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The OSQAR photon regeneration experiment searches for pseudoscalar and scalar
axion-like particles by the method of "Light Shining Through a Wall", based on
the assumption that these weakly interacting sub-eV particles couple to two
photons to give rise to quantum oscillations with optical photons in strong
magnetic field. No excess of events has b...
Laser-based experiment OSQAR in CERN is aimed to the search of the
axions by two methods. The photon regeneration experiment is using two
LHC dipole magnets of the length 14.3 m and magnetic field 9.5 T
equipped with an optical barrier at the end of the first magnet. It
looks as light shining through the wall. No excess of events above the
backgrou...
Recent intensive theoretical and experimental studies highlight the
possibility of new fundamental particle physics beyond the standard model that
can be probed by sub-eV energy experiments. The OSQAR photon regeneration
experiment looks for Light Shining through a Wall (LSW) from the quantum
oscillation of optical photons into Weakly Interacting S...
We present new calculations of the branching ratios between the various electronic and isotopic photodissociation channels of ozone. Special emphasis is placed on the isotopic/isotopologue differences since the contribution of the ozone photodissociation to the oxygen isotope and ozone isotopologue enrichments or fractionations is important for atm...
Using the 31A' ab initio Potential Energy Surface (PES) of Ozone and the Multi Configuration Time Dependent Hartree (MCTDH) program for wavepacket propagation, we have determined numerous eigenstates of this state for six ozone isotopologues. These bound vibrational levels are the upper levels of the Huggins band which cover the range from 27,000 t...
The spectroscopy and predissociation of the 3A2(0 0 0) state of 18O3 are investigated from the analysis of the absorption spectrum of the 3A2(0 0 0)←X˜1A1(110) hot band recorded by high sensitivity cw-CRDS between 7600 and 7920 cm−1. The noise equivalent absorption of the recordings is on the order of 1×10−10 cm−1. Forty transitions could be rotati...
Recent intensive theoretical and experimental studies shed light on possible
new physics beyond the standard model of particle physics, which can be probed
with sub-eV energy experiments. In the second run of the OSQAR photon
regeneration experiment, which looks for the conversion of photon to axion (or
Axion-Like Particle), two spare superconducti...
The very weak absorption spectra of 18O3 and 16O3 have been recorded between 7700 and 7920 cm−1 by high sensitivity cavity ring down spectroscopy (αmin ∼10−10 cm−1). The upper limit of the investigated region is only 6% below the dissociation energy. The spectrum consists in the superposition of very weak vibrational bands and unexpected broad abso...
The absorption cross sections of 18 isotopologues of the ozone molecule have been calculated in the range of the Hartley-Huggins bands (27000-55000 cm(-1)). All 18 possible ozone isotopologues made with (16)O, (17)O, and (18)O have been considered, with emphasis on those of geophysics interest like (16)O(3) (17)O(16)O(2), (16)O(17)O(16)O, (18)O(16)...
The absorption cross sections (XSs) of eighteen isotopologues of the ozone molecule have been calculated in the range of the Chappuis-Huggins-Hartley bands: 15000-55000 cm-1 with special emphasis to those of atmospheric interest: symmetric 16O3, 16O17O16O, and 16O18O16O and asymmetric 17O16O2 and 18O16O2. We have used the MCTDH code which is based...
This chapter introduces a new analytic form of the Absorption (Abs.). The “standard” reflection model is improved by taking into account the curvature of the upper state potential (in addition to its slope). It takes into account the quantum character of the final state by replacing the Dirac function by an Airy function. The model is adapted and a...
A new method to amplify the photon-axion conversions in a magnetic field is proposed using a buffer gas at a specific pressure in a photon-regeneration experiment. As a first result, new bounds for mass and coupling constant for laboratory experiments aiming to detect any hypothetical scalars and pseudoscalars, which can couple to photons were obta...
A new method to amplify the photon-axion conversions in magnetic field is proposed using a buffer gas at a specific pressure. As a first result, new bounds for mass and coupling constant for purely laboratory experiments aiming to detect any hypothetical scalars and pseudo-scalars which can couple to photons were obtained at 95% confidence level, e...
In the first paragraph, OSQAR foremost achievements are summarised together with a brief reminder of its scientific context. In the second paragraph, activities planned for 2008 are briefly reviewed including the expected scientific results. The third paragraph is devoted to the requests addressed to CERN as the host laboratory and as a collaborati...
