H. P. Broida

Rotational, Vibrational, and Electronic Energy Transfer in the Fluorescence of Nitric Oxide

A sharp emission line of ionized cadmium from an electric discharge excites NO molecules to the K′=13 rotational level of the v′=1 vibrational level of the A 2Σ+ electronic state. Steady‐state fluorescence has been observed from this level and from neighboring levels populated by collisional interaction between the excited and added inert molecules. Cross sections have been measured in He, Ar, H2, N2, NO, and CO2 for electronic deactivation to the ground X2II state, for vibrational deactivation to the v′=0 level of the A 2Σ+ state, and for rotational exchange in the A 2Σ+ state. It has been established that rotational transitions having changes in rotational quantum number greater than unity take place with high probability, contrary to the optical selection rule.

Chemical and Magnetic Enhancement of Perturbed Lines in the Violet Spectrum of CN

A chemical kinetic theory based on the quantum‐mechanical properties of perturbed molecular states is developed to explain the rotational intensity anomalies observed in the CN‐band spectrum emitted by an active nitrogen flame. Relative intensities of perturbed lines are calculated in terms of parameters which specify the rates of chemical formation, collisional relaxation, and radiative decay of CN molecules in the excited electronic states where the perturbed lines originate. Numerical values of these parameters are found which, inserted in the intensity expressions, predict correctly the observed pressure‐dependent enhancement of each perturbed line. From this analysis the approximate value 6×10—7 sec is found for the radiative lifetime of the A2IIi, v′=10 state of CN. It is also found that nearly every gas kinetic collision changes the rotational state of an excited CN molecule, but that only about 1 collision in 100 can cause the exchange of vibrational energy for electronic energy represented by the...

Spectra Emitted from Solid Nitrogen Condensed at Very Low Temperatures from a Gas Discharge

Solid products from electrical discharges containing nitrogen emit visible light at temperatures below 40°K. The observed spectra depend greatly upon (1) the temperature at which the discharge products are condensed, (2) the rate of deposition of the gas, (3) the addition of small amounts of impurities, and (4) the addition of large amounts of inert gases. A detailed survey of the effect of these parameters is presented, in order to understand better the mechanisms responsible for the various types of radiation which are observed.

Chemically Induced Vibrational Excitation: Hydroxyl Radical Emission in the 1–3 Micron Region Produced by the H+O3 Atomic Flame

A detailed investigation has been performed in the 1‐ to 3‐μ wavelength region on the radiation emitted by the hydroxyl radical from a low‐pressure flame of ozonized oxygen and atomized hydrogen. Wavelengths and photon intensities have been obtained for about 300 lines in the OH vibration‐rotation bands V—V—ΔV where ΔV=3, V=9 to 5, and for ΔV=2, V=9 to 2. Relative photon band intensities have been determined from the overdetermined set of data by a method of successive approximations using an IBM 650 computer. Dipole moment parameters have been calculated using the above data and Morse oscillator transition probabilities.Approximate rotational and vibrational Boltzmann distributions exist with an average rotational ``temperature of 560°K for the P branches, 460°K for the R and Q branches, and a vibrational ``temperature of 9250°K for the ΔV=2 and 3 bands. The absence of radiation from levels V>9 confirms the nonthermal character of the excitation and its dependence on the energetics of the reaction O3...

Emission Spectra of N2, O2, and NO Molecules Trapped in Solid Matrices

Molecular systems are observed in emission in solid products from a gas discharge trapped at liquid helium temperature. Previous tentative molecular assignments have been checked with the help of isotopic substitutions of oxygen and nitrogen. The Herzberg system (A bands) of oxygen (A 3Σu+ — X 3Σg—) is analyzed and the molecular constants are derived for a molecule trapped in a nitrogen matrix. Another system (M bands) is attributed to the NO molecule (4II — X 2II).

