Yangqin Chen

Optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy: A sensitive absorption-based scheme for paramagnetic molecular ions

The sensitivity of velocity modulation spectroscopy (VMS) has been greatly improved by use of the frequency modulation enhanced magnetic rotation spectroscopic (FM-MRS) technique. This technique, which we refer to as optical heterodyne magnetic rotation enhanced VMS, has been described in detail in this article, including the experimental configuration, a discussion of line shape, and a systematic analysis of its sensitivity. N2+ has been used as a test sample of the technique, and the observed absorption spectrum of H2O+ in the visible region of 16 680–17 300 cm−1 further confirmed the significant improvement of the sensitivity by this VMS technique.

Optical heterodyne detected velocity modulation molecular ionic spectroscopy

Optical heterodyne detected velocity modulation molecular ionic spectroscopy is presented and employed to observe the rovibrantional spectra of O2+ and O2-. That the lineshape of OH-VMS is of the second derivative of Gaussian profile and its sensitivity is 3.5 × 10−8 are theoretically analyzed, and they are both in good agreement with our experimental results.

Study on the (1, 2) and (2, 3) bands in the comet-tail system of 12C16O+ by optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy

Optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy was employed to observe the absorption spectra of the (1, 2) and (2, 3) bands of the comet-tail (A2 Πi—X2Σ+) system of CO+ in the visible region. A rotational analysis was performed to obtain more precise molecular constants for the four involved vibrational levels. Moreover, accurate RKR potentials and the Franck-Condon factors are given for these four vibronic levels. This calclulation reveals that v = 0, 5, 10 vibrational levels in the A state will be perturbed by the v = 10, 14, 18 levels in the × state, respectively, and the v = 9 level might be weakly perturbed by the v = 17 level.

Perturbation analysis of the υ = 6 level in the d3Δ state of CS based on its near-infrared absorption spectrum.

The spectrum of CS was recorded in the region of 12,086-12,630 cm(-1) by employing optical heterodyne concentration modulation laser absorption spectroscopy. Nearly 350 transitions were assigned to the (6, 0) band in the d(3)Δ-a(3)Π system of CS. The overtone transitions of the (12, 0) band in the a(3)Π(2)-a(3)Π(0) transition were first observed due to the perturbation interaction between d(3)Δ(1) and a(3)Π(2). The Λ doubling in the a(3)Π(1) state was also resolved at high rotational levels. The molecular constants of the a(3)Π (υ = 0) and d(3)Δ (υ = 6) levels and the perturbation parameters of the d(3)Δ (υ = 6) level were determined through nonlinear least-squares fitting using effective hamiltonians. The calculations of mixing fractions of the perturbed states were performed in order to obtain precise information on the perturbations of the d(3)Δ (υ = 6) levels. The mechanisms for perturbations of d(3)Δ (υ = 6) with the a(3)Π (υ = 12) and A(1)Π (υ = 1) levels, especially for the second-order perturbation, were discussed and explained according to first-order nondegenerate perturbation theory.

The absorption spectra of H2O+ and D2O+ in the visible and near infrared region

The absorption spectra of the electronic transition of H2O+ and D2O+ are investigated in the visible region from 16 400 to 17 600 cm−1 and in the near infrared region from 12 200 to 14 000 cm−1 using optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy (OH-MR-VMS). Three subbands including 111 spectral lines of H2O+ and seven subbands including 209 spectral lines of D2O+ are observed and analysed, among which four subbands, Σ (0,9,0)−(0,0,0), Δ (0,9,0)–(0,0,0), Π (0,8,0)–(0,0,0) and Π (0,10,0)–(0,0,0) of D2O+ in the near infrared region are studied for the first time. Holding the molecular constants of the lower state fixed at the published values, a set of molecular constants and rotational energy terms for each observed vibronic level of the upper state are obtained.

Concentration modulation laser spectroscopy of the C2 molecule Swan (d 3∏ g ←a 3∏ u ) system

Abstract The rotational structure of the C2 molecule Swan (d 3∏ g ←a 3∏ u ) system (0,1) band has been recorded by optical heterodyne magnetic rotation enhanced concentration modulation laser spectroscopy in the range of 17730–17880 cm−1. The C2 molecule is generated by an electric discharge through a mixture of acetylene and argon gas and a well-resolved spectrum is recorded with an absolute accuracy of 0.007 cm−1. Sensitivity of the method enables us to observe not only the traditionally observed branches of Δω = 0 sub-bands but also some Δω≠0 transitions, providing a slight improvement in the accuracy of some molecular constants of the two states. The theoretical spectra are simulated using the effective Hamiltonian of Brown and Merer and directly fitted to observed spectra; rotational parameters are derived from this fit for the two 3∏ states.

Study of (2, 0) Band of A2u - X2g+ System of N2+ by Optical Heterodyne Detected Velocity Modulation Spectroscopy

The (2, 0) band of the A2Πu-X2Σg+ system of N2 + was rotationally studied via optical heterodyne detected velocity modulation spectroscopy. Owing to the high sensitivity of the spectroscopy employed, the frequencies of 310 lines of this band were accurately determined. Moreover, those overlapped lines were also well determined via deconvolution method. A nonlinear least-squares fitting procedure using a standard Hamiltonian was applied to analyze this band. Therefore, the most accurate molecular constants were obtained.

Absorption Spectroscopy of (8,1) Band in d3Δ-a3Π System of CS Radical

The CS radical was generated by discharging the mixture gas of CS2 and Helium. The Doppler limited spectra of CS were recorded in the region of 12350–12950 cm−1 using optical heterodyne concentration modulation absorption spectroscopy. Three hundred and twenty-six lines were recorded and assigned to the d3Δ-a3Π (8,1) band, in which eighty-three transitions were first observed. A set of improved molecular constants for the d3Δ(v=8) and a3Π(v=1) levels were determined by a non-linear least-squares fitting of all the lines to the effective Hamiltonian.

Band (5, 0) in the Red System A2ΠI - X2Σ+ of CN Studied by Optical Heterodyne Magnetic Rotation Enhanced Concentration Modulation Spectroscopy

We study the CN radical using optical heterodyne magnetic rotation enhanced concentration modulation spectroscopy in the visible region. The radical has been produced in the ac glow discharge of acetonitrile with helium as the carrier gas. The (5, 0) band of the red system A(2)Pi(I) - X(2)Sigma(+) in the range 17450-17830cm(-1) has been observed and rotationally analysed. We determine a set of precise molecular constants for the v = 5 vibrational level of CN in the A(2)Pi(I) state.

Measurement of the absorption spectrum of H2O+ in the visible region

Together with the 74 lines belonging to (0,9,0)-(0,0,0) band, the high-resolution absorption spectrum of H2O+ Ã2A1 - X2B1 system was observed in the visible region of 16680–17300 cm−1 using optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy for the first time, which verifies the high sensitivity and high signal to noise ratio (S/N) of this technique.