The time gated laser induced fluorescence (LIF) excitation spectrum of adiabatically cooled 15N16O2 has been measured close to the dissociation limit (22 700–24 050 cm−1). The spectrum consists of numerous rotationally resolved vibronic bands with mainly irregular structures and consequently only an angular momentum labeling has been possible. Thes...
The 11 800–14 380 cm−1 frequency range has been scanned for rotationally resolved rovibronic transitions in the A2B2–X2A1 electronic band system of the symmetric (C2v) 16O14N16O and 18O14N18O isotopologues and in the corresponding electronic band system of the asymmetric (Cs) 18O14N16O isotopologue. The rotational analysis—reflecting minor differen...
More than 250 rotationally resolved vibrational bands of the A2B2 X2A1 electronic transition of 15NO2 have been observed in the 14 300 18 000 cm-1 range. The bands have been recorded in a recently constructed setup designed for high resolution spectroscopy of jet cooled molecules by combining time gated fluorescence spectroscopy and molecular beam...
We have measured the rovibronic densities of four symmetric (C2v) and two asymmetric (Cs) isotopologues of nitrogen dioxide just below their photodissociation threshold. At dissociation threshold and under jet conditions the laser-induced fluorescence abruptly disappears because the dissociation into NO(2pi(1/2)) + O(3P2) is much faster than the ra...
We have measured the rotationless photodissociation threshold of six isotopologues of NO2 containing 14N, 15N, 16O, and 18O isotopes using laser induced fluorescence detection and jet cooled NO2 (to avoid rotational congestion). For each isotopologue, the spectrum is very dense below the dissociation energy while fluorescence disappears abruptly ab...
A spectroscopic setup designed for high resolution spectroscopy of jet cooled molecules is described. The primary features of the new setup are an exceedingly low gas consumption and a high detection efficiency, which are achieved by optimizing the detection geometry of the time gated fluorescence in combination with a special piezo valve. This mak...
We have measured the dissociation threshold energy, $D_{0}, (NO_{2} + h\nu \to NO(^{2}\Pi_{1/2})+O(^{3}P_{2}))$ of the six $NO_{2}$ isotopologues made with $^{14}N$ or $^{15}N$ and $^{16}O$ or $^{18}O$ isotopes. These $NO_{2}$ isotopologues are cooled in a Helium supersonic jet at $T_{rot} \approx 2K$. For each isotopologue, the very dense set of b...
We propose an efficient method for calculating the eigenstates and adjusting the parameters of an effective Hamiltonian, which reproduces the experimentally observed energy levels of NO2 up to 11 800 cm−1 above the quantum mechanical ground state, that is a few thousands of cm−1 above the X 2A1–A 2B2 conical intersection, with a rms error less than...
Using intracavity laser absorption spectroscopy combined with a supersonic slit jet, we have observed and analyzed seven vibronic cold bands of NO2 between 10 800 and 11 680 cm−1. The vibronic energies, relative intensities, A, B, and C rotational constants, and the spin-rotation constants have been determined. The rotational constants play a cruci...
The most recent theoretical treatment of mass independent fractionation in ozone by Marcus, Hawthorn and Gao is based on RRKM unimolecular dynamics. The proposed mechanism for mass impendent fractionations is a slightly non statistical behavior of the vibronic eigenstates for the symmetric isotopomer and a statistical behavior for the asymmetric is...
The experimentally known vibronic energy levels of NO2 [J. Chem. Phys. 108 (1998) 6638] have been reanalyzed to determine the strength of the electronic coupling at the conical intersection between the ground X2A1 and excited A2B2 electronic states. The full set of vibronic levels located below were included in our analysis, i.e., 276 vibrational l...
We report the laser induced dispersed fluorescence spectra (LIDFS) of NO2 recorded when exciting 107 vibronic levels lying between 11 961 and 17 627 cm−1. These levels result from the vibronic interactions between the highly excited vibrational levels of the electronic ground state, 2A1, and the isoenergetic levels of the electronic excited state,...
