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Production and consumption of CFC-11 (trichlorofluoromethane, CCl3F), CFC-12 (dichlorodifluoromethane, CCl2F2) and CCl4 (carbon tetrachloride) are controlled under the regulations of the Montreal Protocol and have been phased out globally since 2010. Only CCl4 is still widely produced as a chemical feedstock. After 2010, emissions of CFC-11 and CFC-12 should therefore mostly originate from existing banks (e.g. from foams, mobile air conditioning units and refrigerators); however evidence has emerged of an increase in global emissions of CFC-11 in the last decade, some of which has not been fully accounted for. The motivation for this work was to assess the emissions of CFC-11, CFC-12 and CCl4 from western Europe. All countries in this region have been subject to the controls of the Montreal Protocol since the late 1980s and, as non-Article 5 Parties, have been prohibited from producing CFCs and CCl4 for dispersive use since 1996. Four different inverse modelling systems are used to estimate emissions of these gases from 2008 to 2021 using data from four atmospheric measurement stations: Mace Head (Ireland), Jungfraujoch (Switzerland), Monte Cimone (Italy) and Tacolneston (UK). The average of the four model studies found that western European emissions of CFC-11, CFC-12 and CCl4 between 2008 and 2021 were declining at 3.5 % yr−1 (2.7 % yr−1–4.8 % yr−1), 7.7 % yr−1 (6.3 % yr−1–8.0 % yr−1) and 4.4 % yr−1 (2.6 % yr−1–6.4 % yr−1), respectively. Even though the emissions were declining throughout the period, the area including northern France, Belgium, the Netherlands and Luxembourg showed consistently elevated emissions of CFC-11 compared with the surrounding regions. Emissions of CFC-12 were slightly elevated in the same region. CCl4 emissions were the highest in the south of France. France had the highest emissions of all three gases over the period 2008–2021. Emissions from western Europe (2008–2021) were on average 2.4 ± 0.4 Gg (CFC-11), 1.3 ± 0.3 Gg (CFC-12) and 0.9 ± 0.2 Gg (CCl4). Our estimated decline in emissions of CFC-11 is consistent with a western European bank release rate of 3.4 % (2.6 %–4.5 %). This study concludes that emissions of CFC-11, CFC-12 and CCl4 have all declined from 2008 to 2021 in western Europe. Therefore, no evidence is found that western European emissions contributed to the unexplained part of the global increase in atmospheric concentrations of CFC-11 observed in the last decade.

Global emissions of the ozone depleting gas 1,1-dichloro-1-fluoroethane (HCFC-141b, CH3CCl2F), derived from measurements of atmospheric mole fractions, have been rising between 2017–2021 despite a fall in reported production and consumption for dispersive uses. This study evaluates the possible drivers behind this renewed rise in emissions. HCFC-141b is a controlled substance under the Montreal Protocol, and its phase-out is currently underway, after a peak in reported consumption and production in developing countries (Article 5) in 2013. If reported production and consumption are correct, it suggests that the 2017–2021 rise is due to an increase in emissions from the bank when HCFC-141b containing appliances reach the end of their life, or from production of HCFC-141b not reported for dispersive uses. Regional emissions have been estimated between 2017–2020 for all regions where measurements have sufficient sensitivity to emissions. This includes the regions of northwestern Europe, east Asia, the USA and Australia, where emissions decreased by a total of 1.6 ± 3.9 Gg yr−1, compared to a mean global increase of 3.0 ± 1.2 Gg yr−1 over the same period. Collectively these regions only account for around a third of global emissions in 2020. Therefore we are not able to pinpoint the source regions or specific activities responsible for the recent global emission rise.

