Excited NO Molecules Research Articles

Fluorescence of NO A 2Σ +(υ′= 5), B 2Π(υ′= 8) and C 2Π(υ′= 1) excited by iodine atomic lines

NO was irradiated by a low-pressure iodine discharge lamp which induced fluorescence from excited NO molecules. From analysis of fluorescence spectra it was found that the A 2Σ +(υ′ = 5), C 2Π(υ′ = 1) and B 2Π(υ′ = 8) states were excited by iodine atomic lines at 179.9, 183.0 and 187.6 nm, respectively. By comparing undispersed fluorescence intensities of NO with an without N 2, the predissociation of A 2Σ +(υ′ = 5) was estimated to be much weaker than that of B 2Π(υ′ = 8) or C 2Π(υ′ = 1).

The dynamics of the infrared multiphoton pumping of optically excited NO2 molecules

The infrared multiphoton (IRMP) pumping of optically excited NO2 molecules is investigated. From changes in the fluorescence emission spectrum due to the IRMP pumping, both the fraction of the NO2 molecules that has dissociated, as well as the fraction that remains within one IR photon in energy below the dissociation limit, are deduced. This has made possible the first direct measurements of the final, dissociative step in the IRMP pumping of molecules, and of IRMP stimulated emission. The dynamics of the IRMP pumping is studied by systematically varying the optical excitation energy. The results are compared with numerical solutions to the well-known rate equation model for the IRMP pumping of polyatomic molecules. From this comparison the best fit transition cross sections connecting various energy regions in highly vibrationally excited NO2 molecules were deduced. Except for the final, dissociative transition, they depend significantly on both laser intensity and pulse width for intensities as large as 10 GW/cm2 and pulse widths as short as 500 ps. These dependences are probably due to the sparse density of vibrational states in such a small molecule as NO2. In addition, the rotational energy present in room temperature NO2 can enhance considerably the IRMP dissociation probability of optically excited NO2.

Energy transfer in collisions of excited Na atoms with NO molecules

Measurements of scatterng angle and product velocity distributions are reported for a crossed molecular beam study of excited Na atoms and NO molecules. These results provide evidence that most of the electronic energy is partitional between relative translation and vibration f the NO molecule. (AIP).

Energy transfer in monochromatically excited nitric oxide: A2Σ+ and B2Π

Excitation of NO molecules into specific vibration-rotation levels of the A2Σ+ and B2Π electronic states by absorption of atomic lines has been studied under various experimental conditions by observing the steady-state fluorescence spectra of the (A 2Σ+−X 2Π) and (B 2Π−X 2Π) bands. Excitation of the A 2Σ+, v′=0–3 and B 2Π, v′=3, 4 levels was achieved. The fluorescence from NO A 2Σ+, v′=0–3 was found to be quenched by NO X2Π with an effective cross section of 25 Å2. The fluorescence from NO B 2Π, v′=0, 3, 4 was found to be quenched by NO X2Π with effective cross sections of 16, 21, and 20 Å2, respectively. The anomalously efficient vibrational relaxation of NO A 2Σ+, v′=1 by NO X2Π was found to be one aspect of an efficient electronic energy exchange process. The cross sections for exchange of electronic energy between N14O16 A Σ+2, v′=0 and 1 and N1615 OX 2Π, v″=0 were found to be 12 ± 3, 7 ± 4, and 1.7 ± 0.3 Å2 for the N14O16 A, v′=1→N15O16, A, v′=1,N14O16 A, v′=0→N15O16 A, v′=0, and N14O16 A, v′=1→N15O16 A, v′=0 processes, respectively. A transition dipole-transition dipole interaction is proposed for this transfer process. Rates of electronic energy transfer from NO A2Σ+ to NO B2Π, and vice versa, in collision with NO X2Π, were also measured.

Molecular predissociation of nitrogen dioxide studied by fluorescence excitation spectroscopy

In a steady-state experiment, fluorescence efficiency of the electronically excited nitrogen dioxide has been measured in the pressure range of 1–1000 mTorr and in the exciting wavelength range of 3800–5200 A using 0.1–1.0 A resolution. It was found to be independent of the exciting wavelength in the 4150–5200 A range, but began to decline sharply below 4150 A. Since the dissociation limit of the ground state NO2 giving the ground states of NO and O corresponds to 3979 A, this early onset of “predissociation” is attributed to the utilization of the rotational energy in overcoming the dissociation threshold. Probable radiationless transitions involving the excited NO2 molecules are discussed in light of the higher resolution data on the fluorescence excitation efficiencies.

Energy levels of NO + ion by He and Ar resonance lines photoelectron spectrometry

The high-resolution photoelectron spectrum of NO obtained with He 584 and Ar 1048–1067 lines is discussed. Eight ionic electronic levels reported by others are confirmed and six ionic ground vibrational frequencies are measured. Vibrational enhancement of the ground ionic X 1Σ + state observed with Ar lines is explained by the preionization of excited NO molecules, known by photoionization, in their ν′  1 and ν′  2 vibrational levels.