More than 1700 rovibronic states of low angular momentum (J
= 1/2–7/2) have been observed by laser induced fluorescence (LIF) at high precision and resolution, ≃0.004 cm−1, in a range covering 133 cm−1 below the NO2 lowest photodissociation threshold D0. This allowed us to significantly improve and complete previous experimental
results devoted to...
This work is aimed at extending recent studies dealing with the highly excited vibrational dynamics of HOCl [J. Chem. Phys. 111, 6807 (1999); J. Chem. Phys. 112, 77 (2000)], by taking advantage of the fact that the OH-stretch remains largely decoupled from the two other degrees of freedom up to and above the dissociation threshold. The molecule is...
We use infrared-visible double resonance overtone excitation to promote HOCl molecules to single, well-characterized rotational levels of high OH stretching states just above the $HOCl \to HO + Cl$ dissociation threshold on the ground potential energy surface. Double resonance spectra are monitored by laser induced fluorescence (LIF) detection of t...
The Cavity Ring Down Spectroscopy (CRDS) technique is a unique tool for probing non fluorescing absorbing molecular, species. High resolution in achievable in the blue-UV energy region by intracavity frequency doubling a CW laser source (here a Ti:Sa) and by using a seeded supersonic jet (slit nozzle) expansion. The $NO_{2}$ radical is known to str...
By combining (be capabilities of a high-Q optical cavity with the ones of a supersonic jet (nozzle) expansion, we can get a powerful tool for probing weak absorbing molecular transitions or traces of contaminants ($\lambda \sim 5.10^{-10}/cm$). Moreover, sensitive high resolution spectroscopy is obtained by combining the Cavity Ring Down Spectrosco...
We use infrared-visible double resonance overtone excitation to prepare HOCl molecules in single, well-characterized rotational levels of high OH stretching states just above the dissociation threshold on the ground potential energy surface. Combined with time-resolved laser induced fluorescence (LIF) detection of the OH product, this approach allo...
We have analyzed the vibrational energies and wave functions of HOCl obtained from previous ab initio calculations [J. Chem. Phys. 109, 2662 (1998); 109, 10273 (1998)]. Up to approximately 13 000 cm-1, the normal modes are nearly decoupled, so that the analysis is straightforward with a Dunham model. In contrast, above 13 000 cm-1 the Dunham model...
We use infrared-visible double resonance overtone excitation to promote HOCl molecules to single, well-characterized rotational levels of high OH stretching states just above the HOCl-->HO+Cl dissociation threshold on the ground potential energy surface. Double resonance spectra are monitored by laser induced fluorescence detection of the OH dissoc...
Following our previous LIF [J. Chem. Phys. 95, 5701, (1991) and 103, 1732 (1995)] and ICLAS [Chem. Phys. 190, 207 (1995)] studies on NO2, we observed by LIF the NO2 vibronic levels between 11 680 and 13 900 cm−1. These observations allow us to characterize the vibronic levels resulting from the conical intersection between the X 2A1 and A 2B2 elect...
A new method of high resolution cavity ringdown spectroscopy (CRDS) was recently developed in our laboratory, where a narrow line, continuous wave (CW) single-frequency laser is used instead of a pulsed laser. Here, we will first discuss the main differences between the `traditional' pulsed CRDS and CW-CRDS. Then, we will describe our results explo...
Fourier-transform absorption spectra of NO2 at 298 K were recorded between 9000–15 000 cm−1 at Doppler-limited resolution (0.012 cm−1), in the region near the 2B2– 2A1 conical intersection. The strong rovibronic bands are rather isolated and organized into polyads which can be assigned by the number of bending quanta of the 2B2 state, corresponding...
We report experimental results concerning the laser-induced fluorescence (LIF) spectrum and the laser-induced dispersed fluorescence (LIDF) spectrum of NO2 recorded by exciting very loosely bound levels located just below the dissociation threshold D0 at 25128.57 cm−1 (NO2→NO(2Π1/2)+O(3P2)). We had already mentioned (R. Jost, J. Nygard, A. Pasinski...
The potential energy surfaces of the three low lying electronic states of NO2, namely the 2A1, 2B2, and 2B1 states, and the transition dipole moment surfaces between the ground state and both excited states have been calculated at two levels of ab initio theory; complete active space self-consistent field (CASSCF) and internally contracted multiref...
