arXiv subjects

M. L. Niu

Publications and source records attributed to M. L. Niu.

9 recordsLinked to original sources

arXiv2022

Fourier-transform spectroscopy of $^{13}$C$^{17}$O and deperturbation analysis of the A$^1Π$ ($ν$ = 0 - 3) levels

The high-resolution B$^1Σ^+$ - A$^1Π$ (0, 0) and (0, 3) emission bands of the less-abundant $^{13}$C$^{17}$O isotopologue have been investigated by Fourier-transform spectroscopy in the visible region using a Bruker IFS 125HR spectrometer at an accuracy 0.003 cm$^{-1}$. These spectra are combined with high-resolution photoabsorption measurements of the $^{13}$C$^{17}$O B$^1Σ^+$ $\leftarrow$ X$^1Σ^+$ (0, 0), B$^1Σ^+$ $\leftarrow$ X$^1Σ^+$ (1, 0) and C$^1Σ^+$ $\leftarrow$ X$^1Σ^+$ (0, 0) bands recorded with an accuracy of 0.01 cm$^{-1}$ using the vacuum ultraviolet Fourier-transform spectrometer, installed on the DESIRS beamline at the SOLEIL synchrotron. In the studied 17,950 - 22,500 cm$^{-1}$ and 86,800 - 92,100 cm$^{-1}$ regions, 480 transitions have been measured. These new experimental data were combined with data from the C $\to$ A and B $\to$ A systems, previously analyzed in 13C17O. The frequencies of 1003 transitions derived from 12 bands were used to analyze the perturbations between the A$^1Π$ ($ν$ = 0 - 3) levels and rovibrational levels of the d$^3Δ_i$, e$^3Σ^-$, a$'{}^3Σ^+$, I$^1Σ^-$ and D$^1Δ$ states as well as to a preliminary investigation of weak irregularities that appear in the B$^1Σ^+$ ($ν$ = 0) level. Deperturbed molecular constants and term values of the A$^1Π$ state were obtained. The spin-orbit and L-uncoupling interaction parameters as well as isotopologue-independent spin-orbit and rotation-electronic perturbation parameters were derived.

physics.chem-ph↗

arXiv2016

Precision measurements and test of molecular theory in highly-excited vibrational states of H$_2$ $(v=11)$

Accurate $EF{}^1Σ^+_g-X{}^1Σ^+_g$ transition energies in molecular hydrogen were determined for transitions originating from levels with highly-excited vibrational quantum number, $v=11$, in the ground electronic state. Doppler-free two-photon spectroscopy was applied on vibrationally excited H$_2^*$, produced via the photodissociation of H$_2$S, yielding transition frequencies with accuracies of $45$ MHz or $0.0015$ cm$^{-1}$. An important improvement is the enhanced detection efficiency by resonant excitation to autoionizing $7pπ$ electronic Rydberg states, resulting in narrow transitions due to reduced ac-Stark effects. Using known $EF$ level energies, the level energies of $X(v=11, J=1,3-5)$ states are derived with accuracies of typically 0.002 cm$^{-1}$. These experimental values are in excellent agreement with, and are more accurate than the results obtained from the most advanced ab initio molecular theory calculations including relativistic and QED contributions.

physics.atom-ph↗

arXiv2016

Spectroscopy and perturbation analysis of the A$^1Π$(v=0) state of $^{13}$C$^{16}$O

The lowest $v=0$ level of the A$^1Π$, state of the $^{13}$C$^{16}$O isotopologue of carbon monoxide has been reinvestigated with a variety of high resolution spectroscopic techniques. The A$^1Π-$X$^1Σ^+(0,0)$ band has been studied by vacuum-ultraviolet Fourier-transform absorption spectroscopy, using the SOLEIL synchrotron as a radiation source. Spectra were obtained under quasi-static gas conditions at liquid-nitrogen temperature, room temperature and at an elevated temperature of 900 K, with absolute accuracies of 0.01$-$0.03 cm$^{-1}$. Two-photon Doppler-free laser spectroscopy has been applied to a limited number of transitions in the A$^1Π-$X$^1Σ^+(0,0)$ band, under collision-free circumstances of a molecular beam, yielding an absolute accuracy of 0.002 cm$^{-1}$. The third technique is high-resolution Fourier-transform emission spectroscopy in the visible region applied to the B$^1Σ^+-$A$^1Π(0,0)$ band in a gas discharge, at an absolute accuracy of up to 0.003 cm$^{-1}$. With these methods rotational levels of A$^1Π(0)$ could be studied in both parity components up to a rotational quantum number of $J=46$. The frequencies of 397 transitions were used to analyse the perturbations between the A$^1Π(0)$ level by vibrational levels of the D$^1\!Δ$, e$^3Σ^-$, d$^3\!Δ$, and a$'^3Σ^+$ states.

