Population Of Vibrational Levels Research Articles

An Analysis of the CF2 Emission Spectrum in a CF2Cl2 Plus Metastable He System

Abstract Ultraviolet chemiluminescence caused by a reaction of metastable He and CF2Cl2 was observed. Laserexcited single-vibronic-level fluorescence of the CF2 ？dical thus produced was also examined. The main feature in the 250–400 nm region was explained as the CF2 \ ildeA1B1-\ ildeX1A1 transition. The observed vibrational-level population of CF2(\ ildeA1B1) resulting from this reaction exhibits a maximum near v′2=5. This fact implies that the product has a FGF angle of about 104°, which is nearly equal to the FCF angle (105.4°) of the reactant (CF2Cl2) molecule, rather than to the equilibrium FCF angle (122°) of the CF2 (\ ildeA1B1) itself.

Energy transfer between biacetyl and iodine in the gas phase

Quenching of biacetyl phosphorescence by molecular iodine is very efficient. The energy transfer rate constant ((7.7 ± 0.5) × 10 6 Torr −1 s −1) indicates that biacetyl is deactivated on every collision. Dissociation of iodine is indicated as well as population of the B 3Π 0u+ state. A broad emission centred around 580 nm appears in the mixture. The assignment to the B state requires a non-statistical distribution of the vibrational level population.

Near resonant vibration → vibration energy transfer under single collision conditions

Collisional energy transfer from energy levels ?1900 cm−1, produced by IR multiphoton absorption, C3H2O(v≳1)+M→C3H2O(v=1)+M°, is observed on a single collision basis by monitoring changes in the vibrational level populations of propynal as reflected in the laser excitation spectrum. It is concluded that vibration → vibration processes account for these observations and occur only with collision partners for which near resonant pathways exist. Under even the most favorable conditions (ΔE=40 cm−1), neither vibration → translation pathways nor multiple quantum changes involving nondriven modes are observed when ν6 is the pumped mode. Observations suggest that multiple quantum events involving the pumped mode occur, but comparison of rate constants from different levels is hindered at present by the identification of overtones in the visible spectroscopy.

Potential curves for the ground and excited states of the NaN 2 system

The potential curves for the ground and excited states of the NaN 2 system are calculated in C ∞v, C 2v, C S-symmetry, using a modified HF-method. The results explain the quenching and excitation of Na atoms colliding with N 2 molecules observed in scattering experiments, with particular reference to the population of the final vibrational levels in N 2, and to the possibility of rotational excitation.

Electronic excitation in reactive collisions of Cs atoms with nonmetal fluorides

Whereas the reaction of Cs with SF 6 and several other halide molecules proceeds via a long-lived complex (Cs + XF n å [CsF—XF n − 1 ] å CsF + XF n −1 ) and results in a statistical energy distribution of the products, the population of the lower vibrational levels of CsF obtained from Cs + SF 4 or IF 5 is surprisingly high. Simple MO-arguments show the possible existence of low-lying electronic states in the reaction complex. From soft X-ray absorption spectra of TeF 4 we deduce that the energy of the IF 5-reaction is sufficient to populate the lowest excited electronic state of the product radical IF 4. SCF-calculations on SF 3 show that the potential hypersurfaces of the lowest three electronic states are Jahn—Teller-like connected, so that one expects strong electronic transitions in the complex due to vibronic coupling. The branching ratio to ground state and electronically excited products is dynamically determined notwithstanding the statistical vibrational distributions.

Vibrational level populations in the autoionization of oxygen

Autoionization from the I and I′ resonance series of O2 has been reexamined using high resolution for photons and electrons. Photoelectron spectra on the resonances are predicted from the upper potential energy surface parameters and photoionization yield curve alone, without reference to the uncertain line shapes and widths. Bond lengths are determined as 1.370±.005 Å in I and 1.380±.005 Å in I′ of O2.

Collisional deactivation of selectively excited N+2

Individual vibrational levels of the A 2Πu state of the N+2 molecular ion are excited by a tunable dye laser. Detection of an optical–optical double resonance fluorescence signal produced by a second laser demonstrates that the ions originally pumped into the A 2Πu state are rapidly deactivated by collisions with He into high vibrational levels of the ground X 2Σ+g state. Time and wavelength resolved studies show clearly that the population of a given high vibrational level of the X 2Σ+g state returns into lower A 2Πu state levels giving rise, effectively, to vibrational relaxation within the A state. Rate constants and cross sections are derived for these collisional, internal-conversion processes. In homonuclear N+2, where symmetry considerations prohibit X and A state perturbations, these processes proceed as rapidly as in heteronuclear species where perturbations are known to be present in the free molecule.