The rotationally resolved absorption spectrum of two bands of the oxygen dimer near 630 and 578 nm have been recorded by intracavity laser absorption spectroscopy both in a supersonic slit expansion of pure O2 and in a cell cooled at 77 K. These bands correspond to the transitions [O2(1Δg)v=0]2←[O2(3Σg−)v=0]2 and [O2(1Δg)v=0–O2(1Δg)v=1]←[O2(3Σg−)v=...
Following our previous laser induced dispersed fluorescence (LIDFS) study on NO2 [J. Chem. Phys. 95, 5686 (1991)], we observed the vibronic levels up to 13 900 cm−1 by LIDFS. These observations allow one to characterize the effect of the conical intersection between the X 2A1 and A 2B2 electronic potential energy surfaces (PESs). This effect has be...
Double-resonance overtone excitation prepares HOCl molecules in single rovibrational states above the unimolecular dissociation threshold in the ground electronic state. Detecting the OH dissociation fragments allows us to observe which reactant states lie above or below the dissocation threshold and determine that threshold to be 19 290.3±0.6 cm−1...
Presented in this text is a compilation of existing absorption cross sections of NO2, mainly at room temperature but also at lower and higher temperatures, with a quantitative comparison of their cross sections and wavelength calibrations. From this, we concatenate three selected cross sections (slightly corrected) in order to cover the widest poss...
This is the first experimental observation of the control of the dissociation energy of a polyatomic molecule with an external magnetic field. We have observed by laser-induced fluorescence that the NO2 photodissociation threshold is linearly lowered by a magnetic field. This effect reaches 13.2 cm-1 under 14 T, i.e., 2muBB. This result demonstrate...
We present an application of the level dynamics concept to a quantitative analysis of rovibronic interactions in NO,. The basic idea is to rake benefit of the paramagnetic character of the NO2 molecule (23 e(-)) in order to use a magnetic field as an external control parameter. We summarize first the relevant properties of the NO2 molecule like the...
The strong vibronic interactions between the A and X electronic states lead to a complex structure of the $NO_{2}$ spectrum in the visible and near-IR. The log-wavelength tail of the spectrum is very weak due to small Franck-Condon factors. In 1965, Douglas and $Huber^{h}$ recorded the first low-resolution spectra of the $NO_{2}$ bands in the near...
The NO2 photodissociation threshold has been observed by laser induced fluorescence in a jet at 25 128.57±0.05 cm−1. The unexpected high vibronic level density of 2.7 levels/cm−1 is tentatively attributed to long range interactions between the NO (2Π1/2) and O(3P2) products. The energy spacing and intensity distributions indicate rovibronic chaos....
The lowest photodissociation threshold of $NO_{2}$, located at 25128.57$\times$$0.05 cm^{-1}$, is now well characterized: below the threshold, the highly excited vibronic levels of $NO_{2}$, observed by LIF in a jet, have a lifetime of a few $10^{2}$ sec; above the threshold, the resonant levels have a liftime shorter than $10^{2}$ psec and no fluo...
The $C_{2}$ potential energy surfaces of the $X^{2}A_{1}$, $A^{2}B_{2}$ and $B^{2}B_{1}$ states of $NO_{2}$ are calculated at a high level of theory (CASSCF/CMRCI/cc-pVTZ), together with the corresponding dipole moment surfaces for the transitions X-A and X-B. All surfaces are fitted to a quadratic polynomial form in the symmetric stretching and be...
A new supersonic expansion made of several, up to 31 aligned nozzles, on top of a set of powerful Roots blowers has been built. Adequate optics allowed the recording of infrared absorption spectra in a cell with a Fourier transform interferometer, at high spectral resolution. The system was tested with N2O, between 2000 and 4800 cm−1. The ν1 + 2ν2...
We have recorded the high resolution (150 MHz) excitation spectra of NO2 molecules cooled in a supersonic jet in two energy ranges: 16 000–19 362 cm−1 [‘‘yellow’’ range, see R. Georges, A. Delon, and R. Jost, J. Chem. Phys. 103, 1732 (1995), hereafter referred to as paper I] and 23 326–23 945 cm−1 (‘‘blue’’ range). In this paper we are interested m...
We have measured the effective spin rotation constant and the Landé factors of the N = 1, K = 0 rotational levels of 34 2B2 vibronic levels of NO2 located in the 16578–17842 cm−1 energy range in a sufficiently high magnetic field to uncouple electron spin from rotation. The spin rotation constants are randomly distributed around zero and the Landé...