Previous studies have shown that electroacupuncture (EA) can induce cardioprotection against ischemia-reperfusion (IR) injury, but its mechanisms are incompletely understood. We have previously shown that several other forms of remote preconditioning of the heart work, at least in part, via the release of circulating cardioprotective factors into the bloodstream, that can be dialyzed and subsequently shown to reduce IR injury in isolated hearts. We used the same methods to assess whether EA leads to similar humoral cardioprotection. EA rabbits were subjected to 60 min of bilateral stimulation at the Neiguan point, following which their blood was drawn, dialyzed, and used to perfuse hearts in Langendorff preparation and subsequently subjected to 60 min of global ischemia and 120 min of reperfusion. Compared to controls, dialysate from EA animals led to significant reduction in infarct size and improved functional recovery. The degree of cardioprotection was no different to that seen in animals randomized to receive remote preconditioning using transient limb ischemia (4 cycles of 5 min ischemia/5 min reperfusion). These results suggest that EA recapitulates the cardioprotection achieved by remote preconditioning, by similarly leading to release of circulating cardioprotective factors.

Fourier transform infrared (FTIR) absorption spectra in the 2000 to 3500 cm–1 range are reported for the gaseous 16 O, 16 O- and 18 O, 18 O-isotopomers of tropolone[OH(OD)] at 25 oC. The spectral doublet component separations are near 20 and 19 cm–1 for 16 O, 16 O- and 18 O, 18 O-Tp(OH), respectively, and near 7 and 6.5 cm–1 for 16 O, 16 O- and 18 O, 18 O-Tp(OD). The spectra suggest the tautomerization tunneling mechanisms in these states are complex multidimensional processes including the participation of IVR. In general, the OHO isotope effects demonstrate a mixing of O atom displacement coordinates into the intramolecular dynamics for most of the vibrational states observed in the fundamental CH/OH(OD) stretching regions.

Computational studies of 12 64-electron homologues and isomers of tropolone in the S(0) electronic ground state are reported. Three minimum-energy structures, tropolone (Tp), 5-azatropolone (5Azt), and 5-H-5-azatropolonium (5AztH(+)), have an internal H-bond and planar C(s)) geometry, and three, tropolonate (TpO(-)), 5-azatropolonate (5AzO(-)), and 1-H-azepine-4,5-dione (45Di), lack the H-bond and have twisted C(2) geometry. All 6 substances have an equal double-minimum potential energy surface and a saddle point with planar C(2)(v) geometry. The energy for the gas-phase isomerization reaction 45Di --5Azt is near +4 kJ mol(-1) at the MP4(SDQ)/6-311++G(df,pd)//MP2/6-311++G(df,pd) (energy//geometry) theoretical level and around -20 kJ mol(-1) at lower theoretical levels. The dipole moments computed for 45Di and 5Azt are 9.6 and 2.1 D, respectively, and this large difference contributes to MO-computed free energies of solvation that strongly favor--as experimentally observed--45Di over 5Azt in chloroform solvent. The MO-computed energy for the gas-phase protonation reaction 45Di + H(+) --5AztH(+) is -956.4 kJ mol(-1), leading to 926.8 kJ mol(-1) as the estimated proton affinity for 45Di at 298 K and 1 atm. The intramolecular dynamical properties predicted for 5Azt and 5AztH(+) parallel those observed for tropolone. They are therefore expected to exhibit spectral tunneling doublets. Once they are synthesized, they should contribute importantly to the understanding of multidimensional intramolecular H transfer and dynamical coupling processes.