Collision-induced energy absorption and vibrational excitation by intense laser radiation in CH3F

Vibrational energy absorption and transfer in diatomic and polyatomic molecules from intense resonant laser pulses is studied in the regime where energy flow is determined by vibrational–vibrational (V–V) collisions. Simple theoretical models for single mode (diatomic) and two mode (polyatomic) oscillators, based on coupled rate equations with the addition of a laser pumping term, are presented. By invoking quasiequilibrium (temperature) assumptions on the vibrational level populations (confirmed with computer simulations) simple expressions are derived for the absorbed energy in the single mode case; and for two modes similar formulas based on a two-temperature model are derived and discussed in relation to the one mode model. For many cases of interest, CH3F included, the influence of a second mode on the total energy absorption is insignificant, with most of the energy flowing into the mode being pumped at nearly the same rate as for a single mode oscillator. The experimental work studies the absorption of the P(32) line of CO2 by 13CH3F, and the subsequent energy transfer among the several modes of the molecule. Approximately 1/4 J over 2 to 3 μsec delivers several quanta per molecule to the vibrational degrees of dreedom. Fitting the theoretical model to the measured absorption produces a V–V rate constant of γVV =1.0±0.5 μsec−1 Torr−1 for the ν3 mode. A determination of the energy partitioning among the several modes, by means of a technique for measuring the absolute energy stored in each, shows that roughly 50% of the absorbed energy is stored in the ν3 vibration with the remainder distributed among the other modes. Detailed knowledge of the partitioning allows confirmation of a specific energy flow path for CH3F.

Projectile, parent molecule and collision environment dependence of the dissociative excitation of CH A2Delta -X2Pi

A low resolution survey comparison of the population distribution of the CH A2 Delta -X2 Pi system formed by the dissociative excitation of acetylene, acetone and butane by the impact of 21 keV Kr+ and of butane by 43 keV Ne+ ion bombardment is reported. Little sensitivity of the rotational level population distribution to the target molecule from which the radical was ejected, or to the environment or the latter-whether gas phase, or adsorbate layer on a silicon substrate, or solid (frozen)-was observed. Apparent non-equilibrium of the rotational level distribution in the (0,0) band for 21 keV Kr+ ion induced dissociation contrasts with the equilibrium-like distribution for 43 keV Ne+ bombardment, despite only a factor of three increase in projectile velocity. A particular sensitivity of the rotational level excitation mechanism to the electronic structure of the projectile is suggested, rather than to the collision time, or molecule, or molecular environment from which the radical was derived. The vibrational level population distribution is found to exhibit a strong parent molecule and environment dependence.

Non-Boltzmann, non-Treanor vibrational level populations of electrical discharge excited nitrogen

Vibrational level population distributions of electrical discharge excited nitrogen were measured to v=5 using the electron beam fluorescence diagnostic technique. Measurements were made in the free jet expansion from an electrical discharge for both pure nitrogen and nitrogen–carbon monoxide mixtures. All measured distributions were highly non-Boltzmann and also deviated from the Treanor quasisteady state distribution. A numerical matching technique was used to predict the shape of the vibrational population distribution for a given total vibrational population. The numerical results predict the shape of the distribution very well for all experimental conditions. The numerical modeling also showed that the deviation from Treanor conditions occurs because the V–V rates and electron excitation rates in the discharge are of the same order of magnitude for discharge pressures of a few Torr.

IR multiple photon dissociation of fluorinated ethanes and ethylenes: HF vibrational energy distributions

The IR multiple photon dissociation of fluorinated ethanes and ethylenes produces vibrationally excited HF via collisionless molecular elimination. The HF† fluorescence spectra have been measured and analyzed in order to determine the relative vibrational level populations produced by the dissociation processes. These results are compared to those obtained by others who used alternate methods of excitation. The measured vibrational level distributions cannot be adequately represented by single temperature Boltzmann distributions or by a statistical partitioning of the available energy. It is estimated that less than 30% of the fixed energy appears as vibrational excitation of the HF fragment.

Sub-Doppler laser spectroscopy of the NaK molecule

Excitation of NaK molecules in a collimated molecular beam by a single mode tunable argon laser with sub-Doppler resolution allows selective population of definite vibrational rotational levels (v′, J′) in the D 1Π-state. The resultant fluorescence consists of a singlet spectrum in the 470–570 nm range and a triplet spectrum in the 625–715 nm range. The analysis of the triplet fluorescence, which consists of discrete lines and of a modulated continuum, allows the determination of the a 3Σ+ potential and yields very precise values for the dissociation energies in the a 3Σ+ and X 1Σ+ states, which are measured as De(3Σ+) =204±4 cm−1 and De(1Σ+) =5269±6 cm−1. For some excitation wavelengths a fluorescence spectrum with discrete lines and with a double-modulated continuum is observed which is assigned to ’’ Condon internal diffraction’’ bands terminating close below and above the dissociation limit of the X 1Σ+ state. Its relevance for the determination of the upper and lower potential curves is discussed.