We have observed a set of 350 2B2 vibronic levels of NO2 in the 16 000–19 360 cm−1 energy range by the laser induced fluorescence (LIF) technique combined with a supersonic jet. This work extends (i.e., a larger energy range) and improves (i.e., a better detection threshold) our previous study [J. Chem. Phys. 95, 5701 (1991)]. 42 new 2B2 vibronic l...
The third stretching overtone transition of jet cooled methane has been recorded between 11 170 and 11 315 cm−1 by intracavity laser absorption spectroscopy associated with a supersonic slit jet expansion. By varying the methane percentage seeded in the carrier gas, we have studied the evolution of the spectrum vs the rotational temperature. The ro...
We have combined the high sensitivity of the ICLAS technique with the rotational cooling effect of a slit jet expansion in order to observe and to understand the visible and near infrared NO2 spectrum. By this way, an equivalent absorption pathlength of several kilometers through rotationally cooled molecules has been achieved. Due to the vibronic...
An almost complete knowledge of the NO2 energy spectrum is now available, from the ground state up to the first limit of dissociation at 25 130 cm–1. This allows the determination, by Fourier transformation, of the dynamic behaviour of this molecule as a function of energy. We have used the windowed Fourier-transformation technique introduced by Jo...
The paper presents spectroscopic results obtained on NO2 molecules with the intracavity laser absorption spectroscopy (ICLAS) technique in which the gas sample was rotationally cooled in a supersonic slit jet. A dye laser was used to study the 12500-16100 cm-1 energy range in which 156 cold bands have been observed. They represent about 65% of the...
We have observed the Zeeman effect on N=1, K=0 rotational levels of seven vibronic levels of NO2 located between 17 438 and 17 842 cm−1. We have used a supersonic jet, (Trot≊4 K) located inside a 5 MW Bitter coil of 100 mm bore which allows magnetic field scans up to 8 T. CW monomode ring dye laser excitation allows a resolution of about 300 MHz li...
The intracavity Laser Absorption Spectroscopy (ICLAS) has been use to observe weak absorption of NO2 and CH4 cooled in a supersonic jet through a slit. By this method, the thermally congested spectrum of the molecules is drastically simplified and analysis becomes possible. On NO2 we report preliminary results in the 13 470 - 14 440 cm-1 energy ran...
Significant improvements have been obtained on measurements of the NO2 jet cooled excitation spectrum in the 16 300–18 502 cm−1 range, previously obtained by Smalley et al. [J. Chem. Phys. 63, 4977 (1975)], Persch et al. [Ber. Bunsenges. Phys. Chem. 92, 312 (1988)], and Hiraoka et al. [J. Mol. Spectrosc. 126, 427 (1987)]. The improvements concern f...
The laser induced dispersed fluorescence spectra (L.I.D.F.S.) of jet cooled NO2 molecules in emission from 11 different vibronic levels located between 22 006 and 23 625 cm−1 was recorded. The corresponding variety of Franck–Condon accesses has allowed the observation of the complete set of the 191 lowest vibrational levels of the 2A1 ground state,...
We have recorded Zeeman anticrossing (ZAC) spectra of gas phase acetylene (HCCH) in the 1Auν′3=0–3 (ν′3 i normal mode of the trans-bent excited electronic state), J=K=I=0 levels. The energy range thus sampled was from 42200 to 45300 cm−1 above the rotationless zero-point level of the 1Σg+ state. The magnetic field was scanned from 0 to and the ZAC...
Anticrossing and quantum beat spectroscopies (employing magnetic fields from zero to 8 Tesla = 80 kGauss, or electric fields of up to 113 kV/cm) have been used to study intramolecular interactions in the acetylene molecule. Both Zeeman and Stark activity occurs among the low-lying rovibrational levels of the first excited singlet electronic state $...
We have observed, measured, and assigned 264 vibrational levels of the electronic ground state of glyoxal (C2H2O2) by studying the dispersed fluorescence spectra of the molecule excited by a cw dye laser. The cooling effect of a supersonic expansion simplifies considerably the excitation spectrum and allows us to excite the rotationless level of ab...
