Man-Chor Chan

Infrared spectroscopic study of rovibrational states of methane trapped in parahydrogen crystal

The ν3 and ν4 vibrational transitions of methane trapped in solid parahydrogen have been observed by using Fourier transform infrared and high resolution laser spectroscopy. The observed spectrum is interpreted in terms of rovibrational states of the spherical rotor which are subjected to the crystal field splitting. The ν4 band shows extremely sharp lines of a width of ∼0.003 cm−1, while the ν3 band exhibits broader lines of a width of 1 cm−1. The infrared selection rules derived from an extended group theory to take into account the field effect are consistent with the observed spectra. The intermolecular interaction and the field effect in solid parahydrogen are analyzed quantitatively.The ν3 and ν4 vibrational transitions of methane trapped in solid parahydrogen have been observed by using Fourier transform infrared and high resolution laser spectroscopy. The observed spectrum is interpreted in terms of rovibrational states of the spherical rotor which are subjected to the crystal field splitting. The ν4 band shows extremely sharp lines of a width of ∼0.003 cm−1, while the ν3 band exhibits broader lines of a width of 1 cm−1. The infrared selection rules derived from an extended group theory to take into account the field effect are consistent with the observed spectra. The intermolecular interaction and the field effect in solid parahydrogen are analyzed quantitatively.

Laser spectroscopic studies of the pure rotational U0(0) and W0(0) transitions of solid parahydrogen

High resolution spectrum of multipole-induced transitions of solid parahydrogen was recorded using diode and difference frequency laser spectroscopy. The J=4<--0 pure rotational U_0(0) transition observed in the diode spectrum agrees well in frequency with the value reported by Balasubramanian et al. [Phys. Rev. Lett. 47, 1277 (1981)] but we observed a spectral width smaller by about a factor of 4. The J=6<--0 W_0(0) transition was observed to be exceedingly sharp, with a width of ~70 MHz, using a difference frequency spectrometer with tone-burst modulation. This transition is composed of three components with varying relative intensity depending upon the direction of polarization of laser radiation. These components were interpreted as the splitting of the M levels in the J=6 state due to crystal field interactions. In addition, a new broad feature was found at 2452.4 cm^(−1) in the low resolution Fourier-transform infrared (FTIR) spectrum of solid hydrogen and was assigned to be the phonon branch W_R(0) transition of the W_0(0) line. The selection rules, crystal field splitting of J=4 and J=6 rotons, and the measured linewidth based on these observations are discussed.

High resolution infrared spectroscopy of deuterium in p‐H2 matrix

The high resolution spectrum of the fundamental band of deuterium impurity embedded in solid parahydrogen has been studied using a difference frequency laser spectrometer. This observation represents the first case of high resolution matrix spectroscopy in solid hydrogen. Both the Q1←0(0) and Q1←0(1) transitions were resolved into sharp features with a typical linewidth of ≲ 10 MHz, while both the S1←0(0) and S1←0(1) transitions appeared to be much broader with widths of ∼0.07 cm−1. A discussion of the linewidths based on homogeneous broadening is presented.

Observation of the U1←0(1) transition of solid deuterium

Infrared absorption in the 3 μm region of normal and ortho enriched solid deuterium samples at 4.2 K has been restudied with improved signal‐to‐noise ratio using a Bomem FTIR spectrometer. The zero‐phonon U1←0(1) transition of deuterium was observed for the first time in the spectrum of normal D2. In addition, we also observed the phonon branches UR(0) [of the U1←0(0) transition] and UR(1) [of the U1←0(1) transition], which were not seen in previous work. The analysis of the spectra and the effect of p‐D2 molecules on the intensities and linewidths of the transitions are discussed. The hexadecapole moment of the U1←0(0) transition was estimated to be 0.121 ea40 from the experimental integrated intensity.

Laser absorption spectroscopy of the d3Π(g) ← c3Σ(u)+ transition of C2.

High-resolution laser absorption spectroscopy using concentration modulation has been applied to record the near-infrared spectrum of C2 in an AC hollow-cathode discharge of acetylene/helium mixtures. The (2,1) and (1,0) vibronic bands of the d3Π(g)– c3Σ(u)+ system have been observed in the spectral region between 12,010 and 12,540 cm(–1). While the analysis of the (1,0) band was straightforward, the (2,1) band was found to be perturbed. Using the effective Hamiltonians for 3Π and 3Σ+ states, molecular constants for the vibrational levels of the c3Σ(u)+ state were retrieved in least-squares fits of the observed spectral lines. The experimental conditions, detailed analysis of the perturbations, and the determined molecular constants are reported.