High-resolution infrared spectroscopy of isotopic impurity Q1(0) transitions in solid parahydrogen

Abstract

High resolution electronic spectroscopy of 1aminonaphthalene: S 0 and S 1 geometries and S 1←S 0 transition moment orientationsWe have made a high-resolution infrared spectroscopic study of the Q 1 (0) ͑vϭ1←0, Jϭ0←0͒ vibrational transitions of the isotopic impurities D 2 and HD in solid parahydrogen. Each impurity has a spectrum composed of ϳ100 sharp lines spread over ϳ0.4 cm Ϫ1 . The linewidths vary, but are on the order of 10 MHz. These spectra make clear: ͑1͒ the infrared Q 1 (0) transitions of Jϭ0 isotopic impurities are induced by the quadrupolar fields of nearby impurity Jϭ1 molecules; and ͑2͒ the spectral pattern of strong Q 1 (0) lines is due to the splitting of the M -orientational levels of Jϭ1/Jϭ0 o-D 2 or Jϭ1/Jϭ0 HD nearest-neighbor ͑nn͒ impurity pairs. With the aid of several theoretical works, the strong lines in the D 2 and HD spectra can be individually and unambiguously assigned as specific quantum state Q 1 (0) transitions of nn impurity pairs containing p-D 2 /o-D 2 or o-H 2 /o-D 2 , and o-H 2 /HD, respectively. The assigned transitions of nn impurity pairs containing o-H 2 are confirmed by combination differences which agree to within 5ϫ10 Ϫ4 cm Ϫ1 , the instrumental precision. These assignments yield complete Q 1 (0) energy level diagrams for the nn impurity pairs o-H 2 /o-D 2 and o-H 2 /HD embedded in solid parahydrogen. The experimental energy level splittings are fit to a two parameter model which describes anisotropic interactions in the parahydrogen crystal. These experimental parameters appear to have significant contributions from the changes in renormalization and lattice constant around the heavier isotopic impurity. We have also assigned a few of the weaker spectral features as Q 1 (0) transitions of more distant impurity pairs, but the bulk of these transitions are yet to be assigned. They do form a distinctive pattern and are thought to be the Q 1 (0) transitions of impurity triples and larger clusters. This study is one of the few cases for which high-resolution laser spectroscopy has been successfully applied to the condensed phase and for which many of the transitions have rigorous quantum state assignments.

Refractive index measurements of solid parahydrogen

“…With proper care in the crystal-growth process, however, a transparent single crystal always resulted. Previous work has established that high purity para-H 2 crystallizes to form a hexagonal close-packed lattice at low temperature and high pressure [15] and that the c axis follows the largest thermal gradient [4,17]; in the present case this is the vertical axis.…”

Matrix isolation spectroscopy of H2O, D2O, and HDO in solid parahydrogen

“…The use of pH2 solids with very low residual orthohydrogen (oH2) concentrations as matrix hosts for chemically interesting dopants originated in the Oka laboratory in Chicago, and has advanced in collaboration with Shida and Momose and coworkers in Kyoto (14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). These authors have reviewed in detail the unique properties of solid pH2 as amatrix host, including the preservation of the spherical nature of the ground state (v = 0, J = 0) pH 2 molecules in the solid phase, and the resulting advantages to high resolution rovibrational spectroscopy (14,16).…”

Tunneling chemical reactions in solid parahydrogen: Direct measurement of the rate constants of R+H2→RH+H (R=CD3,CD2H,CDH2,CH3) at 5 K

“…During the past decade we have been studying rovibrational spectra of molecules embedded in solid p-H 2 which has several salient features in both high resolution spectroscopic and in-situ photolytic studies. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] The p-H 2 matrix is capable of providing not only high resolution spectroscopic information regarding embedded molecules but also subtle intermolecular interaction between trapped molecules and the matrix hydrogen molecule. 12,13,[15][16][17][18]21,22 The feasibility of the study of in-situ photolysis stems from the fact that molecules in solid p-H 2 happen to be free from the cage effect, which allows us to study photolytically produced fragments such as radicals originating from the parent molecule.…”