The high-resolution rotational spectra of several S1 ← S0 vibrational transitions of glyoxal are obtained and analyzed. Undispersed fluorescence excitation spectra are obtained with a CW ring dye laser in a supersonic jet, providing a linewidth down to 100 MHz. Rotational constants and band origins are determined with an asymmetric rotator program....
The vibrational analysis of the S1 ← S0 spectra from 465 to 415 nm leads to the location of 49 S1 vibrational levels between 0 and 2000 cm−1 of vibrational excitation in S1. The origins of bands are determined after rotational analysis within 0.01 cm−1. Their assignments are deduced from the analysis of the dispersed fluorescence emitted by these l...
Collision-induced intersystem crossing in a glyoxal has been studied at room temperature: the presence of gate states participating in this process, i.e. of states presenting a large singlet-triplet mixing coefficient β2, has been shown unambiguously. Detailed study of isolated transitions in emission issued from one of such state compared to the s...
In paper VI of this series, we have made the statistical analysis of the singlet-triplet coupling matrix elements for ten NS = 0 singlet vibrational levels of glyoxal, without determining the triplet quantum numbers. In this paper we present the complete assignment (triplet rotational quantum numbers and vibrational symmetry) of each anticrossing o...
By laser excitation of the rotationless level (J = 0) of ten vibrational levels of the S1 (Au) state (00, 72, 51, 81, 6171, 41, 8172, 21, 8141 and 2172) of supersonic jet cooled glyoxal, we have obtained S1-T1 anticrossing spectra using the homogeneous, high magnetic field (0–8 T) of a Bitter coil. As explained previously, Vst is readily obtained f...
A pulsed, doubled, dye laser is used to excite individual lines in the $A {^{1}}A_{u}-X {^{1}}\Sigma_{g}{^{\ast}}$ (i.e. $S_{1}-S_{0}$) system. Lines occuring in vibrational bands with 1 to 4 quanta of trans-bending vibration have been studied. Quantum beats and anticrossing spectra enable natural lifetime limited resolution in measurements on indi...
We excite single rovibronic $S_{1}$ levels of the Glyoxal molecule (CHO CHO) with an $Ar^{+}$ pumped CW ring dye laser. The Glyoxal is cooled in a supersonic jet. We monitor unresolved fluorescence as a function of magnetic field up to 8 T (homogeneity $\delta B/B \sim 10^{-5}$ in $1 cm^{3}$). Anticrossing accurs when rotational levels of high vibr...
We have performed anticrossing experiments in high magnetic fields on several rotational and vibrational singlet levels of glyoxal in a supersonic jet. We show that by analysis of these experiments, we can determine rotational quantum numbers, vibrational symmetry and rotational constants of the triplet level most efficiently coupled to the singlet...
We set the theory for the position of double resonance signals near an anticrossing point. We use this theory to interpret our experimental results for anticrossings between the (K ≈ 6, J = 13) rotational level of the vibrationless 0° 1Au state of glyoxal and five sample rovibrational triplet levels, leading to very precise (up to a few 10−4 on rel...
We set the theory for the amplitude and widths of double resonance signals near an anticrossing. This theory is used to discuss the possibility of measuring singlet, triplet and coherence relaxation parameters in our experiments on anticrossings between the (K = 6, J = 13) rotational level of vibrationless 0° 1Au state of glyoxal and a sample rovib...
Summary Anticrossing experiments were performed on both cis and trans isomers of glyoxal. The comparison of the widths and intensities
of these signals confirms the predominance of indirect spin-orbit coupling and the assignment of the1
A
u−3
A
u coupling in glyoxal to the small-molecule weak-coupling limit.
Level anticrossing and a new optical-radiofrequency double resonance technique were applied to a study of the singlet—triplet interactions for single rotational levels of the vibrationless 1Au state of glyoxal. The density and spectral distribution of triplet rotational levels virtually coupled to the (K = 6, J = 13) and (K = 7, J = 35) singlet sta...
An investigation of the triplet 3d-complex of H2, the g(3d) Σg , i(3d)Πg, and j(3d)Δg states and the nearby h(3s)Σg state, has been undertaken. Approximately 50 g-factors have been measured by optical Zeeman spectroscopy, for the 3d levels for v = 0–3, N ⩽ 7. A concomitant calculation of the L-uncoupling effects and the corresponding eigenvectors i...