Photodissociation of NOCl and NO2 in the Vacuum Ultraviolet

AbstractThe photodissociation of NOCl and NO2 in the vacuum ultraviolet yields the electronically excited NO molecule which fluoresces in the near ultraviolet. The fluorescence spectrum, which lies mostly in the region 2200‐4000 Å, extends below 2200 Å as the wavelength of incident light decreases. This is interpreted in terms of the production of the NO C2Π, D2Σ+, B2Δ, E2Σ+ along with the production of the NO A3Σ+, B2Π. The fluorescence intensity and the yield have been measured as a function of incident wavelength. The fluorescence curves thus obtained are correlated with the absorption spectrum. The absorption coefficient of NOCl in the region 1100‐2200 Å has been measured. The absorption spectrum of NOCl between 1100 and 1700 Å may be divided into three regions, respectively, corresponding to transitions providing the NO A2Σ+, NO C2Π, D2Σ+ and NO B′2Δ, E2Σ+ with a simultaneous production of the ground state NO or other products. The absorption by NO2 in the spectral region from 1100‐1450 Å involves transitions yielding the NO A2Σ+, B2Π, NO C2Π, D2Σ and NO B'2Δ, E2Σ+ below their respective threshold wavelengths of incident light. Besides it has another transitions giving products other than the electronically excited NO. The threshold energy of the incident photon producing the NO A2Σ+ B2Π gives an upper limit of bond dissociation energy. The bond energies obtained are D(NO‐Cl) ≤ 1.77 ± 0.05 eV and D(NO‐O) ≤ 3.22 ± 0.05 eV which are 0.17 eV and 0.10 eV higher than the respective values obtained from the heat of formation.

Level crossings C 2Π ∽ B 2Π and F 2Δ ∽ B' 2Δ and the lasering combination transition B' 2Δ - C 2Π of the no-molecule

A peculiar level configuration in the excited NO-molecule, claimed to be related to an observed laser action, is discussed.

Laser transition with predissociation lower state in the no molecule

Vibrational relaxation of NO molecules excited by a pulsed e-beam sustained discharge (EBSD) with the use of CO laser probing was studied. We developed numerical model of vibrational kinetics in ensemble of NO molecules due to comparing the experimental and calculated data on absorption dynamics of vibrational excited NO molecules.

Mechanism of chemiluminescent combination reactions involving oxygen atoms

The intensities I c and I a respectively of chemiluminescent emission by CO 2 in the O+CO reaction and by NO 2 in the O+NO reaction have been measured from 200 to 300 °K in a fast flow system. Both I a and I c were found to obey an expression of the type I = I 0 [O] [XO], where I 0 was independent of total pressure over a similar range of low pressures. I 0c was found to depend on the nature of the inert gas M used as carrier. I 0a was found to have a small negative temperature coefficient similar to that of the overall reaction O + NO + M -> NO 2 + M . (1 a ) I 0c had a positive activation energy of 3.7 + 0.5 kcal/mole. The pre-exponential factors of I 0a and I 0a were similar and the rate constant at 293° K for the overall combination O + CO + M -> CO 2 + M (1 c ) was less than 0.002 of that of reaction (1 a ). The chemiluminescent reactions proceed via three body processes, since I 0 and k 1 showed dependences on the nature of M for both the O + NO and O + CO reaction. A considerable fraction of the product molecules formed in both reactions is produced through the excited state from which emission occurs and the negative temperature coefficients of k 1a and I 0a are apparently due to redissociation of excited NO 2 molecules from vibrational levels close to the dissociation limit. O + NO are stabilized into an excited state of NO 2 by a third body. This state, which is the one responsible for the predissociation in the NO 2 absorption spectrum , crosses the state from which emission occurs and into which excited NO 2 molecules undergo rapid radiationless transitions. A similar radiationless transition occurs between triplet CO 2 molecules formed in the initial combination step and the singlet state from which emission to the ground state ( 1 E + g ) takes place. Spin reversal in the O + CO reaction is therefore not a rate-controlling step for light emission nor for combination, and the activation energy observed for I 0c is due to the presence of an energy barrier over which the CO 2 molecule must pass to reach the stable triplet state.

Excitation of the auroral green line in nitrogen afterglow

Production of the auroral green line of OI ( 1D −1S , 5577 Å) is observed during long (30 sec) afterglows in a static system containing nitrogen and small amounts of oxygen. Relative to the intensities of the N 2 1st positive bands, the measured intensities of 5577 Å and the NO β bands increase with time. The long period of observation definitely eliminates the initial discharge as a possible source of the metastable oxygen atoms, and their chemical excitation in the afterglow volume is established. A probable process consistent with observations is that involving collision of N atoms with vibrationally excited NO molecules. This mechanism is discussed as a possible source of 5577 Å in the airglow.

Excitation of the Auroral Green Line in Nitrogen Afterglows

Production of the auroral green line of OI (1D—1S, 5577 A) is observed during long (30-sec) afterglows in a static system containing nitrogen and small amounts of oxygen. Relative to the intensities of the N2 1st positive bands, the measured intensities of 5577-A and the NOβ bands increase with time. The long period of observation definitely eliminates the initial discharge as a possible source of the metastable oxygen atoms, and their chemical excitation in the afterglow volume is established. A probable process consistent with observations is that involving collision of N atoms with vibrationally excited NO molecules. This mechanism is discussed as a possible source of 5577 A in the airglow.

On the Pressure Broadening in the Gamma Bands of Nitric Oxide

A quantitative reinvestigation of the pressure broadening in the γ(0,0) and γ(1,0) bands of nitric oxide has established that the pressure effect is not abnormal as has sometimes been supposed and that the collision diameter of the excited NO molecule is approximately 3.8 A.