to 20. Mass spectrometric measurements of the intensities and fragmentation patterns of individual ions reveal that the clusters have a central core of the form Mg +.(NO) 7 and that additional molecules favour the formation of NO dimers. Taking NO as a 1-electron donor, composition of the core can be rationalised in terms of the formation of a stable eight-electron closed-shell unit.

Matrix isolation and theoretical studies of ONNO: Assignment of a new combination band and density functional calculations

An investigation of the nitric oxide dimer was conducted utilizing the matrix isolation technique coupled with Fourier transform infrared spectroscopy. A previously unreported absorption in matrices at 3609 cm −1 was observed and has been assigned to the NO dimer. This new absorption has been assigned as a combination band arising from the ν 1 and ν 5 stretches at 1866 cm −1 and 1776 cm −1, respectively. Density functional theoretical (DFT) calculations were also performed to determine the optimized structures and relative energies of the cis- and the trans-ONNO. The potential energy surface for isomerization via N-N bond torsion was also calculated predicting barriers to isomerization of 30.8 and 8.0 kJ/mol.

Differential cross sections for rotationally inelastic collisions of NO(2Π1/2, j′⩽2.5) with NO(2Π1/2, j′⩽2.5) at a kinetic energy of 442 cm−1

We report crossed molecular beam measurements of state-resolved differential cross sections for NO+NO collisions at relative kinetic energy of 442 cm−1. The initial state (NO 2Π1/2v=0,j⩽2.5) was prepared in both beams by pulsed supersonic expansion of pure NO gas. Scattered products were detected by resonance enhanced two-photon ionization. NO product distributions were measured in both scattering angle and final rotational state. Intensity maxima were found in both types of scans, and comparable populations were found in both of the spin-orbit manifolds (2Π1/2 and 2Π3/2). The results obtained here are compared to previous NO+Ar scattering experiments and theory, NO dimer studies, and NO+NO bulb kinetics experiments.

The v<SUB>5</SUB> band of the NO dimer

The v<SUB>5</SUB> band of the NO dimer