Theoretical studies have been carried out to elucidate the ground-state unimolecular decomposition channels for propynoic acid (PA) in the gas phase. In this paper we present details of mechanisms for the decarboxylation and decarbonylation channels of PA. The transformations of PA result in the formation of carbon dioxide and acetylene from the decarboxylation channel while carbon monoxide and hydroxyacetylene, ultimately the ketene, are formed from the decarbonylation pathway. Equilibrium structures and the principal transition states (TSs) for each pathway have been identified and characterized. The Gaussian 98 suite of programs and MOLDEN were used for computation and visualization. All computations of equilibrium and TS structures relevant to the two competing unimolecular decomposition channels (decarboxylation and decarbonylation) were performed with second-order Moller–Plesset (MP2) and Becke's three-parameter exchange functional and the gradient-corrected functional of Lee, Yang, and Paar (B3LYP) levels using the 6-31G(d,p), 6-311++G (d, p) and Dunning's correlation-consistent polarized valence basis set (aug-cc-pVDZ). The geometries were fully optimized and characterized as minima (0 imaginary frequencies) or first-order saddle points (1 imaginary frequency) by harmonic vibrational analysis at the MP2/6-311++G(d,p) and B3LYP/6-311++G(d,p) levels. All the calculations indicate that the lowest energy decomposition pathway for PA is decarboxylation. Decarboxylation of PA occurs most easily through a three-step mechanism: conversion of s-cis-HCCCO2H to s-trans-HCCCO2H, followed by a 1, 3-hydrogen migration of hydroxyl hydrogen, resulting in a four-center TS that decays easily to acetylene and carbon dioxide, with an activation barrier of 61.3–79.9 kcal/mol (average 65.67 kcal/mol). Decarbonylation, leading to hydroxyacetylene (and subsequently the ketene) and carbon monoxide, occurs easily via a direct (one-step) three-center TS. The direct (one-step) elimination of carbon monoxide from propynoic acid has a calculated average activation barrier of 67.9–81.7 kcal/mol (average, 74.1 kcal/mol). The decarboxylation pathway is shown to occur with a maximum exothermicity of 28 kcal/mol. On the contrary, the decarbonylation of PA is predicted to occur with an overall endothermicity of ≈29.2 kcal/mol for formation of hydroxyacetylene and carbon monoxide and an average exothermicity of −7.69 kcal/mol for formation of the ketene and carbon monoxide. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Nitrogen pressure broadening effects are observed on the high resolution ( 0.0025 cm −1 ) FTIR spectrum of gaseous tropolone at 298 K and 32 m of path length. Broadening observations on narrow absorption spikes contribute to understanding of the spectroscopy and dynamics of tropolone in several ways. First, they help to establish a remarkable progression of sharp peaks near 752 cm −1 as a part of the Q branch of the anharmonic ν22 (COH torsion) fundamental. The subband spacings of about 0.005–0.010 cm −1 are too large to be determined by harmonic vibrational differences in the rotational constants alone and are attributed to vibration–contortion–rotation perturbations of the upper state (ν22) energy levels of this anharmonic and relatively large amplitude vibration. Second, the isolated and sharp Q branch spikes near 915 cm −1 allow first estimates to be made for effective composite pressure broadening coefficients of tropolone–N2 collisions. The coefficients for transitions within the Ncon=0 and Ncon=1 contortion states differ from each other. They are relatively small due to the preponderance of high rotational states in their composition. Third, N2 broadening effects on substructure in the Q branch doublet near 754 cm −1 help support the assignment of this doublet to tunneling structure of the ν37 fundamental (contortion or incipient skeletal tunneling). The observed doublet components appear as perturbatively IR enhanced three and five peak fragments of weak longer progressions. The parallel spectroscopic behaviors of the perturbed anharmonic ν22 and ν37 vibrations differ markedly from behavior observed for the quasiharmonic vibrations.

The infrared absorption spectrum of tropolone vapor at 25 °C, ∼0.01 Torr, and 32 m path length has been recorded from 960 to about 700 cm-1 at a resolution of 0.0025 cm-1. Twenty-nine cold band and hot band spectral tunneling doublets marked by sharp type A or type C Q branch apexes protruding from the congested vibration−contortion−rotation absorption profiles are assigned. Twenty-six vibration-contortion state-specific splittings are estimated for tropolone in its ground electronic state. This number is currently unprecedented in the literature for any sizable molecule. About half of these quasiharmonic vibrational states show an appreciable quenching of tunneling due to increased effective barriers and/or path lengths and, in the case of the nominal COH torsion, the tunneling is reduced to 0.07 of the zero-point (ZP) value of 0.974 cm-1. The analysis is guided by predictions of the independent {tunneling skeleton}{tunneling H atom} tautomerization model that was previously applied to the vibrational sp...

The minimum energy pathway leading between the tautomers of tropolone was calculated using molecular orbital (MO) methods. This, with various 1D and 2D cuts of the potential energy surface (PES) topography, reveals the {tunneling skeleton}/{tunneling H atom} mechanism for tautomerization. In the zero-point states the H atom is localized to one of the O atoms until the tropolone skeleton becomes sufficiently vibrationally displaced towards C2v configurations that near-equal double-minimum potential energy functions (PEFs) arise for the H atom vibration. The resulting delocalization of the H atom between the two O atom sites allows the skeletal displacement to proceed through the barrier and the tautomerization process to be completed. The v1 (OH stretching) energies in quantum states N1 are strongly dependent on the skeletal geometry and, adiabatically separated from the slow v22 vibration, they contribute to markedly different 1D effective potential energy functions V22eff[N1] for v22. V22eff[N1=0] is a n...

