High resolution infrared spectra of H2-Xe and D2-Xe van der Waals complexes

Spectra of weakly-bound hydrogen-xenon complexes are studied in equilibrium gas mixtures at relatively high spectral resolution (0.04 cm-1) using a long-path (112 m), low-temperature (140 K) absorption cell and a Fourier transform infrared spectrometer. The data cover the regions of the H 2 and D2 fundamental stretching vibrations in the mid-infrared (\u3bb 3c 2.4, 3.3 \u3bdm), and are greatly improved compared to the only previous observation. The results serve as a stringent experimental benchmark for testing theoretical hydrogen-xenon intermolecular potential energy models, as well as forming the basis for deriving an improved semi-empirical potential. \ua9 2013 Published by NRC Research Press.Peer reviewed: YesNRC publication: Ye

Infrared photochromism in a quantum crystal: Laser pumping and probing in solid para-H 2 doped with CH 3F

Solid para-H2 doped with CH3F at 1.8 K is studied in the n3 region ( 3c1040 cm 1) using a quantum cascade laser source. Residual ortho-H2 gives rise to distinct spectral features due to CH 3F(ortho- H 2)N clusters with N = 0, 1, 2, etc. The laser power ( 3c30 mW) is sufficient to significantly affect the sample, enabling novel photochromism experiments to be performed on a solid para-H 2 matrix-isolated sample. It is found that population can be reversibly transferred between the N = 1 line and satellite features close to the N = 0 line. \ua9 2011 the Owner Societies.Peer reviewed: YesNRC publication: Ye

High resolution quantum cascade laser studies of the 3 band of methyl fluoride in solid para-hydrogen

Spectra of solid para-H2 doped with CH3F at 1.8K are studied in the 3 region ( 3c1040 cm-1) using a quantum cascade laser source. As shown previously, residual ortho-H2 in the sample ( 3c1000 ppm) gives rise to distinct spectral features due to clusters of the form CH3F-(ortho-H2)N, with N = 0, 1, 2, 3, etc. Brief annealing at 7K is found to give narrower spectral lines ( 650.006 cm-1) than conventional (5K) annealing, and causes the N 3 and 4 lines to fragment into two or more components. The N 3 line is observed to be particularly stable and persistent. The N = 0 line (no ortho-H2 neighbors) is resolved into two closely spaced ( 480.007 cm-1) components which are assigned to the K = 0 and 1 states of CH3F rotating around its C3v symmetry axis (ortho- and para-CH 3F, respectively). Similar K-structure is also evident for other lines. Weak but persistent features (N 1/2 lines) are observed mid way between N 0 and 1. \ua9 2011 American Institute of Physics.Peer reviewed: YesNRC publication: Ye

Infrared spectra of the C 2H 2-(OCS) 2 van der Waals complex: Observation of a structure with C 2 symmetry

Infrared spectra of the C 2H 2-(OCS) 2 trimer are studied by means of direct infrared absorption spectroscopy. The van der Waals complexes are generated in a supersonic slit-jet apparatus and probed using a rapid-scan tunable diode laser in the region of the \u3bd 1 fundamental vibration of the OCS monomer. Two infrared bands are analyzed for the lowest energy isomer of the trimer, which has C 2 symmetry and is experimentally observed here for the first time. A relatively strong band centered at 2068.93 cm -1 is assigned as the out-of-phase vibrations of the pair of equivalent OCS monomers. This band is blue-shifted relative to the free OCS monomer but with a reduced shift as compared with the analogous vibration of the nonpolar OCS dimer. A weaker red-shifted band observed at 2049.64 cm -1 establishes the nonplanarity of the OCS dimer subunit within the trimer. Spectra for three isotopologues in addition to the normal form are used to help define an experimental structure, which agrees well with past and present semiempirical calculations. \ua9 2011 American Chemical Society.Peer reviewed: YesNRC publication: Ye

Infrared spectra of acetylene dimers and acetylene-nitrogen: (DCCD) 2, H-bonded DCCD-HCCH, and DCCD-NN in the 4.1 μm region

Infrared spectra of the weakly-bound T-shaped acetylene dimers DCCD-DCCD and DCCD-HCCH are studied in the region of the DCCD ν 3 fundamental (∼2440 cm -1) using a pulsed supersonic slit-jet expansion and a tunable diode laser probe. The K a = 0 ← 1 and 1 ← 0 subbands, corresponding to the vibration of the DCCD monomer at the "top" of the T, are analyzed. Compared to the analogous spectrum of HCCH-HCCH, the present results are much less perturbed. The tunneling splitting for (DCCD) 2 in the excited state is determined to be 141 MHz, a big reduction from the previously determined ground state value of 424 MHz. The dimer A rotational constants show a large apparent increase upon vibrational excitation, and we discuss whether this increase is real. The linear DCCD-NN complex is also observed as an impurity in the spectrum, and it too is found to be unperturbed, in contrast with HCCH-NN. © 2011 Elsevier Inc. All rights reserved