Daniel Forney

ELECTRONIC ABSORPTION SPECTRA OF LINEAR CARBON CHAINS IN NEON MATRICES. III. HC2N+1H

Absorption spectra observed between 400 and 2500 nm in 5 K neon matrices have been assigned to electronic transitions of linear C−2n (n=2–10): 2Π←X 2Π, C2n (n=3–7): 3Σ−u←X 3Σ−g, and C2nH (n=3–8): 2Π←X 2Π chains. The species have been produced by mass selected deposition of cations or anions produced in a hot cathode discharge source (C2n, C−2n, C2nH) and by laser vaporization of graphite (C2n, C−2n). In addition to experimental and chemical evidence, the dependence of the absorption wavelength on the number of carbon atoms was used to assign the electronic transitions. Infrared absorptions which were recorded around 2000 cm−1 are attributed to asymmetric stretching frequencies of C8, C10, and C12. This is based on correlation of their intensities with the identified electronic bands. The possible relevance of the electronic spectra of these carbon chains to astrophysical observations of diffuse interstellar bands is discussed.

The vibrational spectra of molecular ions isolated in solid neon. IX. HCN+, HNC+, and CN−

When a Ne:HCN sample is codeposited at ∼5 K with a beam of neon atoms that have been excited in a microwave discharge, infrared absorptions of HNC, HCN+, and CN− appear. The absorptions of HNC isolated in solid neon are considerably closer to the gas‐phase band centers than are the previously reported argon‐matrix absorptions. The CH‐stretching fundamental of HCN+ is identified, and the two stretching force constants of HCN+ are determined, using the isotopic data obtained in this study and the CN‐stretching frequencies of HCN+ and DCN+ obtained in earlier photoelectron spectroscopic studies. In the inert, nonpolar environment provided by the neon matrix, the infrared absorption of CN− appears at 2053.1 cm−1, very close to the position obtained in two recent ab initio calculations. HCN+ photoisomerizes to HNC+ with a threshold in the near‐infrared spectral region, consistent with an earlier ab initio calculation of the position of the transition state for this process. The reverse photoisomerization has a...

The vibrational spectra of molecular ions isolated in solid neon. XI. NO+2, NO−2, and NO−3

When a Ne:NO2 or a Ne:NO:O2 sample is codeposited at approximately 5 K with a beam of neon atoms that have been excited in a microwave discharge, infrared absorptions of NO+2, NO−2, and NO−3 appear. Detailed isotopic substitution studies support the assignment of prominent absorptions to ν3 of NO+2 and NO−2 and of weak to moderately intense absorptions to the ν1+ν3 combination band of each of these species. When the contribution of anharmonicity is considered, the positions of the NO+2 absorptions are in satisfactory agreement with the values for the stretching fundamentals obtained in a recent gas‐phase study of that species. When the sample is exposed to 240–420 nm mercury‐arc radiation, the initially present absorptions of NO−3 trapped in sites with a small residual cation interaction diminish in intensity, and the unsplit ν3(e’) absorption of isolated NO−3 grows. The mechanism responsible for this growth in the absorption of isolated NO−3 is considered.

Infrared Spectra of trans-HOCO, HCOOH+, and HCO2- Trapped in Solid Neon

When a Ne:HCOOH sample is codeposited at ca. 5 K with neon atoms that have been passed through a microwave discharge, new absorptions appear in the infrared spectrum of the resulting solid that can be assigned to trans-HOCO, trans-HCOOH+, and HCO2−. The absorptions of trans-HOCO are readily identified by a comparison with those previously reported for that molecule trapped in solid argon. Preliminary assignments of infrared absorptions of HOCO+, confirmed in studies using another experimental system, are also suggested. The identifications of trans-HCOOH+ and of HCO2− are aided by study of the photodestruction characteristics of these products when the deposit is exposed to various wavelengths of visible and ultraviolet radiation, by an analysis of the spectra obtained from isotopically substituted samples, and by a comparison with the results of ab initio and density functional calculations. Three previously unidentified vibrational fundamentals of trans-HCOOH+ have been assigned, as have been four vibra...

