J. P. Perchard

Study of hydracids trapped in monatomic matrices. I. Near infrared spectra and aggregate structures

The infrared spectra of H35Cl, D35Cl, HBr, DBr and their mixtures in solid argon and krypton in the range 10–30 K are presented. Studies have been made over a wide concentration range, for matrix/hydracid ratio from 1000 to 20 which, together with annealing experiments and H/D isotopic dilutions, allow a complete discussion of polymeric species spectra. In the monomer region, Q features are clearly identified at low M/R ratio and assigned to lattice distortion effects on isolated molecules. A new assignment for dimer bands is proposed, in which the two molecules are not equivalent and characterized by different values of force constants and moment derivatives. The trimer is found cyclic, a configuration already mentioned, the three molecules being equivalent and oriented along the sides of an equilateral triangle. After annealing, a new polymeric species associated with a strong band at lower frequency appears and is identified, in the light of H/D mixture spectra, as a cyclic planar tetramer. From accura...

Infrared spectrum of the methanol dimer in matrices. Temperature and irradiation effects in solid nitrogen

Four different open chain forms of methanol dimer have been identified in nitrogen matrices through temperature and IR irradiation effects. Each form is characterized by two OH stretching vibration frequencies, one (D1) close to the monomer frequency (3664 cm−1) and corresponding to the oxygen perturbed (electron donor) oscillator, and the other (D2) around 3500 cm−1 due to the hydrogen perturbed oscillator. Concentration ratios between two of these species (A: 3655 and 3519 cm−1; B: 3651 and 3504 cm−1) depends reversibly on temperature: the A form is predominant below 8 K while the B form is mainly observed above 10 K; this thermal process is fast. Moreover, the A or B concentration increases by IR irradiation at the expense of the C and D forms (C: 3659 and 3496 cm−1; D: 3654 and 3489 cm−1). This photoisomerization leads to a steady state with predominance of A or B, according to the temperature: its rate, relatively slow, has been quantitatively compared for OH and OD methanols. Since these processes a...

Properties of the hydracids trapped in a nitrogen matrix: Experimental and static field approximation study

The properties of the hydracid monomers and dimers trapped in N2 matrices are studied through an experimental reinvestigation of the near and far infrared spectra. In the nir spectra, two kinds of dimers are identified: a nearest‐neighbor (nn) dimer in which the two molecules are nonequivalent and a next‐nearest‐neighbor (nnn) dimer giving rise to a specific absorption very close to the monomer signal. New data in the fir confirm the previous assignment of the librational modes of the monomer but do not allow the identification of the corresponding dimer bands. These results are interpreted according to intermolecular potential calculations, taking into account the angular distortion of the matrix molecules around the HX impurity. An analytical description of the orientation quantum states for the impurities is developed and conveniently explains the fir monomer data by the lifting of the symmetry properties of the perfect crystal. The theoretical frequencies are in much better agreement with experimental when the N2 crystal dynamics is included. In the same way, calculations performed on the dimers show they lose their entity properties in the N2 crystal. Moreover, the librational response of the (HX)2 species, found in the same frequency range as the monomer, may account for a surprising discrepancy between experimental and calculated fir monomer band intensity ratio. The results obtained in the nir lead to a crucial modification of the electric multipole derivatives with respect to the internuclear coordinate in the hydracid dimers, which is explained in terms of a charge transfer process between the two molecules.

Study of hydracids trapped in monatomic matrices. II. Intermolecular potential calculations of the structure and spectral response of polymers

Intermolecular potential calculations are developed for hydracids trapped in rare gas matrices and the results concerning both geometries and spectral responses of low polymers are compared to the analysis of experimental data previously described. Geometrical structures, including matrix distortion, are calculated from a minimization of the total energy. Cyclic and planar conformations found for trimers and tetramers satisfy both criteria: the (molecular) packing tendency imposed by the isotropic Lennard‐Jones potential and the highest order symmetry for this packing required by the electrostatic potential. In a second step, the corresponding librational and vibrational frequencies are calculated according to the usual techniques of separation of angular and vibrational variables. For librations, it is moreover possible to separate in‐plane and out‐of‐plane motions, the first ones lying at higher frequency than the second; intensities of the corresponding bands are also calculated, taking into account th...