Infrared spectra of tropolone(OH) and tropolone(OD) obtained from vapor phase, solvated, and rare gas matrix-isolated samples, and from fluorescence dip infrared spectroscopy experiments by Frost et al. on jet-cooled samples, are analyzed with the guidance of high level ab initio molecular orbital (MO) computations. It is found that the anharmonicity of the double minimum global potential energy surface of S0 tropolone is manifested by multistate local resonance networks coupling fundamental vibrations to nearby overtone and combination states. These resonance networks pervade the IR spectrum of tropolone above 500 cm−1, and the absorbances are much more strongly perturbed from harmonic level predictions than the frequencies. Some of the IR absorbances are also sensitive to intermolecular interactions. At maximum spectral resolutions reaching ∼0.2 cm−1 only the v1 and v22 (OH stretching and nascent skeletal tunneling) vibrations show resolved vibrational state-specific tunneling doublets. The tunneling be...

The symmetrical geometries of 1,3-cyclobutadiene (CB) and substitutional vacancies in crystalline fcc Ar allow purely ab initio MO estimations to be made for the stabilization energies of several symmetric trapping sites in the Ar/CB matrix system at the MP2/6-311++G(2d,2p) [denoted HI-MO] level of theory. The single-substitutional vacancy supports the most stable trapping site in the HI-MO Ar/CB system. It was examined by filling an Ar13 vacancy of the HI-MO Ar lattice with a symmetrical CB:Ar12 kernel cluster, with dilation of the kernel cluster opposed by a symmetrical HI-MO lattice distortion PEF derived for the purpose. In addition, various supplemental HI-MO stabilization energies were computed. Slightly displacing the four nearest-neighbor Ar atoms coplanar with CB from square-planar geometry shows this site distortion PEF is very soft. The results suggest fluxional behavior for the Ar atoms near the CB guest molecule and the soft trapping site environment provides access to equivalent global PES m...

MO computations of vibrational spectra for 1,3-cyclobutadiene (CB) and CB:CO2 van der Waals molecule isotopomers at the MP2/6-311++G(2d,2p) level of MO theory are analyzed together with the extensive Ar/CB matrix-isolation spectra of the Michl group, the low 3.2 kcal/mol (ZPE-corrected) MO-computed energy of the square-planar saddle-point for CB reported by Nakamura et al., and opportune one-dimensional analysis of the automerization energy levels of 12C4H4. The composite interpretation results in the assignment of the strongly anharmonic Raman transitions of Ar/CB observed at 723 and 1678 cm−1 to the E2-E0 and E4-E0 transitions, respectively, in the automerization coordinate. The 13C and D isotope dependencies of the nominal C=C stretching and δCH wagging vibrational normal modes of the CB valence isomers depend markedly on whether the labeled HC=CH moieties of CB are mass equivalent or not, and the pronounced normal mode differences are viewed as providing different gateways into the global anharmonic PES domains. The automerization coordinate Qa originates as the nominal C=C stretching normal coordinate of ag symmetry, followed by a curving to more efficiently interchange the C=C and C–C bond lengths as the square-planar D4h configuration is approached. The latter is crossed at a geometry dilated with respect to the saddle-point, thereby providing a barrier configuration about 5 kcal/mol above the PES minima (i.e., a dilation energy of about 2 kcal/mol plus the 3.2 kcal/mol saddle-point energy). The computed zero-point levels of 12C4H4 (1-D modeling) are separated by E1-E0=11 cm−1 to suggest ZP tunneling rates reaching the picosecond time scale. The analysis exposes new aspects of the intramolecular dynamics of CB, and the proposed automerization mechanism accounts for all of the presently known information pertaining to this interesting property of the cyclobutadiene molecule.