Measurements of Collisional Energy Transfer between Rotational Energy Levels in CN

A microwave‐optical technique which selectively populates a single rotational level of CN and permits the observation of the redistribution of this population was utilized to measure the rates of collisional energy transfer between rotational energy levels of the B2Σ state of CN. CN was formed in the A 2Π state by the addition of CH2Cl2 to the afterglow of a nitrogen discharge. The near coincidence of the K=4, v=10 level of the A 2Π state with the K=4, v=0 level of the B 2Σ state permits microwave transitions near 10 GHz from the more populated Π level to the Σ level. The increased population in the rotational levels neighboring the K=4 level of the B 2Σ state was detected by measuring the increased optical emission due to the B 2Σ—A 2Σ transition near 3875 A. Collisional energy transfer was measured over a pressure range from 0.1 to 5 Torr for changes in rotational quantum number ranging from one to ten. It is shown that rotational transitions having changes in rotational quantum number greater than unit...

Spectra Emitted from Rare Gas‐Oxygen Solids during Electron Bombardment

Light emission from rare gas solids containing small amounts of oxygen has been excited by an electron bombardment technique. The Herzberg bands of oxygen and a line group believed to be the 1S→1D transition of the neutral oxygen atom form the strongest features of the observed spectra. In a neon matrix, the Second Negative system of O2+ has been identified. The effect of the various solids on the vibrational structure of the Herzberg bands is discussed.

Spectral Study of a Visible, Short‐Duration Afterglow in Nitrogen

In the discharge products of rapidly flowing, pure nitrogen at pressures between 4 and 15 mm Hg, an afterglow differing from the usual Lewis‐Rayleigh afterglow has been found to occur approximately 5 milliseconds after the discharge. This pink‐colored afterglow persists for about 2 milliseconds and is both preceded and followed by the usual yellow glow of active nitrogen. In the visible and near ultraviolet, this short‐duration glow is characterized by strong emission of N2+u2009(Bu20092Σu+−X 2Σg+) and N2 1st positive (B 3Πg−A 3Σu+) bands and weak emission of N2 2nd positive (C 3IIu—B 3IIg) bands. The vibrational intensity distributions of the bands are similar to that of the discharge, including strong emission from vibrational levels above the predissociation limit of the B 3IIg state. The existence of this afterglow shows the presence of highly energetic species other than nitrogen atoms after the discharge.

Kinetics of OH Radicals from Flame Emission Spectra. IV. A Study of the Hydrogen‐Oxygen Flame

The inner cone of the acetylene‐oxygen flame burning lean (1:5), stoichiometric (2:5), and rich (4:5) at atmospheric pressure has been studied spectroscopically with the object of gaining some information about the elementary processes occurring in this flame. The rotational, vibrational, and electronic distributions of OH(2Σ+) have been determined for each fuel mixture. The analysis of the data showed a rotational Maxwell‐Boltzmann distribution with a rotational ``temperature several hundred degrees higher than the adiabatic flame temperature. The vibrational distribution of OH(2Σ+) was distinctly nonequilibrium with an excess population in the level v′=3 analogous to that observed for the hydrogen‐oxygen flame. This is attributed to the interaction of the 2Σ+ and 2Σ− states of OH. The analysis of the electronic distribution of OH indicated that OH(2Σ+) is present in its thermal equilibrium concentration in the flame at atmospheric pressure. The results of this study in conjunction with the work of Gay...

Effect of Molecular Oxygen on the Emission Spectra of Atomic Oxygen‐Acetylene Flames

Studies have been made of the emission spectra (3000 to 6000 A) obtained from low‐pressure atomic oxygen‐acetylene flames diluted with varying amounts of molecular oxygen and molecular nitrogen. Added molecular oxygen greatly increased the OH emission while reducing CH and C2 emission. It also had an effect on the rotational intensity distribution of OH and on the vibrational intensity distribution of C2. Nitrogen addition greatly reduced the rotational and vibrational ``temperatures and decreased C2 emission relative to the other emitters.