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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.

Several hydrogen peroxide infrared absorption bands have been obtained under 0.2 cm—1 resolution. They demonstrate both doubling due to internal rotation and effects due to the inertial asymmetry. The ground‐state rotational constants are found to be: A″=10.068 cm—1, B″=0.8740, C″=0.8384. These parameters indicate a wide dihedral angle for H2O2, as proposed in the following structure: OO bond=1.475 A, OH bond=0.950 A, dihedral angle=119.8°, and OOH angle=94.8°.The constants are applied to the microwave data for H2O2 and the deuterated species. The ground‐state splitting is found to be 11.44 cm—1, and this, used with the recently reported torsion at 317 cm—1, yields the barriers hindering internal rotation. They are Vcis=1300 cm—1 and Vtrans=300 cm—1. A simple correlation of the infrared doublings is attempted.

The vibrational F matrix can be written in the parameterized form F = L0+−1 C+−1 ΛC−1L0−1, where L0 is determined from the G matrix alone; Λ is from the vibration frequencies; and C is an orthogonal matrix of N(N−1) 2 parameters φij. The restoring forces for internal coordinates or symmetry coordinates are calculated as a function of the φij parameters. Conditions on the restoring forces and energy are proposed that can be summarized in the equation F steep = Σ i T i D ii − 1 2 . The critical points of Fstp or certain “intersection” points (e.g., T 1 F 22 − 1 2 = T 2 F 11 − 1 2 for N = 2) determine the several mathematically acceptable sets of φij parameters. The molecular “true” F matrix has near-maximum parameterized restoring forces for coordinates associated with the highest vibration frequencies. In the Fstp equation, the Ti are geometrical factors derived using the virial theorem (e.g., T1 = r and T2 = 2 cosθ for C2v triatomic molecules) and the Dii are cofactors of the diagonal force constants. The method is illustrated with two-, three- and four-dimensional examples including F2O, NF3, ONF, H2S2 and other molecules. The force constants determined using the new method with the vibration frequencies of a single molecule compare very well with those determined by conventional methods using isotopic substitution, Coriolis coupling constants, and centrifugal distortion constants. For many molecules the F matrix is determined uniquely by knowledge of the vibrational assignment, since only one F matrix solution occurs with the proper assignment; in other cases, a certain minimal amount of additional information beyond the vibration frequencies and geometry may be necessary in order to select the “true” F matrix. For example, the DJK centrifugal distortion constants can isolate the true F matrices for the nitrosyl halides.

Infrared spectra of monomeric acetic acids [CH3COOH(D) and CD3COOH(D)] isolated in Ar and N2 matrices near 4°K are reported. A large anharmonic potential‐energy contribution is evident from the observed isotopic frequency shifts. It is proposed that this arises primarily from the double‐minimum potential‐energy curve for tunneling of the H atom between O atoms via the COH angle bending coordinate. In all cases, important coupling between the COH angle bending and C–O stretching coordinates is observed, with a strong addition of CD3 (umbrella) angle deformation in the case of CD3COOH. Exceptional matrix effects are observed for the coupled vibrations of the –OH molecules. A complete assignment is proposed for these acetic acids on the basis of the new data. As additional supporting evidence, the spectrum of matrix‐isolated CH3COF and of acetic acid vapor at low pressure and long path length are reported.

The infrared spectra of SbF5 and AsF5 suspended in argon and neon matrices have been recorded between 4000 and 100 cm−1. The spectra of SbF5 and AsF5 are radically different and show that monomeric SbF5 belongs to symmetry group C4υ rather than to group D3h. The spectral effects induced by forming solid SbF5 from the monomers are understood in terms of associations through Sb–F–Sb fluorine bridge bonds. The behavior is compared with that observed previously for SF4. No evidence for fluorine bridging occurs with AsF5.

Additional data supporting the nearly free rotation of the water molecule trapped in a rare‐gas lattice are presented. Ortho—para spin conversion is strongly induced by adding O2 to the matrix. A simple model is suggested which correlates the intensities observed for H2O, HDO, and D2O suspended in Ar, and which estimates the rate of nuclear spin conversion to within a factor of 5 or 10. The majority of the water molecules occupy substitutional sites in the lattice obtained by removing a single rare‐gas atom.Several sharp, intense lines are tentatively assigned to the H bonded OD stretch of HDO and D2O dimers in Ar. They contrast markedly with the corresponding broad band of the OH stretch.