The vibrational spectra of molecular ions isolated in solid neon. X. H2O+, HDO+, and D2O+

When a Ne:H2O≥200 sample is codeposited at approximately 5 K with a beam of neon atoms that have been excited in a microwave discharge, new infrared absorptions appear close to the gas‐phase band centers of the three vibrational fundamentals of H2O+. Detailed isotopic substitution studies confirm this assignment and provide assignments for all of the vibrational fundamentals of HDO+ and D2O+. When ions are present in the neon matrix, rotation of a significant fraction of the water molecules is inhibited. Electrons produced by the photodetachment of anions, which must be present to maintain overall charge neutrality of the deposit, accelerate nuclear spin equilibration of water in the matrix. As the concentration of H2O+ is decreased by capture of the photodetached electrons, the absorptions assigned to nonrotating water are also reduced in intensity. The nature of the other ionic species which may be present in the sample is considered.

Infrared bands of mass-selected carbon chains Cn (n = 8−12) and Cn− (n = 5−10, 12) in neon matrices

Abstract Infrared bands of carbin chains C n ( n = 8−12) and C − ( n = 5−10, 12) have been observed in neon matrices in the 1600–2100 cm −1 region. The matrices were grown at 5 K by codepositing mass-selected carbon anions with excess of neon. The neutral carbon chains were obtained from the anions by photodetachment. The assignments of the infrared transitions are based on mass-selection, photobleaching behaviour, intensity correlation with the known electronic transitions, and available ab initio calculations.

Absorption spectroscopy of mass‐selected ions in neon matrices

A new approach for the spectroscopic characterization of mass‐selected ions is demonstrated. In this a stream of ions coming from a quadrupole mass selector are codeposited with neon to form a 5 K matrix and the absorption spectrum is measured. The potential of this technique is illustrated by the observation of the electronic absorption spectra of C+2, C2N+2, and C2Cl+2, in turn, after mass selection.

Electronic absorption spectra of cyano‐substituted polyacetylene cations in neon matrices

The A 2Π←X 2Π transitions and vibrational frequencies in the excited electronic states have been determined for the cyanopolyacetylene cations H–(C≡C)n–CN+ (n=2–6) and NC–(C≡C)n–CN+ (n=1–5). The spectroscopic information was derived by absorption measurements after cations from a mass selected beam were condensed together with excess of neon to form a 5 K matrix. Spectra have been also obtained for ions with odd number of π‐centers and are tentatively assigned to H–C2n−1–CN+ (n=3–6) and NC–C2n−1–CN+ (n=3–5). The assignments are based on trends observed for the homologous series of these cations, known gas phase data on three of the smaller species, and the free electron molecular orbital model.

Matrix isolation study of the interaction of excited neon atoms with CF4. Infrared spectra of CF+3 and CF−3

When a Ne:CF4 sample is codeposited at approximately 5 K with a beam of neon atoms that have been excited in a microwave discharge, the infrared spectrum of the resulting sample shows prominent absorptions of CF2 and CF3, as well as a complex absorption pattern between 1650 and 1670 cm−1. Earlier reports of the infrared spectrum of CF+3 produced from various CF3X species and trapped in solid argon are consistent with the assignment of this group of absorptions to ν3 of CF+3. The prediction of those studies that the ν1+ν4 combination band of 12CF+3 should lie near 1625 cm−1 is confirmed. Supplementary observations on Ne:HCF3 and Ne:DCF3 samples support these assignments, as well as that of the ν2(a2‘) fundamental of CF+3 at 798.1 cm−1. Ab initio calculations of the structure and vibrational fundamentals of ground‐state CF−3 are consistent with the tentative assignment of two infrared absorptions to that species.

The vibrational spectra of molecular ions isolated in solid neon. XVI. SO2+, SO2−, and (SO2)2−

When a Ne:SO2 mixture is subjected to Penning ionization and/or photoionization by neon atoms in their first excited states, between 16.6 and 16.85 eV, and the products are rapidly frozen at approximately 5 K, the infrared spectrum of the resulting deposit includes absorptions assigned with the aid of isotopic substitution studies to SO, SO2+, SO2−, (SO2)2−, and, tentatively, SO−. The fundamental and first overtone absorptions of SO lie 0.9 and 1.8 cm−1, respectively, below the gas-phase band centers. Ab initio calculations at the Hartree–Fock level show an instability in the v3 vibration of SO2+ which is avoided by higher-level calculations. The ν3 and ν1 fundamentals of SO2− isolated in solid neon are identified at 1086.2 and 990.8 cm−1, respectively. In agreement with an earlier proposal, the 1042 cm−1 absorption originally assigned to ν3 of SO2− trapped in solid argon is reassigned to MSO2, with M an alkali metal. Near the photodetachment threshold for SO2− isolated in a neon matrix, electron capture ...