Infrared (IR) spectra of the 6,7Li isotopomers of the LiF species isolated in rare gas matrices are interpreted with the input of molecular geometries and vibrational spectra computed using ab initio molecular orbital (MO) theory at the MP2/6‐31G* level. The MO computations, together with IR matrix‐isolation observations, support firm species assignments and vibrational assignments for the IR‐active modes of the title molecules. The study presents the first evidence for the existence of matrix‐isolated Li4F4 cyclic tetramer, and resolves contradictory species/vibrational assignments for the smaller oligomers. Most of the matrix‐isolated cyclic trimer and tetramer population is formed by coalescence of smaller species during the matrix deposition process or during subsequent matrix annealing/warming processes. There appears to be no evidence in the available matrix‐isolation data for the existence of a matrix‐stabilized Li2F2 linear dimer.

Infrared spectra of the LiF monomer isolated in rare gas and RG/X mixed‐matrices are interpreted with the guidance of ab initio molecular orbital (MO) computations performed on FLiArn clusters and on FLiX van der Waals complexes (X=Ar, N2, CO, O2, and CH4). The work suggests there are two distinct trapping subsites for LiF in a single‐substitutional vacancy of the Ar fcc crystal. In the primary subsite LiF lies on a tetragonal crystal axis and makes four near‐optimal LiAr contacts; in the metastable subsite it lies on a trigonal axis and makes three near‐optimal LiAr contacts. The model is supported by its account of the large Ar‐induced vibrational frequency shift, spectral doublet, and temperature‐dependent infrared (IR) absorption profile of the LiF vibrational fundamental. IR observations of LiF isolated in several RG/X mixed matrices support the existence of FLiX van der Waals complexes isolated in Ar double‐substitutional sites of the lattice.

The fluorescence excitation spectrum of the lowest allowed singlet–singlet transition of jet‐cooled 2,5‐dihydroxy‐p‐benzoquinone is reported. The transition is assigned as S3←S0, 1Bu←1Ag, π*←π and the 0–0 band origin is at 275.55 nm. Twenty vibrational levels, which include half of the Ag fundamentals, are assigned for the S3 state. The observed laser‐induced fluorescence transitions are structureless peaks with bandwidths that depend on the intensity of the excitation laser. No spectral multiplets attributable to intramolecular tunneling were observed. Deuterium isotope shifts of the 0–0 transition are +21 cm−1 per internal hydrogen bond. The 0–0 transitions of hydrate isotopomers with hydration shifts of only +11 cm−1 per water molecule are reported.

The fluorescence excitation spectrum of the lowest allowed singlet–singlet transition of jet‐cooled 2,5‐dihydroxy‐p‐benzoquinone is reported. The transition is assigned as S3←S0, 1Bu←1Ag, π*←π and the 0–0 band origin is at 275.55 nm. Twenty vibrational levels, which include half of the Ag fundamentals, are assigned for the S3 state. The observed laser‐induced fluorescence transitions are structureless peaks with bandwidths that depend on the intensity of the excitation laser. No spectral multiplets attributable to intramolecular tunneling were observed. Deuterium isotope shifts of the 0–0 transition are +21 cm−1 per internal hydrogen bond. The 0–0 transitions of hydrate isotopomers with hydration shifts of only +11 cm−1 per water molecule are reported.

Fourier transform infrared absorption spectra containing evidence for about two dozen spectral tunneling doublets are reported for gaseous tropolone(OH), tropolone (OD), and 18O,18O-tropolone(OH) in the 800 to 300 cm-1 spectral range. No FTIR absorption was detected in the 300-150 cm-1 range. The known zero-point (ZP) tunneling splitting values Delta0 = 0.974 cm-1 for tropolone(OH) (Tanaka et al.) and 0.051 cm-1 for tropolone(OD) (Keske et al.) allow vibrational state-specific tunneling splittings Deltav to be estimated for fundamentals including three with strong O...O stretching displacements [cf. for tropolone(OH) nu13(a1) = 435.22 cm-1 with HDelta13 = 1.71 cm-1 = 1.76 HDelta0, and for tropolone(OD) nu13(a1) = 429.65 cm-1 with DDelta13 = 0.32 cm-1 = 6.27 DDelta0]. The majority of Deltav splittings in the sub-800 cm-1 range are dilated relative to the isotopomer Delta0 values. The FTIR spectra demonstrate the presence of dynamic couplings and potential function anharmonicity in addition to revealing Deltav splittings and many OH/D and 18O/16O isotope effects. Approximate values are obtained for the ZP splittings 88Delta0 and 86Delta0 of the doubly and singly 18O-labeled isotopomers of tropolone(OH). The diverse values of the observed Deltav/Delta0 splitting ratios underscore the inherent multidimensionality and corner-cutting activities entering the state-specific tunneling processes of the tropolone tautomerization reaction.

