R. L. Brooks

CARBON-CHAIN OXIDES IN PROTON-IRRADIATED CO ICE FILMS

After H2 and water, CO and CO2 are the most common molecules in stellar and interstellar environments. They are often dominant components in icy mantles of comets and interstellar dust grains. These ice mantles are subject to a varying degree of cosmic radiation, leading to chemical alterations. This paper presents a study of the near-IR absorption spectrum (1900–4000 cm � 1 ) of proton-irradiated CO thin films. The spectra of such films display several features arising in the vicinity of the CO fundamental that are attributed to carbon oxides such as Cn Oa nd CnO2 for n � 7. The formation mechanisms of carbon chains in interstellar environments are of interest since carbon chains (or molecules derived from them) have been considered to be carriers of some of the diffuse interstellar bands. Subject headingg astrochemistry — comets: general — dust, extinction — ISM: molecules — methods: laboratory

Electronic Structure of Diatomic Molecules

What makes the solution for the electronic motion in a molecule so much more difficult from that for an atom (which as we have seen is certainly not easy!) is that the problem, in general, is multicentered. In an atom, with a single nucleus, one may use spherical coordinates for the multielectron problem. The angular part of the problem is effectively solved by invoking spherical harmonics for the basis functions for each electron. In a molecule, spherical symmetry is broken, and one cannot even use the same quantum numbers that one could use for an atom. It is little wonder that most texts that do treat the quantum mechanics of molecules ignore the atomic underpinnings. One can hardly blame the authors; the methodology is fundamentally different.

Helium emission spectra from doped samples of solid hydrogen and deuterium

Using proton‐beam irradiation at 15 MeV, the emission spectra from 3He and 4He doped samples of solid hydrogen and deuterium have been observed from 350–750 nm at 4.2 K. Such samples simulate the conditions of solid tritium or tritiated hydrogens after about six days of helium accretion. The spectra are very similar to pure helium gas spectra acquired at 4.2 K and closer still to spectra acquired using helium gas in the upper portion of a sample cell partially filled with solid hydrogen. The helium collects as macroscopically large bubbles whose pressure has been determined. The pure 4He gas spectrum at 4.2 K contains a band near 460 nm previously assigned to an unspecified excimer–dimer radiative transition. The pressure and isotope dependence of this band is presented which lends support to that interpretation. A mechanism is proposed for the transition.

Helium hydride emission spectra at 550 and 640 nm

Emission spectra of three isotopomers of helium hydride (4HeH, 3HeH, and 3HeD) in the visible spectral region have been acquired using proton‐beam irradiation of dense helium gas (150 Torr) at 4.2 K in the presence of some solid hydrogen or deuterium. Besides the previously reported D 2Σ+→A 2Σ+ transition, near 550 nm, a second transition near 640 nm, identified as the D 2Σ+→B 2Π, has been acquired and analyzed. The spectroscopic constants for both transitions have been obtained and compared to the theoretical results based on the latest published potential curves. Further insight into the mechanism for forming HeH will be presented, which indicates that the formation process is sensitive to the hydrogen vapor pressure above the solid.

The UV‐visible emission spectra of oxygen and nitrogen in solid hydrogen and deuterium hosts

Spectra in the wavelength range of 300–600 nm have been acquired during proton‐beam irradiation of samples of solid hydrogen and deuterium at 4.2 K. Emission spectra from the transitions A′ 3Δu→X 3Σ−g of O2, 4S–2D of N i, and 1D–1S of O i have been measured and attributed to an air impurity in the sample. Comparison is made of the vibrational constants derived from the molecular bands, the spectral shifts of all features, and the lifetime of the 2p3 2D multiplet of N i obtained in the solid hydrogens with those obtained by matrix isolation studies using N2 and rare gas hosts.

Vibrational Spectrum and Analysis. Silver Azide Crystals

The vibrational spectrum (infrared, Raman, and far infrared) of silver azide crystals has been measured over the frequency range from 40 to 4000 cm−1. A factor‐group analysis was carried out for the classification and determination of selection rules of the k ≃ 0 vibrational modes of the crystals. Individual assignments are made for the modes due to lattice transitions, the multiplicity of fundamentals in the infrared and Raman, and for numerous combinations constituting fine structure in the medium infrared. Observed band structure of single‐crystal spectra are strongly influenced by crystal structure orientation with respect to the incident beam. Numerical checks are provided for the assignment of essentially all combinations and indirect determinations are made of the frequencies of several modes which are neither infrared nor Raman active. Discussion is made of observed absorptions which apparently are not governed by factor group selection rules. The over‐all observed spectrum is in general agreement...

Absorption spectra from high vibrational levels of He2

Absorption spectra of dense helium gas at cryogenic temperatures has been acquired while the sample was irradiated using a 6.5 MeV proton beam. By chopping the proton beam, rather than the source lamp, we were able to achieve one part in 104 spectral sensitivity. The spectra showed six new bands in 4He2 and three in 3He2. These have been identified as transitions between high‐lying vibrational levels, with the strongest originating on the highest bound level of the a 3Σ+u potential. The temperature and pressure dependence of these features, as compared to low‐lying molecular and atomic features, offers some insight into the reaction dynamics of this fundamental system.

Infrared emission spectra from cryogenic proton‐irradiated helium gas

Spectra from proton‐beam irradiated helium gas, near 4.2 K, have been examined in the near infrared spectral region using a sensitive photomultiplier‐grating spectrometer combination (750–1000 nm) and a Fourier transform infrared spectrometer with an InGaAs detector (800–1800 nm). Most of the observed features can be assigned to known He2 transitions, and two bands, not previously observed (d 3Σ+u(v=4)→c 3Σ+g(v=3,4)) have been identified and analyzed. Some of the unidentified spectra have qualitative similarity to a set of visible emission lines tentatively assigned to an excimer–dimer (i.e., He4, two He2 excimers weakly bound together). These features, unlike the normal He2 spectra, demonstrate pronounced dependence on both the pressure and temperature of the sample. A comparison of the intensities of the singlet and triplet D(d)→C(c) transitions to the singlet and triplet C(c)→A(a) transitions is made.

Photoionization of isoelectronic ions: Mg + and Al 2 +

High-resolution measurements of the photoionization cross sections of the Na-isoelectronic ions Mg{sup +} and Al{sup 2+} are presented, to be compared with earlier measurements in which structure in the most prominent peaks was unresolved. These measurements have been normalized to the earlier ones in order to provide values of the oscillator strengths of the newly resolved peaks, and comparison is made with multiconfiguration Hartree-Fock calculations.

Spectroscopic detection of the A(v=2) level of 4HeD

A new near infrared emission spectrum of 4HeD has been recorded at 4.2 K during proton irradiation of a mixed sample of helium gas and solid deuterium. The upper state of the transitions is an admixture of the accidentally degenerate D 2Σ+(v=0) and C 2Σ+(v=3) levels. The lower state is the previously unobserved A 2Σ+(v=2) level. The observation of this level allows for evaluation of the rotational constants B‘2 and D‘2 for the A 2Σ+ state, and for a better estimate of the vibrational parameters ω‘e and ω‘eχ‘e.