Marilyn E. Jacox

Spectroscopic Study of the Vacuum‐Ultraviolet Photolysis of Matrix‐Isolated HCN and Halogen Cyanides. Infrared Spectra of the Species CN and XNC

Vacuum‐ultraviolet photolysis of HCN isolated in Ar and N2 matrices at 14°K is found to lead to the production of HNC in concentration sufficient for direct infrared observation of all three vibrational fundamentals. The spectrum of this species is found to be appreciably perturbed by the presence of N2. The force constants and thermodynamic properties of HNC have been revised to the values appropriate to this species in an environment free of perturbation by an adjacent N2 molecule. The free radical CN is also produced in these systems in concentration sufficient for direct observation not only of the B(2Σ+)—X(2Σ+) transition but also of the ground‐state vibrational fundamental. Isotopic data supporting this identification are presented. Upon vacuum‐ultraviolet photolysis of matrix‐isolated FCN, two infrared absorptions appear which can be identified with the stretching fundamentals of the species FNC. In analogous experiments on the species ClCN and BrCN, infrared absorptions tentatively assigned to ClN...

Infrared and Ultraviolet Spectroscopic Study of the Products of the Vacuum‐Ultraviolet Photolysis of Methane in Ar and N2 Matrices. The Infrared Spectrum of the Free Radical CH3

The vacuum‐ultraviolet photolysis of methane in an argon or a nitrogen matrix at 14°K leads to the formation of a sufficient concentration of the methyl radical for observation both of its 1500‐A electronic transitions and of its out‐of‐plane deformation fundamental, which appears at 611 cm−1 for CH3 trapped in a nitrogen matrix. The value observed for this fundamental of CD3 is in reasonable agreement with the value previously derived from analysis of the 2160‐A band system. Isotopic substitution studies support the assignment of the 611‐cm−1 feature to ν2 of CH3. Data are consistent with the previous report of a planar structure. Evidence is presented suggesting that CH3 may rotate in an argon matrix. Although CH2 has not been directly observed, an appreciable concentration of CH2N2 appears in the N2 matrix experiments. Three electronic transitions of CH are observed in the argon matrix experiments, and there is evidence for the production of a small concentration of C atoms.

Vibrational and Electronic Energy Levels of Polyatomic Transient Molecules. Supplement B

A summary is presented of recently published, critically evaluated experimental vibrational and electronic energy level data for neutral and ionic transient molecules and high temperature species possessing from three to sixteen atoms. Although the emphasis is on species with lifetimes too short for study using conventional sampling techniques, there has been selective extension of the compilation to include data for isolated molecules of inorganic species such as the heavy-metal oxides, which are important in a wide variety of industrial chemical systems. Radiative lifetimes and the principal rotational constants are included. Observations in the gas phase, in molecular beams, and in rare-gas and diatomic molecule matrices are evaluated. The types of measurement surveyed include conventional and laser-based absorption and emission techniques, laser absorption with mass analysis, and photoelectron spectroscopy. Not counting isotopic species, 904 molecules are surveyed, and 2696 distinct references are given.

Matrix‐Isolation Study of the Reaction of Atomic and Molecular Fluorine with Carbon Atoms. The Infrared Spectra of Normal and 13C‐Substituted CF2 and CF3

Carbon atoms, resulting from the photolysis of cyanogen azide, are found to react with molecular fluorine in an argon matrix at 14°K to produce CF2. The use of carbon‐13 has led to confirmation of the previous assignment of features at 1073 and 1191 cm−1 to 13CF2 present in natural abundance. Using recent structural data on CF2 and the 12CF2 and 13CF2 frequencies, it has been possible to calculate the complete valence force potential of CF2. Values of the potential constants are compared with those of the related species NF2 and OF2. When the sample is subjected to radiation of wavelengths effective in photolyzing F2, CF3 is also produced. Sufficient yields of both 12CF3 and 13CF3 have been obtained for observation of all four vibrational fundamentals. Data have been fitted to a four‐constant valence force potential. Agreement is most satisfactory for a C3v structure with a deviation of 13° from planarity. Using this structure, the thermodynamic properties of CF3 have been estimated.

Matrix‐Isolation Study of the Infrared and Ultraviolet Spectra of the Free Radical HCO. The Hydrocarbon Flame Bands

The photoproduction of H or D atoms from a variety of sources in a carbon monoxide matrix or in an argon matrix to which a small concentration of carbon monoxide has been added leads to the appearance of prominent ultraviolet absorptions between 2100 and 2600 A, all of which may be assigned to HCO or DCO. Both the CO‐stretching and the bending vibrational modes are appreciably excited in the transition. Evidence is presented indicating that the transition observed in the matrix experiments is the same one responsible for the hydrocarbon flame bands. Using the frequencies observed in the matrix experiments, a tentative assignment for the hydrocarbon flame bands has been proposed which is in reasonable agreement with the observed band structure of the emission system. In the upper state, the carbon and oxygen atoms of HCO are approximately singly bonded. Observation of the infrared absorption frequencies of isotopically substituted HCO in an argon matrix has prompted reconsideration of the valence force field appropriate to ground‐state HCO. Interaction between the CH‐stretching and the CO‐stretching modes has been found to play an important role. Factors leading to the stabilization of HCO in an argon matrix in the present experiments, in contrast to the results of previous studies, are discussed.