Properties of dihydroxycarbene in its S 0 ( 1 A 1 ) and T 1 ( 3 B ) electronic states are investigated using MO methods at basis-set levels including polarization functions and approximations for electron correlation. The energetics of addition reactions and the properties of adducts formed between (HO) 2 C and H 2 , NO, N 2 , O 2 or H 2 O are considered. The adducts include methanediol and methanetriol, 3,3-dihydroxydiazirine and dihydroxydiazomethane, dihydroxynitrosomethyl, singlet dihydroxyoxirane, triplet dihydroxydioxymethane, and the dihydroxyketone oxide (HO) 2 COO.

Laser excitation spectra with v=0, 2, 4, and 6 in the A 1B2–X 1A1 26v0 progression of jet‐cooled 18O/16O isotopomers of tropolone are reported. The isotope shift for ν26, an out‐of‐plane deformation mode at 39 cm−1 in the A state, is 2% for tropolone‐18O18O. This large 18O isotope effect indicates that Q26 for tropolone resembles the analogous normal mode of tropone, which is a ring deformation towards the boat conformation of 2, 4, 6‐cycloheptatriene accompanied by a large O atom displacement. Tunneling by tropolone in the A state is quenched by exciting the 26v overtone states and a mechanism for this quenching is proposed in terms of the indicated normal coordinate. Tunneling splittings are

Calculs optimises ab initio MO(6-31G* de la geometrie et du moment dipolaire. Calculs 6-31G du spectre vibrationnel, des intensites IR et Raman

The Fourier transform infrared spectrum of tropolone(OH) vapor in the 1175-1700 cm(-1) region is reported at 0.0025 and 0.10 cm(-1) spectral resolutions. The 12 vibrational fundamentals in this region of rapidly rising vibrational state density are dominated by mixtures of the CC, CO, CCH, and COH internal coordinates. Estimates based on the measurement of sharp Q branch peaks are reported for 11 of the spectral doublet component separations DS(v) = |Delta(v) +/- Delta(0)|. Delta(0) = 0.974 cm(-1) is the known zero-point splitting, and three a(1) modes show tunneling splittings Delta(v) approximately Delta(0), four b(2) modes show splittings Delta(v) approximately 0.90Delta(0), and the remaining four modes show splittings Delta(v) falling 5-14% from Delta(0.) Significantly, the splitting for the nominal COH bending mode nu(8) (a(1)) is small, that is, 10% from Delta(0). Many of the vibrational excited states demonstrate strong anharmonic behavior, but there are only mild perturbations on the tautomerization mechanism driving Delta(0). The data suggest, especially for the higher frequency a(1) fundamentals, the onset of selective intramolecular vibrational energy redistribution processes that are fast on the time scale of the tautomerization process. These appear to delocalize and smooth out the topographical modifications of the zero-point potential energy surface that are anticipated to follow absorption of the nu(v) photon. Further, the spectra show the propensity for the Delta(v) splittings of b(2) and other complex vibrations to be damped relative to Delta(0).

Infrared-absorption profiles observed for vibrational transitions of gaseous tropolone often show sharp Q branch peaks, some of them ultranarrow spikes, indicative of the band origins for vibrational state-specific spectral tunneling doublets. In this work oxygen isotope effects for two CH wagging fundamentals, the COH torsion fundamental, and the skeletal contortion fundamental are reported. They allow considerations to be given: (1) oxygen isotope effects on the vibrational frequencies and state-specific tunneling splittings; (2) the asymmetry offset of the potential-energy minima for O16 and O18 tropolone; and (3) additional details concerning previously proposed high J rotation-contortion resonances in the contortional fundamental. The new results help to characterize the skeletal contortion fundamental and support the joint participation of skeletal tunneling with H tunneling in the vibrational state-specific tautomerization processes of tropolone in its ground electronic state.

