R.K. Khanna

Studies of proton-irradiated cometary-type ice mixtures

Abstract Radiation synthesis has been proposed as a mechanism for changing the nature of the outer few meters of ice in a comet stored 4.6 billion years in the Oort cloud and may explain some of the differences observed between new and more evolved comets. Cometary-type ice mixtures were studied in a laboratory experiment designed to approximately simulate the expected temperature, pressure, and radiation environment of the interstellar Oort cloud region. The 2.5- to 15-μm infrared absorption features of thin ice films were analyzed near 20°K before and after 1 MeV proton irradiation. Various ice mixtures included the molecules H 2 O, NH 3 , CH 4 , N 2 , C 3 H 8 , CO, and CO 2 . All experiments confirm the synthesis of new molecular species in solid phase mixtures at 20°K. The synthesized molecules, identified by their infrared signatures, are C 2 H 6 , CO 2 , CO, N 2 O, NO, and CH 4 (weak). Synthesized molecules, identified by gas chromatographic (GC) analysis of the volatile fraction of the warmed irradiated ice mixture, are C 2 H 4 or C 2 H 6 , and C 3 H 8 . When CH 4 is present in the irradiated ice mixture, long-chained volatile hydrocarbons and CO 2 are synthesized along with high-molecular-weight carbon compounds present in the room temperature residue. Irradiated mixtures containing CO and H 2 O synthesize CO 2 and those CO 2 and H 2 O synthesize CO. Due to radiation synthesis, ∼1% of the ice was converted into a nonvolatile residue containing complicated carbon compounds not present in blank samples. These results suggest that irrespective of the composition of newly accreted comets, initial molecular abundances can be altered and new species created as a result of radiation synthesis. Irradiated mixtures exhibited thermoluminescence and pressure enhancements during warming; these phenomena suggest irradiation synthesis of reactive species. Ourbursts in new comets resulting from similar radiation induced exothermic activity would be expected to occur beginning at distances of the order of 100 AU.

Infrared and mass spectral studies of proton irradiated H2O + CO2 ice: Evidence for carbonic acid☆

Abstract The effects of proton irradiation on mixed H2O + CO2 (1:1) ices at 20 K were investigated by infrared and mass spectroscopy. Infrared bands due to several radical (HCO, CO3) and molecular (CO) product species were identified. In addition, several new broad and complex i.r. features were observed. On slow warming, the broad features evolved into a 215–250 K residual film whose absorptions have been tentatively assigned to carbonic acid. This identification agrees with the spectral data for irradiated H2O + 13CO2 ice and the results of an approximate normal coordinate analysis.

Studies of proton irradiated H2O + CO2 and H2O + CO ices and analysis of synthesized molecules

Infrared spectra of H2O + CO2 and H2O + CO ices before and after proton irradiation showed that a major reaction in both mixtures was the interconversion of CO2 ⇌ CO. Radiation synthesized organic compounds such as carbonic acid were identified in the H2O + CO2 ice. Different chemical pathways dominate in the H2O + CO ice in which formaldehyde, methanol, ethanol, and methane were identified. Sublimed material was also analyzed using a mass spectrometer. Implications of these results are discussed in reference to comets.

Carbamic acid: molecular structure and IR spectra

Infrared absorption spectra of mixed H2O, NH3 and 12CO2/13CO2 ices subjected to 1 MeV proton irradiation were investigated. The results of analyses of the spectra suggest formation of carbamic acid at low temperatures. The stability of this compound in the solid phase is attributed to intermolecular hydrogen bonding of the zwitter-ion (NH3+ COO-) structure.

Vibrational infrared and raman spectra of dicyanoacetylene

The raman and infrared spectra for solid C4N2 are reported. New assignments are given for \gn1 (2333 cm−1), \gn2 (2267) and \gn3 (640 cm−1). These assignments are supported by a normal coordinate Analysis using eight force constants. Extinction coefficients for the infrared active fundamentals are also reported. Our results suggest C4N2 to be a likely candidate to explain the 478 cm−1 band in the Titans emission recorded by the Voyager mission.

Infrared spectrum of solid isocyanic acid (HNCO): vibrational assignments and integrated band intensities.

Infrared spectra of thin films of solid HNCO condensed from the gas phase are characterized in terms of their vibrational frequencies, mode assignments, and integrated band intensities at low temperatures ( approximately 20-145 K). Isocyanic acid is shown to react with water (H2O) and ammonia (NH3) even at low temperatures; consequently, it may be an important species in the chemistry of interstellar ices and comets.

Infrared spectra of some scheelite structures

Abstract The infrared spectra of powdered samples of CaWO 4 , CaMoO 4 , PbWO 4 and PbMoO 4 have been recorded from 1000 to 60 cm −1 . The spectra of thin single crystal plates of these specimens have also been recorded from 2000 to 1000 cm −1 . All the infrared active fundamental modes have been assigned. Similarities and differences between the infrared and the previously reported Raman spectra are discussed in the light of intermolecular coupling between the modes and the frequency dependence upon the phonon wave vector.

Resonance Raman spectra and vibrational assignments of Azulene-d0 and Azulene-d8☆

Abstract The observed resonance effects in the Raman spectra of Azulene (C 10 H 8 ) and its completely deuterated analog are utilized to assign the totally symmetric modes of these molecules. In conjunction with the data on the i.r. spectra and the normal coordinate analysis a complete assignment of the vibrational modes of these molecules is presented. The experimental excitation profiles are analyzed in the light of some current theoretical approaches. The experimental data strongly suggest that the variation of transition moment with the vibrational coordinate gives a dominant factor in determining the resonance Raman intensity of a mode.

Absorption intensities and complex refractive indices of crystalline HCN, HC3N, and C4N2 in the infrared region

Absorption intensities of thin crystalline films of HCN, HC3N, and C4N2 are given in the infrared region (4000-45;0 cm−1). The transmission spectra were corrected for scattering and inhomogeneity within the films. The complex refractive indices, n and k, were determined using a program that performs iterations of the Kramers-Kronig integral by utilizing a point-by-point least-squares fitting of the experimental transmission data. Transmission spectra generated using these n and k values reproduce the experimentally observed transmission data to within ±2%.

Absorption and resonance Raman spectra of Pb2, Pb3, and Pb4 in xenon matrices

Lead metal was vaporized and trapped in solid xenon at 12 K. Electronic absorption and resonance Raman spectra were recorded of the resulting matrix, which was shown to contain Pb2, Pb3, and possibly Pb4 molecular species. The vibrational frequency for Pb2 is determined to be 108 cm−1 for the ground state, with a dissociation energy of ∼8200 cm−1. A D3h symmetry is suggested for the Pb3 species, with ν1=117 and ν2=96 cm−1. The existence of Pb4 is suggested by a fundamental and overtone of 111 cm−1 spacing.