physics.atom-ph↗

arXiv2016

Constraint on a cosmological variation in the proton-to-electron mass ratio from electronic CO absorption

Carbon monoxide (CO) absorption in the sub-damped Lyman-$α$ absorber at redshift $z_{abs} \simeq 2.69$, toward the background quasar SDSS J123714.60+064759.5 (J1237+0647), was investigated for the first time in order to search for a possible variation of the proton-to-electron mass ratio, $μ$, over a cosmological time-scale. The observations were performed with the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph with a signal-to-noise ratio of 40 per 2.5 kms$^{-1}$ per pixel at $\sim 5000$ Å. Thirteen CO vibrational bands in this absorber are detected: the A$^{1}Π$ - X$^{1}Σ^{+}$ ($ν'$,0) for $ν' = 0 - 8$, B$^{1}Σ^{+}$ - X$^{1}Σ^{+}$ (0,0), C$^{1}Σ^{+}$ - X$^{1}Σ^{+}$ (0,0), and E$^{1}Π$ - X$^{1}Σ^{+}$ (0,0) singlet-singlet bands and the d$^{3}Δ$ - X$^{1}Σ^{+}$ (5,0) singlet-triplet band. An updated database including the most precise molecular inputs needed for a $μ$-variation analysis is presented for rotational levels $J = 0 - 5$, consisting of transition wavelengths, oscillator strengths, natural lifetime damping parameters, and sensitivity coefficients to a variation of the proton-to-electron mass ratio. A comprehensive fitting method was used to fit all the CO bands at once and an independent constraint of $Δμ/μ= (0.7 \pm 1.6_{stat} \pm 0.5_{syst}) \times 10^{-5}$ was derived from CO only. A combined analysis using both molecular hydrogen and CO in the same J1237+0647 absorber returned a final constraint on the relative variation of $Δμ/μ= (-5.6 \pm 5.6_{stat} \pm 3.1_{syst}) \times 10^{-6}$, which is consistent with no variation over a look-back time of $\sim 11.4$ Gyrs.

astro-ph.CO↗

arXiv2015

Spectroscopy and perturbation analysis of the CO A$^1Π-$X$^1Σ^+$ (2,0), (3,0) and (4,0) bands

The (2,0) (3,0) and (4,0) bands of the A$^1Π-$X$^1Σ^+$ system of $^{12}$C$^{16}$O have been re-investigated by high-resolution vacuum ultraviolet absorption spectroscopy. A VUV Fourier-transform spectrometer, illuminated by synchrotron radiation, was applied to record a jet-cooled spectrum, a room temperature static gas spectrum and a high temperature (900 K) quasi-static gas spectrum, resulting in absolute accuracies of 0.01$-$0.02 cm$^{-1}$ for the rotational line frequencies. Precise laser-based data were included in the analysis allowing for a highly accurate determination of band origins. Rotational levels up to $J=52$ were observed. The data were used to perform an improved analysis of the perturbations in the A$^1Π$, $v=2$, $v=3$, and $v=4$ levels by vibrational levels of the D$^1Δ$, I$^1Σ^-$, e$^3Σ^-$, d$^3Δ$, and a$'^3Σ^+$ states.