Hydracid-dimethyl ether interactions in matrices: Part II. IR spectral properties of (CIH)n-dimethyl ether complexes with n = 1, 2, 3

Abstract Molecular complexes formed between hydrogen (deuterium) chloride and dimethyl ether trapped in Ne, Ar and N2 matrices have been studied by IR spectroscopy. Matrix spectra at low concentrations in DME (typically matrix/DME = 500) and variable concentrations in hydracid allow the identification of several species (CIH)n-DME, the structures of which are discussed. The spectral properties of the 1:1 complex are analysed in detail in the light of current theories on hydrogen bonding. The properties of the potential function of this system are revealed, the behaviour of which is unusual.

Why are perturbations of HCl by N2 and CO so different?: Part II. Matrix isolation experiments

Abstract The infrared and raman spectra of hydracids (HCl, DCl, H 35 Cl, D 35 Cl, HBr) codeposited with dopants P (CO, 13 CO, 13 C 18 O, N 2 ) in argon matrices are presented. Studies have been carried out over a wide concentration range, for matrix/dopant ratios from 1000 to 10 which, together with H D isotopic dilutions, allows identification of several (HX) m (P) n aggregates (P = CO, N 2 ) such as m = 1, n =1, 2, 3 (CO case), and m = 2, n = 1, 2 (CO and N 2 cases). The straightforward identification of the bands assignable to the HClue5f8CO codimer for six isotopic species allows an accurate force field calculation to be done. For the (HCl) 2 (P) n aggregates, intensity and frequency measurements are used for a comparison between the HCl molecules which are non-equivalent. From the whole data a comparison is drawn between the perturbing power of CO and N 2 ; this second molecule is a poorer electron donor than CO but is able, however, to destroy the HCl dimer structure. Finally, the relative stability of the various copolymers (HCl) m (P) n is discussed using the results of careful diffusion experiments. It is shown that stability generally increases with m and decreases with n .

The carbon dioxide–hydrogen chloride complexes. A matrix isolation study and an abinitio calculation on the 1–1 species

Vibrational (IR and Raman) spectra are reported for binary mixtures of H(D)Cl with CO2 in argon matrices at 10 K. At high dilution in both dopants the 1:1 complex is identified by three of its modes. In the presence of an excess of HCl with respect to CO2, a 2:1 complex (HCl)2CO2 with two non equivalent HCl molecules is evidenced. For CO2/HCl molar ratios larger than one a series of lines in the HCl region area characteristic of 1:n aggregates (n=2–4). Finally, for HCl/CO2 molar ratio of the order of one and Ar/HCl=500, two bands in the HCl region are believed to characterize the 2:2 species. For all of these complexes HCl vibrational perturbations are weak, all the bands being in the frequency range 2854–2790 cm−1. Base submolecule modes show small displacements towards high as well as low frequency, depending upon the structure of the complexes. Ab initio calculations on the 1:1 complex have been performed to obtain the equilibrium geometry, the hydrogen‐bond dissociation energy and the two first multip...

Characteristics of the OH(OD) bands of methanol and ethanol in lithium salt—alcohol mixtures: saturated solutions and crystals

Abstract Raman spectra of alcohol (methanol, ethanol)—lithium salt (LiCl, LiBr, LiClO 4 ) mixtures were examined. Results on OH stretching bands are presented for saturated solutions at room temperature and for crystals obtained by cooling these solutions. In this second case well defined compounds, of the hydrate type, give rise to very narrow bands, showing that the hydrogen atom positions are ordered. For the CH 3 OH—LiBr system, isotopic OH/OD dilutions lead to the conclusion of a coupling between four OH identical vibrators, probably surrounding one Br − anion.

Reinvestigation of the Raman spectra of dihydrogen trapped in rare gas solids. I. H2, HD, and D2 monomeric species

The vibration–rotation and pure rotational Raman spectra of H2, HD, and D2 trapped in Ar, Kr, and Xe matrices have been recorded at 9 K. The frequencies which have been measured within an accuracy of 0.3 cm−1 are compared to the results of recent calculations. Except for the S0(0) line of HD the agreement between observed and calculated matrix shifts is satisfactory. The anomalous blue shift observed for the S0(0) line of HD is well interpreted within the rotation translation coupling (RTC) framework.

Rare-gas oxide excimers in matrices

Abstract A model of interaction between low-lying electronic states of oxygen atoms and a host crystal has been designed to account for luminescence and chemiluminescence processes observed during far UV photolysis of oxygenated precursors in rare-gas matrices. A mechanism that involves different trapping sites (substitution in neon, insertion in argon, krypton and xenon) explains the observed features.