Spectra of matrix-isolated trifluoroacetic acid species and matrix-isolated and solid trifluoroacetic anhydride are reported. Vibrational assignments are given for the CF3COOH and CF3COOD monomers, the i.r. active vibrations of (CF3COOH)2 and (CF3COOD)2 cyclic dimers, and (CF3CO)2O. The analysis suggests that a very low barrier hinders internal rotation of the CF3 group in the acids and also indicates the probable absence of an equilibrium plane of symmetry in the monomers. The truth of these statements hinges on the interpretation of the data for the nominal COH bending vibration. For CF3COOH monomer this band shows two components that are separated by ~15 cm−1, while CF3COOD monomer yields a single, sharp band that is red-shifted by a normal amount. These observations, coupled with the anomalous isotopic frequency behavior found for this vibration with acetic acid monomers [C.V. Berney, R.L. Redington and K.C. Lin, J. Chem. Phys.53, 1743 (1970)], reinforces the suggestion that a relatively low barrier hinders H atom transfer between the two O atoms via a coordinate that originates as COH angle bending.

The infrared spectra of matrix‐isolated ClF3, BrF3, and BrF5 have been investigated in the region from 800 to 33 cm−1. All six fundamentals have been observed in Ar and N2 matrices for ClF3 and BrF3, which are planar T‐shaped molecules, and most of them in a Ne matrix. The two lowest‐frequency fundamentals, which could not be separated in the gas‐phase spectra [H. Selig, H. H. Claassen, and J. H. Holloway, J. Chem. Phys. 52, 3517 (1970)] are clearly visible in the matrix‐isolation spectra. Both molecules show only small gas‐matrix frequency shifts, and multiplet structure for both molecules suspended in Ar matrices may be understood in terms of isotope and matrix site effects. Several absorption bands found at low matrix‐isolation ratios are attributed to dimers and a tentative partial vibrational assignment is presented. Similar dimer structures are assumed for both substances. The structure seems best represented with two F bridges formed using the long‐bond F atoms. The structure is favored by the x‐ray and NMR data. Re‐evaluation of the spectral data for SF4, and comparison with ClF3 suggests reversing the literature assignments of the antisymmetric axial and equatorial S–F stretching vibrations for the SF4 monomer. Then consistent experimental agreement between the closely related ClF3 and SF4 molecules ensues and analogous structures for the matrix‐isolated dimers follow. Considered as transient liquid‐state species, the dimers demonstrate a highly likely fluorine exchange mechanism involving an intermolecular transfer of the bridging F atoms that can account for the exchange of nonequivalent F atoms which is observed in the liquid state for these systems. The vibrational frequencies of ClF3, SF4, BrF3, and BrF5 are compared and force constants are calculated for ClF3 and BrF3.

Infrared spectra of LiF species suspended in solid Ne, O2, CO, and CH4 at liquid‐helium temperature have been obtained. The monomeric LiF frequency (in cm−1) is 869 in Ne, a doublet at 819–824 in O2, 787 in CH4, and a doublet at 710–725 in CO, compared to 895 cm−1 in the gas phase. Some of these values seem consistent with Linevsky's statement that the solvent shift in LiF is primarily of electrostatic origin. Electrostatic calculations were made for the rare‐gas matrices in order to observe the effects of asymmetric solute positions in the ideal lattice substitutional site and to test ideal lattice breakdown, or ``solvation'' of the monomeric LiF solute. For reasonable distance parameters, both types of calculation can account for most, or all, of the observed solvent shift. These simple calculations show ways to reduce the dispersive contributions to commonly observed values but likewise illustrate the presently unsatisfactory state of a genuine understanding of the LiF—matrix systems.

High‐resolution spectra of H2O, HDO, and D2O suspended in solid Ar have been observed in the range 4°—27°K. Evidence has been obtained for the rotation of these species in Ar matrices. The majority of the observed lines are found to be in very good agreement with low‐J transitions of the gas spectra, allowing for a small matrix shift. Transitions arising from both spin modifications of H2O and D2O have been observed and the observed intensities suggest that a large degree of spin equilibration has taken place. A small contamination of O2 may be responsible for this. A perturbation of one of the rotational levels of ν2—H2O is discussed.

The infrared spectrum of SF4 trapped in an argon matrix at ∼4°K shows characteristic changes when the sample is warmed to allow diffusion and recooled. These changes are discussed in terms of association of the SF4 molecules, and their simplicity and stability suggest a simple model for the dimer and more highly associated species. Weak bonding appears to exist between the pair of equatorial F atoms on one SF4 molecule and the sulfur lone pair of electrons on an adjacent SF4 molecule. The spectrum of SOF2, present as an impurity, shows changes suggestive of the formation of an SF4–SOF2 complex. The observations, together with the NMR data of Muetterties and Phillips indicate that the mechanism for the rapid exchange of axial and equatorial fluorines in liquid SF4 at room temperature is not intermolecular. A low barrier for the inversion of isolated SF4 is also ruled out by the apparent absence of inversion effects in the microwave spectrum of the vapor, studied by Tolles and Gwinn. The conclusion is drawn that there are two possible paths for the dimerization or association reactions, and that one of these paths involves inversion of the SF4 molecule. The activation energy of the latter reaction corresponds closely to the inversion energy of SF4, which must be markedly smaller in this dimeric transition state than in an isolated SF4 molecule.