Intermolecular potential energy functions associated with the solvation of small molecules affect their chemical reactivity and other properties of general importance. Matrix-isolation sampling can provide prototype solvation conditions for some molecules, and spectroscopic studies can yield matrix-induced vibrational frequency shifts and other resolved data for heavy atom isotopomers. In this discussion vibrational isotope effects for small matrix-isolated molecules [e.g. HCOOH and (LiF)1,2,3,4] are considered with respect to their behavior in different matrices [e.g. Rg, N2, CO, CO2]. A goal for this type of research is an evaluation of the use of the matrix perturbation of isotope effects as a tool for characterizing matrix trapping sites and for exposing important anharmonicities in the vibrational PEF of the solute molecule.

Intramolecular H tunneling is often analyzed using 1-D theoretical models, or improved models providing a minimum energy pathway defined by model 2- or 3-D PEFs, or models coupling a 1-D tunneling coordinate to a vibrational bath representing all other modes. The analysis of a tunneling coordinate strongly coupled to one or two heavy atom vibrational modes is of much current interest. This problem, which includes heavy atom vibrational-assisted H tunneling, is experimentally accessible to the methods of low-temperature spectroscopy on molecular beam, matrix-isolated, and solid state samples. Heavy atom effects on intramolecular H tunneling, primarily as observed by optical spectroscopy, are considered in this discussion.

Large (6.9 to 16.3 cm−1 ) tunneling splittings are uniquely observed for the ν27 (OD stretch), ν31 (carbonyl stretch), and ν34 (C=C–C stretch) fundamentals of tropolone‐OH and tropolone‐OD in the X 1A1 (ground) electronic state. These same three modes are predicted by the molecular geometry to interact strongly with tunneling because the dominant vibrational and tunneling displacements involve the same atoms. The heavy atom tunneling displacements (≊0.07 A) are small enough to plausibly consider heavy atom tunneling phenomena—especially in appropriate excited vibrational states—and the tunneling splittings appear consistent with behavior expected at zero order for adiabatic reaction surface theory with a 2D reaction surface defined by C=O/C–O and C=C–C heavy atom coordinates. This model attributes tunneling in the X state of tropolone to heavy atom motion followed adiabatically by H atom motion rather than the reverse. Energy balance equations are used to obtain estimates for the vibrational state‐speci...

Infrared spectra of glyoxylic acid monomers, including the hydroxyl deuterated and general O-18 isotopomers, are reported for argon and nitrogen matrix-isolated samples in the range 400–4000 cm−1. Values for all 15 fundamental vibrations of the intramolecular H-bonded monomer are listed. Bands attributed to the trans-carbonyl conformer with a free car☐yl group are also observed and about half of its fundamental frequencies are listed. Some modes of the intramolecular H-bonded glyoxylic acid monomer are strongly matrix dependent, and differences between Ar and N2 matrix spectra are exploited in sorting out the spectral information.

Infrared spectra of monomeric oxalic acid-h2, -hd and -d2 have been observed using neon matrix-isolation spectroscopy. In addition, spectra of oxalic acid-h2, vapor were obtained using a heated absorption cell with a 10 m pathlength. All IR active fundamentals are assigned for oxalic acid-h2, and -d2, except the low frequency torsion. The spectra are interpreted in terms of the C2h intramolecularly hydrogen bonded model. Two vibrational assignments are discussed; one involves a very large intensity for the v8 + v11 (COH torsion) combination band of oxalic acid-h2. Tentative values for several Raman active fundamentals of oxalic acid-h2 are suggested using possible combination bands. Few fundamentals of oxalic acid-hd correlating with the Raman modes of the symmetric monomers could be observed. A force constant analysis of the by secular block is presented.

