Catherine L. Lugez

Absolute intensities for the O2 1.27 μm continuum absorption

Collision-induced absorption coefficients for the 1.27 μm band of O2 have been measured at a resolution of 0.5 cm−1 and an optical path length of 84 m using a Fourier transform spectrometer. Spectra were recorded for sample densities ρ from 1 to 10 times that of an ideal gas under standard conditions (T = 273.15 K and P = 101.325 kPa) at temperatures of 253, 273, and 296 K for pure O2 and O2/N2 mixtures. After removing the contributions from the sharp lines of the υ = 0 ← 0 component of the O2 a1Δg ← X3∑g− band, which overlaps the continuum band, the integrated band strength per unit path length, S ≡ SO2−O2ρO22 + SO2−N2ρN2ρO2, has been determined for several values of the densities, ρO2 and ρN2, to give values for SO2−O2 and SO2−N2. At 296 K we find SO2−O2 = 4.847(22) × 10−43 cm−2 (molecule/cm3)−2 and SO2−N2 = 0.941(50) × 10−43 cm−2 (molecule/cm3)−2. Type A standard uncertainties are given, that is, ±1σ, from a least squares analysis of the integrated-intensity-versus-density data. The SO2−O2 coefficient is in reasonable agreement with the previous measurements of Cho et al. [1963]; however, our value for SO2−N2is 2.6 times greater than their results. Our derived air coefficient SO2−air is 37% greater than the atmospheric value of Mlawer et al. [1998], after correcting their continuum value for an updated value for the absorption coefficients for the overlapping discrete structure of the O2a1Δg ← X3∑g− band.

Experimental and ab initio study of the infrared spectra of ionic species derived from PF5, PF3, and F3PO and trapped in solid neon

When a Ne:PF5 or a Ne:PF3 mixture is codeposited at 5 K with a beam of neon atoms that have been excited in a microwave discharge, the infrared spectrum of the resulting solid shows a complicated pattern of new absorptions. Little fragmentation of PF5 into PF3 occurs, but several of the absorptions can be tentatively attributed to PF4. The results of extensive ab initio calculations of the vibrational spectra of the neutral, cation, and anion species of formula PFn are presented, in order to aid in the product identification. Several absorptions of PF4+, PF3+, and PF2+ are identified, with only PF3+ common to both systems. Other prominent absorptions are contributed by PF5−, PF4−, and PF3−. In all of the Ne:PF5 experiments and some of the Ne:PF3 experiments, F3PO was a major contaminant. Therefore, ab initio calculations were also conducted for most of the neutral and charged species that can result from F3PO. There is strong evidence supporting the identification of two of the vibrational fundamentals of...

Microwave studies of three alkylbenzenes: Ethyl, n-propyl, and n-butylbenzene

The rotational spectra of ethyl, n-propyl, and n-butylbenzene have been observed and analyzed using a high-resolution Fourier transform microwave spectrometer. Only one stable conformation was found for ethylbenzene, in agreement with previous results from Caminati et al. [Mol. Phys. 74, 885 (1991)]. The high sensitivity of the technique allows observation of the rotational spectra of the six 13C isotopes of ethylbenzene in natural abundance. The structural analysis indicates that the dihedral angle between the ethyl group and the ring plane is 88.7°±0.9°. Two conformers have been found for n-propylbenzene as predicted by ab initio calculations while four of the five theoretically predicted conformers [Dickinson et al., J. Chem. Soc., Faraday Trans. 93, 1467 (1997)] have been found for n-butylbenzene.

Rotational spectra of four of the five conformers of 1-pentene

The rotational spectra of four of the five expected conformers of 1-pentene, together with their monosubstituted 13C isotopic forms, have been measured in a molecular beam using a pulsed-nozzle Fourier-transform microwave spectrometer. One of the conformers has Cs point-group symmetry while the other three conformers have C1 point-group symmetry. The measurements are compared to results from molecular modeling calculations using the MM3 molecular-mechanics force field of Allinger et al. and to ab initio electronic structure calculations (MP2/6-31G*, MP2/6-311G*, MP4/6-31G*, MP4/6-311G*). Both types of calculations suggest the existence of five distinct conformers of 1-pentene, four of C1 symmetry and one of Cs symmetry. Both the MM3 and ab initio rotational constants deviate from the measured values by ⩽5%. The relatively high barriers between the four conformers limit the conformational cooling in the expansion, allowing all four conformers to be observed at the <2 K rotational temperature of the molecul...

Infrared spectra of (NO)2+, (NO)2−, and (NO)3− trapped in solid neon

New studies of the infrared spectra of the products which result on codeposition at approximately 5 K of a Ne:NO sample with Ne atoms that have been excited in a microwave discharge have led to new and revised assignments for several ionic species. The appearance of the ν1 absorption of ONNO+ for several new species with asymmetric isotopic substitution, but for no symmetrically substituted species, confirms the trans ground-state configuration for ONNO+. The behavior of a neon-matrix product absorption at 1227.5 cm−1 parallels that of an argon-matrix absorption at 1221.0 cm−1 which has recently been assigned to trans-ONNO−. The identity of the carrier of a product absorption at 1424.1 cm−1, contributed by a vibration of two symmetrically equivalent NO groups, has not been definitively established. This absorption exhibits complex photodestruction behavior. Three absorptions are assigned to cis,cis-(NO)3−, which has C2v symmetry, with the aid of density functional calculations of the isotopic substitution pattern for the vibrational fundamentals of this species. Similar calculations of the isotopic substitution patterns for other structures result in poor agreement with the experiments. Photodestruction of cis,cis-(NO)3− trapped in solid neon yields the N2O⋯NO2− complex.