EPR study of Cd(I) and Hg(I) hot ions: Effect of surrounding lattice

Hot ions Cd(I), and Hg(I), which are produced in lattices K 2[Zn(CN) 4], K 2[Cd(CN) 4], and K 2[Hg(CN) 4], have been studied by EPR. The distortion of crystal field from tetrahedral is classified into two types, one occurring along the metal-ligand bond and the other along the bisector of metal-ligand bond angles; Cd(I) formed in K 2[Cd(CN) 4] at 77 K belongs to the former and Cd(I) in K 2[Zn(CN) 4] to the latter. The number of sites for Hg(I) is different between two phases of K 2[Hg(CN) 4]. In Hg(I) complexes produced at 77 K, the degree of distortion increases with the increase of lattice size. Slight distortion is observed in the primary species Cd(I), and Hg(I), produced at 4.2 K. Temperature dependence of the hyperfine interaction observed in species produced at 77 K is attributed to a decrease of the axial field which is caused by thermal population of vibrational levels. Reorientation among three sites has been observed in Cd(I) formed in K 2[Zn(CN) 4].

Influence of second kind collisions on the electron distribution function in the positive column of low pressure nitrogen discharge

A numerical solution of the Boltzmann equation for the electron gas in the positive column of a DC discharge in nitrogen is presented. The Boltzmann equation was solved with the inclusion of the second kind (superelastic) collisions proceeding from the first six excited vibrational levels of molecular nitrogen. The vibrational level population is supposed to follow a Boltzmann distribution for a given vibrational temperatureT v, with a possible deviation of the ground level, which can be overpopulated in a given ratioγ. Apart from the electron distribution functions, which were gained for various values ofE/p 0,T v andγ, the values of some production frequencies and kinetic coefficients are presented in form of tables and plots. It is found that the electron distribution (and also the corresponding production rates) depends above a certain energy limit onT v andγ through the normalization constant only.

INTERACTIONS OF SWIFT H, H+2 AND H+3 WITH THIN FOILS

INTERACTIONS OF SWIFT H, H⁺₂ AND H⁺₃ WITH THIN FOILS

Conformations and temperature variation of the dipole moments of the alkoxy- and alkylthioethenes and their heteroorganic analogs

1. The alkoxy- and alkylthioethenes with normal radicals and Me groups exist predominantly in the s-cis conformation; the fact that their dipole moments increase with rising temperature is due to an increase in the fraction of molecules in the energetically favored, more polar, gauche form. 2. The alkoxy- and alkylthioethenes with tertiary radicals exist in the single gauche conformation. The fact that the dipole moments of these compounds decrease with rising temperature is due to an increase of the population of the upper torsional vibrational levels for rotation relative to the\(C_{sp^2 } - X (X = O, S)\) bond with approach to the less polar s-trans structure. 3. The lack of a temperature variation in the dipole moments in the Me3ESCH = CH2 vinyl sulfides is due to the fact that the polarity is only weakly dependent on the angle of rotation in the E-S-C=C system.

Energy characteristics of a carbon monoxide gasdynamic laser

The characteristics of gasdynamic lasers based on mixtures of carbon monoxide with nitrogen and inert gases were investigated and the populations of vibrational levels of CO molecules, the gain of the mixture, and the generation power were determined in [1–8]. But the parameters of a gasdynamic laser (GDL) in the optimum emission mode have not been determined up to now. The difficulties in calculating the optimum energy characteristics are connected with the complexity of the calculating model and the large number of parameters of the system. The energy characteristics of a CO gasdynamic laser are calculated and optimized in the present report on the basis of a simple model.

IR spectroscopic determination of the vibrational level populations of CO2 molecules in gasdynamic lasers

IR spectroscopic determination of the vibrational level populations of CO2 molecules in gasdynamic lasers

Chemiluminescence studies of boron atom reactions with O 2 and N 2O

The reactions of boron with O 2 and N 2O have been studied in a beam-gas experiment. Chemiluminescence is detected only from the B + O 2 reaction for which the total chemiluminescent cross section is estimated to be 0.05 A 2. Relative populations of vibrational levels and cross sections for their formation have also been obtained.

The OH Meinel bands in the airglow—the radiative lifetime

A model of the rotational relaxation of an emitting population has been used to determine the rotational temperature of emitted spectra for the OH Meinel bands. It is shown that the calculated rotational temperatures for these spectra are consistent with laboratory observations of the hydrogen–ozone reaction if the radiative lifetime for the Meinel bands is short, [Formula: see text]The model is also used to infer the initial rotational populations of the OH vibrational levels excited in the hydrogen–ozone reaction. It has been found that these initial rotational populations may be described by rotational temperatures of 1940, 1230, and 760 K for the seventh, eighth, and ninth vibrational levels, respectively. It is also concluded that the rate constants for vibrational quenching will be increased from previously accepted values. The effect of a short radiative lifetime for airglow observations is also discussed.