physics.atom-ph↗

arXiv2015

Test of quantum chemistry in vibrationally-hot hydrogen molecules

Precision measurements are performed on highly excited vibrational quantum states of molecular hydrogen. The $v=12, J=0-3$ rovibrational levels of H$_2$ ($X^1Σ_g^+$), lying only $2000$ cm$^{-1}$ below the first dissociation limit, were populated by photodissociation of H$_2$S and their level energies were accurately determined by two-photon Doppler-free spectroscopy. A comparison between the experimental results on $v=12$ level energies with the best \textit{ab initio} calculations shows good agreement, where the present experimental accuracy of $3.5 \times10^{-3}$ cm$^{-1}$ is more precise than theory, hence providing a gateway to further test theoretical advances in this benchmark quantum system.

physics.atom-ph↗

arXiv2015

High-precision laser spectroscopy of the CO A$^1Π$ - X$^1Σ^+$ (2,0), (3,0) and (4,0) bands

High-precision two-photon Doppler-free frequency measurements have been performed on the CO A$^1Π$ - X$^1Σ^+$ fourth-positive system (2,0), (3,0), and (4,0) bands. Absolute frequencies of forty-three transitions, for rotational quantum numbers up to $J = 5$, have been determined at an accuracy of $1.6\times10^{-3}$ cm$^{-1}$, using advanced techniques of two-color 2+1' resonance-enhanced multi-photon ionization, Sagnac interferometry, frequency-chirp analysis on the laser pulses, and correction for AC-Stark shifts. The accurate transition frequencies of the CO A$^1Π$ - X$^1Σ^+$ system are of relevance for comparison with astronomical data in the search for possible drifts of fundamental constants in the early universe. The present accuracies in laboratory wavelengths of $Δλ/λ= 2 \times 10^{-8}$ may be considered exact for the purpose of such comparisons.

physics.atom-ph↗

arXiv2014

Precision spectroscopy of the $X\,^{1}Σ_{g}^{+}, v=0\rightarrow 1$ ($J=0-2$) rovibrational splittings in H$_{2}$, HD and D$_{2}$

Accurate experimental values for the vibrational ground tone or fundamental vibrational energy splitting of H$_2$, HD, and D$_2$ are presented. Absolute accuracies of $2\times10^{-4}$ cm$^{-1}$ are obtained from Doppler-free laser spectroscopy applied in a collisionless environment. The vibrational splitting frequencies are derived from the combination difference between separate electronic excitations from the $X^{1}Σ_{g}^{+}, v=0, J$ and $v=1, J$ vibrational states to a common $EF^{1}Σ^{+}_{g}, v=0, J$ state. The present work on rotational quantum states $J=1,2$ extends the results reported by Dickenson et al. on $J=0$ [Phys. Rev. Lett. 110 (2013) 193601]. The experimental procedures leading to this high accuracy are discussed in detail. A comparison is made with full \emph{ab initio} calculations encompassing Born-Oppenheimer energies, adiabatic and non-adiabatic corrections, as well as relativistic corrections and QED-contributions. The present agreement between the experimental results and the calculations provides a stringent test on the application of quantum electrodynamics in molecules. Furthermore, the combined experimental-theoretical uncertainty can be interpreted to provide bounds to new interactions beyond the Standard Model of Physics or fifth forces between hadrons.

physics.atom-ph↗

arXiv2012

The CO A-X System for Constraining Cosmological Drift of the Proton-Electron Mass Ratio

The $\textrm{A}^1Π-\textrm{X}^1Σ^+$ band system of carbon monoxide, which has been detected in six highly redshifted galaxies ($z=1.6-2.7$), is identified as a novel probe method to search for possible variations of the proton-electron mass ratio ($μ$) on cosmological time scales. Laboratory wavelengths of the spectral lines of the A-X ($v$,0) bands for $v=0-9$ have been determined at an accuracy of $Δλ/λ=1.5 \times 10^{-7}$ through VUV Fourier-transform absorption spectroscopy, providing a comprehensive and accurate zero-redshift data set. For the (0,0) and (1,0) bands, two-photon Doppler-free laser spectroscopy has been applied at the $3 \times 10^{-8}$ accuracy level, verifying the absorption data. Sensitivity coefficients $K_μ$ for a varying $μ$ have been calculated for the CO A-X bands, so that an operational method results to search for $μ$-variation.

physics.atom-ph↗