Vibrationally selective electronic energy transfer from metastable xe atoms to N2 and CO molecules

Formation of N₂(B) and CO(a', d) by collisions with Xe(³P_0,2) has been studied in the energy range 50–700 meV_c.m using crossed beams and beam/gas apparatus. Well-resolved product emission spectra were observed which showed high vibrational state specificity and low rotational excitation. These features are explained using semi-empirical interaction potentials.     

Vibrational energy relaxation in liquid N2CO mixtures

The vibrational energy relaxation rates of the liquid nitrogenCO system have been measured by optically pumping the collision-induced fundamental vibrational absorption band of liquid N₂ with the output of an HBr TEA laser. A radiatively dominated value of 56 ± 10 s is found for the intrinsic nitrogen relaxation time. The CO contribution to the decay rate is explained on the basis of a simple kinetic model and found also to be radiatively dominated at low CO concentrations. The importance of radiative trapping and energy transport in evaluating the lifetimes is demonstrated.     

Kinetic energy spectra of N2+ photofragments in the laser photodissociation of N2O+

Using a ZAB-2F double-focusing mass spectrometer together with an argon-ion laser, the kinetic energy spectra of N₂⁺ photofragments from the photodissociation of N₂O⁺ have been measured at wavelengths 514.5, 496.5, 488.0 and 476.5 nm in the visible region of the spectrum. Energies released in the centre-of-mass frame of reference are given. From the results it is deduced that the states involved in the absorption and dissociation processes ar probably N₂O⁺(B̃²Π) v ⩾ 3 and N₂O⁺ (C̃²Σ⁺) v ⩾ 0, respectively.     

Fine structure of the X-ray spectra of molecules K-absorption spectra of the CO and N2 molecules

Journal of Structural Chemistry -     

Potential energy surfaces and vibrational spectra for isotopomers of N2O

Potential energy surfaces and vibrational spectra for the four isotopomers (^l5N¹⁴N¹⁶O,^l4N^I5N¹⁶O,¹⁵N₂ ¹⁶O and¹⁵N₂ ¹⁸O) of N₂O have been investigated with the vibrational self-consistent field-configuration interaction method. It is shown that the isotopomers with the same end atom have similar values of the potential parameters, and that substitution with different end atoms can affect the potential obviously. The calculated vibrational levels are in good agreement with the observed values by the optimization of several potential parameters (f ₁ ⁽¹⁾,f ₁₃ ⁽⁰⁾,f ₃ ⁽¹⁾ which are sensitive to isotopic substitutions. Project supported by the National Natural Science Foundation of China (Grant No. 29673029).     

Unraveling the origin of band shapes in infrared spectra of N2O-12CO2 and 12CO2-13CO2 ice particles

Band structures in the region of strong infrared absorption bands for different N2O-12CO2 and 12CO2-13CO2 composite particles are investigated by combining quantum mechanical exciton calculations with systematic experimental investigations. The ice particles are generated by collisional cooling and characterized with rapid-scan infrared spectroscopy. The size of the particles lies between approximately 10 and 100 nm. The calculated spectra show excellent agreement with the experimental data. This work leads to a detailed understanding on a molecular level of shape effects in pure and statistically mixed particles as well as of the characteristic features observed for core-shell particles.     

Time-resolved excitation spectra of xenon vapor in the 1500 Å region

Time-integrated and time-resolved excitation spectra, as well as fluorescence lifetimes, have been measured for xenon vapor as a funtion of pressure (for pure xenon as well as with different collision partners: krypton and helium), monitoring the 1700 Å second continuum afterglow. Three very different decay components have been observed: (a) A short component with lifetimes of the order of 2 ns, which is attributed to emission from the upper vibrational levels of the O⁺_u(¹Σ⁺_u) state of Xe*₂. (b) A long component with τ ≈ 60 ns, corresponding to emission from thermally relaxed vibrational levels of the 1_u,O^?_u(³Σ⁺_u) states of Xe*₂. No intervention of any Xe atomic excited species is invoked to explain the excitation and deactivation processes of Xe₂ molecules for these two components of the fluorescence. (c) A very long component with lifetimes in the 150–500 ns range, having a broad ? 1000 cm^?1 - excitation band, centered at ≈ 1470 Å and showing a striking screening and self-absorption effect as well as a strong effect when the partial pressure of a collision partner (Kr, He) is increased. The mechanism of this last excitation is not yet very well understood.     