A previously undetected perturbation in the HCCH A 1Au 3ν3 (trans‐bend) level has been found and analyzed. The perturbing level is identified as the A 1Au ν2+2ν4 level. Locally deperturbed molecular constants for the 3ν3 and perturbing level are obtained, along with the perturbation matrix element and the J‐dependent mixing coefficients. The A‐state torsional fundamental, ν4≈850 cm−1, is estimated from the energy of perturbing level. The presence of the perturbation explains large differences between the rotational line intensity patterns observed in the absorption and fluorescence excitation spectra. The perturbed 3ν3 and extra lines are especially prominent in a fluorescence excitation spectrum of the A 1Au–X 1Σ+g 33 0 K10 subband of acetylene rotationally cooled in a supersonic jet.

The results of molecular orbital calculations performed for the oxalic acid monomer using the 6‐31G, 6‐31G*(5d), 6‐31G**(5d), and MP2/6‐31G*(5d) levels are reported. At the latter three levels of approximation the geometry with intramolecular hydrogen bonds is calculated to have the lowest energy, and the energies calculated for planar rotational conformers fall within about 2 kcal/mol of one another. The barrier hindering internal rotation of the carboxyl groups about the C–C bond for the nonhydrogen bonded conformer is calculated to be less than 1 kcal/mol, and secondary potential energy wells for gauche, rather than for the expected cis, carbonyl orientation are found about 300 cal/mol above the trans conformer at the 6‐31G level. Vibrational frequencies calculated at the 6‐31G level for the H‐bonded conformer average about 9% higher than the observed values. On including electron correlation at the MP2 level the barrier calculated for the concerted, symmetrical, transfer of two protons between equivalent potential energy minima is 31.9 kcal/mol. This value is probably an upper bound. When electron correlation is ignored, calculations for the transfer of a single proton lead to a potential energy well that stabilizes an (HO)2CCO2 configuration with C2v symmetry at an energy 26–28 kcal/mol above that of the H‐bonded ground state conformer. When electron‐correlation is included at the MP2 level there is a saddle point in the PES instead. This is the transition state for proton exchange by successive transfers, and a search for its position at the MP2 level was not made. However, energy values of 25.7 and 36.6 kcal/mol are calculated using MP2/6‐31G*(5d) at optimized 6‐31G critical point geometries, and these values are taken as temporary estimates for the MP2 level transition state energies for two‐step proton exchange and for decarboxylation, respectively. It remains to be determined whether the stepwise proton exchange channel will be present for higher level calculations. The results of these MO calculations are consistent with the experimental observations of Lapidus, Barton, and Yankwichyielding first order kinetics, a low activation energy (31.5 kcal/mol), and complex kinetic isotope effects for the thermal decarboxylation of the oxalic acid monomer. Because of its importance in this reaction, calculations of the 1,2 H atom shift of dihydroxycarbene are also reported.

Present address of Duane R, Kirklin: National Bureau of Standards, Washington, D. C., 20234. Ellis R, Lippincott: Posthumous.

Six recently reported intermolecular potential energy functions for HF–HF interactions are examined and used to calculate classical second virial coefficient curves. Order of magnitude differences exist among the six B(T) curves and none of them decreases with temperature as rapidly as an experimental curve determined in the 19.5–56 °C range. The HF3 potential of Klein, McDonald, and O’Shea appears to give the best overall description of HF–HF interactions and this function is used to calculate properties of several higher (HF)q oligomers. The resulting low energy conformations are cyclic, and the hexamer has a puckered, nonrigid structure. The calculated hydrogen bond energies, F⋅⋅⋅F distances, and the puckered, nonrigid hexamer structure all agree well with the available experimental information.

Infrared spectra of acrylyl chloride have been measured in argon and nitrogen matrices, in a heated vapor cell, and in a long path vapor cell. The results reaffirm the earlier conclusion of Katon and Feairheller ( J. Chem. Phys. 47 , 1248 (1967)) that vapor phase acrylyl chloride exists as a mixture of two rotational conformers. The new information leads to an assignment of the 18 fundamental modes of the s- trans rotamer and to many of those of the second (s- cis ) rotamer. Several frequencies appear to be insensitive to isomerization. The potential energy difference between the two rotamers appears to be small in the vapor phase and the potential energy barrier separating the two minima is sufficiently high that direct matrix isolation of both rotamers is possible before relaxation to the low energy form can occur.