The vibrational spectra of molecular ions isolated in solid neon. XIV. CH3F+, CH3Cl+, CH3Br+, and their ylidion isomers

When a Ne:CH3X (X=F, Cl, Br) sample is codeposited at approximately 5 K with neon atoms that have been excited in a microwave discharge, the infrared spectrum of the resulting solid deposit includes prominent absorptions which can be assigned to cation products. It has previously been established that the ylidion (H2CXH+) isomers have stable potential minima and that H2CFH+ is lower in energy than CH3F+. The identification of the new absorptions is aided by experimental studies on isotopically substituted Ne:CH3X samples and by ab initio calculations of the structures and vibrational fundamentals of both CH3X+ and H2CXH+. In each of the three systems, a prominent absorption which is intermediate in frequency between the gas-phase (and neon-matrix) absorptions of HX and HX+ can be assigned to the ylidion, as can be several other absorptions. Still other absorptions can be assigned to CH3Cl+ and CH3Br+. The behavior of the product absorptions on exposure of the deposit to filtered visible and ultraviolet ra...

Matrix isolation study of the interaction of excited neon atoms with O3: Infrared spectrum of O−3 and evidence for the stabilization of O2⋅⋅⋅O+4

When a Ne:O3 sample is codeposited at approximately 5 K with neon atoms that have been excited in a microwave discharge, the most prominent infrared absorptions of the resulting solid are contributed by trans‐ and cyc‐O+4 and by O−3. The failure to detect infrared absorptions of O+3 is consistent with the initial formation of that species in one or more dissociative excited states. The ν3 absorption of O−3 appears at 796.3 cm−1, close to its position in earlier argon‐matrix experiments in which photoionization of an alkali metal atom provided the electron source and in which diffusion of the atomic cation would result in the stabilization of appreciable M+O−3. The identification of O−3 isolated in solid neon is supported by observations of O−3 generated from isotopically substituted Ne:O2:N2O samples, also codeposited with excited neon atoms. An upper bound of 810 cm−1 is estimated for the gas‐phase band center of ν3 of O−3. Infrared absorptions which grow on mild warmup of the sample are tentatively assi...

Matrix isolation study of the interaction of excited neon atoms with allene and propyne: Infrared spectra of H2CCCH2+ and H2CCCH−

When a Ne:allene or a Ne:propyne sample was codeposited at approximately 5 K with a sample of pure neon that had been excited in a microwave discharge to provide a 16.6–16.85 eV energy source, prominent new infrared absorptions which can be assigned to the H2CCCH2+ cation appeared. Also present in the allene experiments were two absorptions which can be assigned to H2CCCH−. In the propyne experiments, an absorption is tentatively attributed to the strongest infrared fundamental of CH3CCH+. The structures and vibrational fundamentals obtained from density functional and ab initio calculations for various isotopomers of H2CCCH2+, CH3CCH+, cyc-C3H3+, H2CCCH+, and H2CCCH− are given. The infrared absorption pattern of the cation common to the allene and propyne experiments matches that of the predominant gas-phase product, cyc-C3H3+, reasonably well, except for the presence of extra peaks in the CH-stretching region. However, comparison of the results of experiments on isotopically substituted samples with the...

Investigation of the collision‐induced absorption by O2 near 6.4 μm in pure O2 and O2/N2 mixtures

The collision-induced fundamental vibrational band of molecular oxygen has been measured between 1300 and 2000 cm -1 using a Fourier-transform infrared spectrometer and an optical path length of 84 m. Spectra were recorded for pure O 2 and O 2 /N 2 mixtures at densities up to 10 times the density of an ideal gas at standard temperature (273.15 K) and pressure (101.325 kPa), and for temperatures between 228 and 296 K. The band is dominated by the ΔJ = 0, Q branch and the ΔJ = 2, S and ΔJ = -2, O branch shoulders, with the S branch exhibiting ripples previously attributed to bound dimer transitions, pure quadrupole transitions of O 2 perturbed by line mixing, and intercollisional interferences. The ripples are seen at the same wavenumbers in O 2 -Ar mixtures, with intensities dependent on both the O 2 and Ar densities, suggesting that the ripples are not due to bound dimer transitions. The integrated band intensity S is related to the collision-induced absorption coefficients by S = S O2-O2 ρ O2 2 + S O2-N2 ρ O2 ρ N2 , where S O2-O2 and S O2-N2 are the integrated binary collision-induced absorption coefficients for O 2 -O 2 and O 2 -N 2 collisions, respectively, and ρ O2 and ρ N2 are the O 2 and N 2 gas densities. We find values for S O2-O2 = 6.972(66) × 10 -4 cm -2 and S O2-N2 = 7.12(22) × 10 -4 cm -2 , respectively, at 296 K, when the gas density is equal to that found at STP (i.e., S O2-O2 = 6.972(66) × 10 -4 cm -2 amagat -2 and S O2-N2 = 7.12(22) × 10 -4 cm -2 amagat -2 ).

Vibrational Spectra of Molecular Ions Isolated in Solid Neon. XV. Infrared Spectroscopic Evidence for NeHF+ and HFFH+

When a Ne:HF 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 to NeHF+ and HFFH+. Evidence is presented suggesting that neon-matrix shifts may be anomalously large for protonated molecules which are derived from species with proton affinities near or below 550 kJ/mol. The results of earlier ab initio studies, as well as those of the present experimental and ab initio studies, indicate that the NeHF+ complex is quite strongly bound. The ν3 absorptions of NeHF+ and NeDF+ and the ν1+ν3 absorption of NeHF+ are tentatively identified. An absorption at 3064.7 cm−1 has isotopic substitution behavior appropriate for its assignment to HFFH+. Density functional calculations were performed in order to estimate the positions of the harmonic vibrational fundamentals of HFFH+-dn, and a more elaborat...