Semiclassical calculations of collision line broadening in Raman spectra of N2 and CO mixtures

We present a detailed theoretical study of pressure-broadened Raman line shapes in binary mixtures of nitrogen and carbon monoxide. The semiclassical Robert-Bonamy theory was used to calculate self-broadened Q-branch linewidths of N(2) and CO, and Lennard-Jones (LJ) potential energy surface parameters were fixed by comparing our results with extensive experimental linewidth data. For the case of N(2), the ab initio PES8 potential energy surface was investigated, however, the anisotropic repulsive part had to be reduced to ensure a good agreement with experimental linewidths. The agreement between calculations and experiments was remarkably good, both for self-broadened N(2) and CO Q-branch linewidths. Yet, our calculations were not able to predict the experimentally observed difference between Q- and S-branch linewidths of self-broadened N(2). The central results of this work are the Q-branch linewidths of N(2)-CO and CO-N(2), which have been calculated through an extrapolation of the parameters of the potential energy surfaces used for self-broadened linewidths by common combination rules.     

Vibration–Vibration energy exchange between N2O and CO

The temperature dependence of the vibration–vibration energy transfer between the v₃ mode of N₂O and the first vibrational level of CO was determined over a range of 780 to 1400°K using a shock tube. Several mixtures of CO-N₂O were tested, diluted in 95% Ar. The Landau–Teller plot of the vibration–vibration relaxation times has a least squares line of where pτvv is in atm ˙μsec and T in °K. The measured kinetic reaction was determined to be The transfer probabilities for this process were found to vary directly with temperature.     

Computed lifetimes of metastable states of CO2+

Highly correlated internally contracted multireference configuration interaction wave functions are used to calculate the potential energy and spin-orbit coupling functions for the lowest electronic states of CO2+ dication. Using these functions, the positions and lifetimes of the corresponding vibronic states are evaluated by means of log-phase-amplitude, stabilization, and complex-scaling methods within the framework of a multichannel Schrodinger analysis. For the first time in the literature, the calculated lifetimes are in good agreement with the experiment, thereby proving the reliability of the predicted characteristics and adequacy of the used theory for a theoretical study of other molecular dications.     

Analysis of low energy X-ray and excitation spectra of Ba 35+

We present a theoretical analysis of the low energy X-ray spectra of the Ba³⁵⁺ + e ^- system, in the energy region below 2 keV, for comparison with future experiments. In a recent study carried out at the National Institute of Standards and Technology, scandium-like Ba³⁵⁺ ions were created, trapped and excited using an Electron Beam Ion Trap and an electron beam with kinetic energy of 2.35 keV. The theory agrees well with experiment for X-ray energies in the region 2–5 keV. The experiment also gives evidence suggestive of a large cross section for X-ray production in the region below 2.0 keV. We include the contribution to the X-ray spectra of collisional excitation followed by fluorescence decay, radiative cascade processes, M-shell dielectronic recombination, Bremsstrahlung, and a new off-shell, quasi-resonant continuum dielectronic recombination process. We find that excitation fluorescence is the dominant process, with smaller contributions from the other radiative cascade processes as well as a continuous Bremsstrahlung background.     

Reconstruction of the free energy in the metastable region using the path ensemble

By quenching into the metastable region of the three-dimensional Ising model, we investigate the paths that the magnetization (energy) takes as a function of time. We accumulate the magnetization (energy) paths into time-dependent distributions from which we reconstruct the free energy as a function of the magnetic field, temperature, and system size. From the reconstructed free energy, we obtain the free-energy barrier that is associated with the transition from a metastable state to the stable equilibrium state. Although mean-field theory predicts a sharp transition between the metastable and the unstable region where the free-energy barrier is zero, the results for the nearest-neighbor Ising model show that the free-energy barrier does not go to zero.     

Microwave spectra, structure, and dynamics of the weakly bound complex, N2 CO2

The Fourier transform microwave spectra of the various isotopologs of the weakly bound complex of carbon dioxide with the most abundant molecule in the atmosphere, nitrogen, have been measured. The structure of the complex has been determined and evidence for the inversion of the N(2) is presented. The molecule is T-shaped, with the OCO forming the cross of the T, a structure consistent with that deduced from a previous rotationally resolved infrared experiment. A significant wide-amplitude bending motion of the N(2) is deduced from the values of the (nearly identical) nuclear quadrupole coupling constants of the nitrogen nuclei. The spectroscopic results are compared with high-quality ab initio calculations. We examine the consequences of the N(2) CO(2) complex formation in the atmosphere upon the greenhouse warming potential of carbon dioxide.     

The metastable spectra of cis- and trans-butenes

A new type of ion detector has been developed that can be made to operate in two ways. It can detect all ions, or it can be made to detect only those within a preselected energy range. Its use on a mass spectrometer to examine the metastable spectra of cis- and trans-butenes is described.     

Classical trajectory study of rotational excitation in low energy HeCO and HeH2 collisions

Classical trajectory calculations for the rotational excitation of CO and H₂ by collision with He have been carried out and compared to the accurate quantum mechanical calculations of other workers. The agreement is reasonably encouranging, although some inherent limitations of this strictly classical approach are observed and discussed.