Shui-Ming Hu

High resolution vibration-rotation spectrum of the D2O molecule in the region near the 2ν1 + ν2 + ν3 absorption band

The high resolution Fourier transform spectrum of the D20 (ν = ν1 + ν2/2 + ν3 = 3.5) polyad was analysed within the framework of the Hamiltonian model taking into account resonance interactions between the seven states (310), (211), (112), (013), (230), (131) and (032). Transitions belonging to the 2ν1 + ν2 + ν3, 3ν1 +ν2 and 3ν2 + 2ν3 bands were assigned in the experimentally recorded spectrum. This provided the possibility of obtaining spectroscopic parameters of the ‘visible’ states (211), (310) and (032) and of estimating the band centres, and the rotational and resonance interaction parameters of the ‘dark’ states (112) and (131).

39Ar detection at the 10(-16) isotopic abundance level with atom trap trace analysis.

Atom trap trace analysis, a laser-based atom counting method, has been applied to analyze atmospheric 39Ar (half-life=269  yr), a cosmogenic isotope with an isotopic abundance of 8×10(-16). In addition to the superior selectivity demonstrated in this work, the counting rate and efficiency of atom trap trace analysis have been improved by 2 orders of magnitude over prior results. The significant applications of this new analytical capability lie in radioisotope dating of ice and water samples and in the development of dark matter detectors.

The stretching vibrational overtone spectra of PH3: Local mode vibrational analysis, dipole moment surfaces from density functional theory and band intensities

The infrared spectra of PH3 molecule were recorded on a Bruker IFS 120HR Fourier transform spectrometer from 4000 to 9500 cm−1. The P–H stretching vibrational frequencies and intensities were derived from the experimental data. The Morse oscillator parameters De and α in the anharmonically coupled anharmonic oscillator local mode model were determined by the least-squares fitting with the observed vibrational band centers. The ab initio three-dimensional P–H stretching dipole moment surfaces were calculated by the density functional theory method. The dipole moment vectors were projected to three kinds of molecule-fixed reference systems. The corresponding dipole moment components were fitted to polynomial functions in terms of the P–H bond length displacements with the molecular symmetry taken into account. The absolute band intensities were obtained and then compared with the experimental data. The results showed that a proposed improved bond dipole model can predict the absolute band intensities within...

Ultrasensitive near-infrared cavity ring-down spectrometer for precise line profile measurement

A cavity ring-down (CRD) spectrometer is built with a continuous-wave Ti:sapphire ring laser. Using a pair of R approximately 0.999 95 high-reflective mirrors, the noise-equivalent minimum detectable absorption loss reaches 7 x 10(-11)/cm over the spectral range of 780-830 nm. A thermal-stabilized Fabry-Perot interferometer is applied to calibrate the CRD spectrum with an accuracy of 1 x 10(-4) cm(-1). The quantitative measurement is carried out for the line profile measurements of some overtone absorption lines of C(2)H(2) near 787 nm. Doppler determined line shape has been observed with milli-Torr acetylene gas in the ring-down cavity. The instrumental line width is estimated from the line profile fitting to be <1 x 10(-4) cm(-1). It demonstrates that the CRD spectrometer with extremely high sensitivity is also very suitable for quantitative measurements including precise line profile studies in the near-infrared.

Fourier-transform intra-cavity laser absorption spectroscopy of HOD νOD=5 overtone

The newly developed high resolution Fourier-transform intra-cavity laser absorption spectroscopy (FT-ICLAS) was utilized to record the νOD=5 stretching overtone of HOD at a resolution of 0.05 cm-1 in the region 12550–12900 cm-1. The spectrum was rotationally analysed and the spectroscopic parameters were derived from nonlinear least-squares fitting. Good agreement of the observed with the calculated energy levels was achieved.