Le but de cet article est de présenter une nouvelle variante d'anticroisement et de la comparer aux autres méthodes qui permettent de déterminer la position relative des niveaux de multiplicité différente. L'accent est mis sur l'analyse de la formule qui donne le signal d'anti-croisement lorsque celui-ci est observé sur l'intensité lumineuse. L'ana...
The 3 1K, v=1 level of H2 has recently been interpreted as an adiabatic mixture of vibronic levels of the EF 1Σs+ and the GK 1Σg+ double minimum states, with currently undetermined nonadiabatic corrections. Anticrossing spectra, which are sensitive to these state mixings, have been observed for the 3 1K, v=1, N level and the (3d) 3Σg+, v=1, N level...
The 3 ¹K, v=1 level of Hâ has recently been interpreted as an adiabatic mixture of vibronic levels of the EF ¹..sigma../sub s//sup +/ and the GK ¹..sigma../sub g//sup +/ double minimum states, with currently undetermined nonadiabatic corrections. Anticrossing spectra, which are sensitive to these state mixings, have been observed for the 3 ¹K,...
Singlet-triplet anticrossing spectroscopy has been used to determine cross sections for collisional transfer of angular momentum within Rydberg states of He. The measured results disagree with expectations derived from previous work; they are relatively small and, unlike the geometric cross sections, are not strongly dependent on principal quantum...
The method of singlet-triplet anticrossing has been extended to the n /sup 1en-dash/D levels of /sup 4/He with n = 3, 4, and 5. We measure both the zero-field singlet-triplet separation with a higher accuracy than optical measurements, and the antisymmetric part of the spin-orbit coupling between singlet and triplet states. The agreement with many-...
The method of singlet-triplet anticrossing has been extended to the n1-3D levels of 4He with n=3, 4, and 5. We measure both the zero-field singlet-triplet separation with a higher accuracy than optical measurements, and the antisymmetric part of the spin-orbit coupling between singlet and triplet states. The agreement with many-body perturbation ca...
Anticrossings between the 3d 1Πg and the 3d 3Πg states of D2 have been used to determine the relative positions of singlet and triplet levels, and Te, T0 and the electronic isotope shift for the a 3Σ state. An ab initio calculation of the a 3Σ state differs from experiment by only 1 or 2 cm−1, a difference, however, that exceeds the experimental er...
Anticrossings between excited singlet and triplet levels of the He2 molecule have been observed. Measurements have been made on anticrossings which take place between the f (3d) 3Deltau and F (3d) 1Deltau states both in the v=0, N=2,3,4 and v=1, N=2 vibrational and rotational levels. Analysis of these results yields a new and more precise value for...
We show that the singlet-triplet separation of H2 must be
lowered by 157.7 +/- 0.2 cm-1 compared to the hitherto
accepted value of Dieke. We have used a new kind of "level anticrossing"
method in which the anticrossing is due to the coupling of a singlet and
a triplet state by spin-orbit or hyperfine Fermi contact interaction.
Experimental results obtained by Hanle and Bitter-Brossel effects on the N=1 and N=2 (v=0, 1, 2, and 3) levels of the (1s3p)3Πu state of the parahydrogen molecule excited by electron impact are presented. Resonances are found at the experimentally lowest possible frequencies (21-64 MHz) in a region where the N. S decoupling is nonexistent for the N...
In the preceding paper some of our results on the magnetic-resonance experiments performed at 64 MHz indicated a beginning of N·S decoupling on the N=1 (1s3p)3Πu state of H2 excited by electron impact. In the present paper we present further results on the resonance experiments performed at higher frequencies in order to determine the fine structur...
Results on the resonance experiments performed at higher frequencies in order to determine the
fine structure of this level are presented. The findings indicate that the energy separation between J=1 and
J=2 levels is 160�5 MHz and between J=1 and J=0 levels it is 2100�600 MHz, and in addition the former
exhibits a small dependence on the vibration...
The time gated laser induced fluorescence (LIF) excitation spectrum of adiabatically cooled 15 N 16 O 2 has been measured close to the dissociation limit (22 700–24 050 cm À1). The spectrum consists of numerous rotationally resolved vibronic bands with mainly irregular structures and consequently only an angular momentum labeling has been possible....