Ground‐State Vibrational Energy Levels of Polyatomic Transient Molecules

The experimentally determined ground‐state vibrational energy levels of approximately 480 covalently bonded transient molecules possessing from 3 to 16 atoms are tabulated, together with references to the pertinent literature. The types of measurement surveyed include laser‐based high resolution gas phase infrared absorption and visible‐ultraviolet emission techniques, ultraviolet photoelectron spectroscopy, and matrix isolation spectroscopy. An assessment of the magnitude of the uncertainty of observations in neon, argon, and nitrogen matrices is given.

Vacuum‐Ultraviolet Photolysis of Acetylene in Inert Matrices. Spectroscopic Study of the Species C2

The vacuum‐ultraviolet photolysis of acetylene isolated in Ar, Ne, and N2 matrices at 4° and at 14°K is shown to lead to the appearance of a number of visible‐ultraviolet absorption bands which may be assigned to the species C2, as well as to an 1848 cm−1 infrared absorption assigned, with the aid of isotopic substitution studies, to the free radical HC2. The (0, 0) band of the Mulliken system of C2 is observed with great intensity at 2382 A (Ar matrix) or at 2323 A (Ne matrix) and the (2, 0), (3, 0), and (4, 0) bands of the Phillips system of C2 are observed in an Ar matrix at 8700, 7675, and 6880 A, respectively, indicating that the x 1Σg+ state of C2 is the ground state of this species not only in the gas phase but also in the matrix. Features assigned by previous workers to the Swan transition of triplet C2 appear at 5206 and 4725 A. A third member of the progression, not previously observed, appears at 4334 A. Experiments utilizing C2D2 and C2H2 (58% 13C) support the assignment of these features to C...

The à 2Π–X̃ 2Σ+ transition of HC2 isolated in solid argon

Fourier transform absorption spectra have been obtained between 700 and 7900 cm−1 at a resolution of 0.2 cm−1 for Ar:C2H2 samples codeposited at 12 K with a beam of argon atoms that had been excited in a microwave discharge. Detailed isotopic substitution studies have confirmed that the predominant product species is HC2, which contributes not only the absorptions previously assigned to its two stretching fundamentals but also several weaker absorptions in the 2000–3600 cm−1 spectral region and a prominent, complicated pattern of absorptions between 3600 and 7800 cm−1. The previous assignment of the 3611 cm−1 HC2 absorption as the CH‐stretching fundamental is reviewed, and the assignment of an absorption at 2104 cm−1 as ν2+ν3 of ground‐state HC2 is discussed. The near infrared absorption band system has been assigned to the A 2Π–X 2Σ+ transition of HC2, extensively perturbed by interaction with high vibrational levels of the ground state. The position of the transition origin could not be definitively e...

Infrared Spectrum and Structure of Intermediates in the Reaction of OH with CO

Upon vacuum‐ultraviolet photolysis of H2O in a CO matrix at 14°K, infrared absorptions of HCO, H2CO, HCOOH, and CO2 become prominent. Furthermore, new absorptions due to reactive product species appear at 615, 620, 1077, 1088, 1160, 1261, 1797, 1833, 3316, and 3456 cm−1. These absorptions diminish in intensity when the sample is subjected to radiation in the 2000–3000‐A spectral range. Detailed consideration of the processes which may occur in this system and extensive isotopic substitution studies support the assignment of these absorptions to the cis and trans stereoisomers of H–O–C=O, produced by the reaction of OH with the CO matrix. Valence force potentials having only small contributions from interaction terms have been found which correspond to a physically reasonable vibrational assignment and which satisfactorily reproduce the pattern of observed frequencies for the various isotopic species of both cis‐ and trans‐HOCO. Evidence suggests that cis‐ and trans‐HOCO photodecompose to produce H atoms and CO2.

Infrared Spectrum of HCO

HCO and DCO have been prepared by the photolysis of HI (DI) and of H2S (D2S) in a CO matrix at 14° and at 20°K. The earlier infrared spectroscopic identification of these species has been confirmed. The C=O stretching frequency of DCO has been revised to 1800 cm—1. Unusually low C–H and C—D stretching frequencies, 2488 and 1937 cm—1, respectively, are obtained. Observations on H13CO and D13CO support these assignments. Spectroscopic, kinetic, and electron spin resonance data all suggest that the C–H bond is exceptionally weak. Fermi resonance may occur between the C—D and C=O stretching modes of DCO. Evidence is presented suggesting that considerable activation energy is required for the reaction of H atoms with CO.