Laser spectroscopy of NiI: Ground and low-lying electronic states

High-resolution laser-induced fluorescence spectrum of a jet-cooled NiI molecule has been recorded in the near infrared and visible regions. The NiI molecule was produced by reacting laser-ablated nickel atom and methyl iodide (CH3I). Three electronic states have been identified that include the X 2Δ5/2 and two low-lying [13.9] 2Π3/2 and [14.6] 2Δ5/2 excited states. Molecular transition bands (v′,0) of the [13.9] 2Π3/2−X 2Δ5/2 system with v′=0, 4–9, and the (v′,0) bands of the [14.6] 2Δ5/2−X 2Δ5/2 system with v′=0–6 were observed and analyzed. Spectra of isotopic molecules confirmed the assignment of vibrational quantum number of the observed bands. Least squares fit of rotational transition lines yielded accurate molecular constants for the states studied. The bond length r0 measured for the X 2Δ5/2 is 2.3479 A and the equilibrium bond length, re, for the [13.9] 2Π3/2 and [14.6] 2Δ5/2 are, respectively, 2.4834 and 2.5081 A. With the use of a molecular orbital energy level diagram, we have examined the el...

High-resolution Fourier-transform intra-cavity laser absorption spectroscopy : Application to 12C2H2 near 12300 cm-1

The capabilities of intra-cavity laser absorption spectroscopy associated with a high-resolution Fourier-transform spectrometer (FT-ICLAS) are investigated with a Ti:Sapphire laser. Weak absorption lines of atmospheric water were used to test the accuracy of absolute intensity measurements by FT-ICLAS leading to an excellent agreement (a few %) with the HITRAN data. The performances in terms of spectral resolution (0.028 cm � 1 ) and sensitivity (2� 10 � 9 cm � 1 ) are illustrated by the spectroscopic study of the overtone spectrum of 12 C2H2 between 12 250 and 12 400 cm � 1 which allowed for a significant improvement of recent cavity ring-down measurements. Among the three P–R bands rotationally analyzed, one is newly observed. The absolute intensity values of the bands are given. 2003 Elsevier Science B.V. All rights reserved.

Identification of alcohol conformers by Raman spectra in the C-H stretching region.

The spontaneous polarized Raman spectra of normal and deuterated alcohols (C2-C5) have been recorded in the C-H stretching region. In the isotropic Raman spectra, a doublet of -CαH stretching vibration is found for all alcohols at below 2900 cm(-1) and above 2950 cm(-1). By comparing the experimental and calculated spectra of various deuterated alcohols, the doublets are attributed to the -CαH stretching vibration of different conformers. For ethanol, the band observed at 2970 cm(-1) is assigned as the stretching vibration of -CαH in the Cα-O-H plane of the gauche-conformer, while the band at 2895 cm(-1) is contributed from both the -CαH2 symmetrical stretching vibration of the trans-conformer and the -CαH stretching vibration out of the Cα-O-H plane of the gauche-conformer. The population of gauche-conformer is estimated to be 54% in liquid ethanol. For the larger alcohols, the same assignments for the doublet are obtained, and the populations of gauche-conformers with plane carbon skeleton are found to be slightly larger than that of ethanol, which is consistent with results from molecular dynamics simulations.

Cavity ring-down spectroscopy of Doppler-broadened absorption line with sub-MHz absolute frequency accuracy

A continuous-wave cavity ring-down spectrometer has been built for precise determination of absolute frequencies of Doppler-broadened absorption lines. Using a thermo-stabilized Fabry-Pérot interferometer and Rb frequency references at the 780 nm and 795 nm, 0.1 - 0.6 MHz absolute frequency accuracy has been achieved in the 775-800 nm region. A water absorption line at 12579 cm(-1) is studied to test the performance of the spectrometer. The line position at zero-pressure limit is determined with an uncertainty of 0.3 MHz (relative accuracy of 0.8 × 10(-9)).

Thermal beam of metastable krypton atoms produced by optical excitation

A room-temperature beam of krypton atoms in the metastable 5s[3/2]2 level is demonstrated via an optical excitation method. A Kr-discharge lamp is used to produce vacuum ultraviolet photons at 124 nm for the first-step excitation from the ground level 4p6 1S0 to the 5s[3/2]1 level. An 819 nm Ti:sapphire laser is used for the second-step excitation from 5s[3/2]1 to 5s[3/2]2 followed by a spontaneous decay to the 5s[3/2]2 metastable level. A metastable atomic beam with an angular flux density of 3 x 10(14) s(-1) sr(-1) is achieved at the total gas flow rate of 0.01 cm3/s at STP (or 3 x 10(17) at./s). The dependences of the flux on the gas flow rate, laser power, and lamp parameters are investigated.