Stark Resonances Research Articles

Laser Stark spectroscopy with a wide Stark tuning range

Laser Stark spectra of molecules have been observed with a Stark field tuning range of up to 25 kV mm −1; this is two to three times wider than that used generally. High fields were obtained by using Stark plates separated by 0.2 mm. The ν 3-band transitions of the CH 3F molecule were observed to test the performance of this wide tuning system using 12CO 2 laser lines. It was found that almost all the low- J ( J≤6) transitions have one or more Stark resonances with one of the laser lines and that several components have resonances with neighboring two (sometimes three) laser lines. This wide tuning system was proved to be applicable to Doppler-free spectroscopy by the observation of Lamb dips for the ν 3-band transitions of CH 3F and for the ν 4, p P(3,3) transition of PH 3 whose A 1 A 2 doublet was resolved. Furthermore this system was applied, using CO 2 and N 2O lasers, to the observation of the low- J transitions of the 2 ν 2- ν 2 hot band of PH 3, and the effective molecular constants for the 2 ν 2 state of PH 3 were determined.

Transition dipole moment measurements for the υ 9 band of difluoromethane using Rabi oscillations

Using sub-Doppler molecular-beam CO 2 laser Stark spectroscopy, well-resolved Rabi oscillations have been observed in the 1 11 ← 1 10, M = 1 ← 1 and 1 11 ← 2 12, M = 1 ← 2 transitions of the υ 9 fundamental band of CH 2F 2. A least-squares analysis of the data has yielded a rotationless transition dipole moment of 0.34 ± 0.02 D for this band. This result is consistent with previous results and believed to be more accurate. Also, 12 new laser Stark resonances for this band have been observed in this study.

Comment on "Exact calculations of quasibound states of an isolated quantum well with uniform electric field: Quantum-well Stark resonance"

Comment on "Exact calculations of quasibound states of an isolated quantum well with uniform electric field: Quantum-well Stark resonance"

Geometric theory of Stark resonances in multielectron systems

In this paper we consider a class of many-body systems in a weak homogeneous electric field. This class includes atoms and molecules with infinitely heavy nuclei. It follows from one of the results of this paper and a result of [S 3] that the bound states of such systems in the absence of electric field turn into resonances (which we call the Stark resonances) as soon as the electric field is switched on. (The stability part of this result was earlier proven in [HeSi] (see also [Hu 2]) under an assumption of dilation analyticity.) The main result of this paper is exponential bounds on the width (and therefore the lower exponential bounds on the life-time) of the Stark resonances. These bounds are given in terms of the Stark instanton action. In contrast to the usual (one body) action the latter is not entirely classical but incorporates certain quantum data (like ionization energies). The bounds give a partial generalization to the many electron case of the well-known Oppenheimer formula for the hydrogen.

Sharp exponential bounds on resonances states and width of resonances

We prove sharp exponential bounds on resonance states for the shape (α-decay) and Stark resonances. We use these bounds to estimate the width of these resonances. The bound on width of Stark resonances gives a partial generalization of the classical Oppenheimer formula derived originally for the hydrogen atom.

Lifetime measurements of interference-narrowed sodium Stark resonances.

We report measurements of the temporal decay of sodium Stark resonances over regions of interference narrowing and compare with calculations using Wentzel-Kramers-Brillouin quantum-defect (WKB-QD) Stark theory. The measurements are performed with a beam of sodium atoms in a uniform electric field of \ensuremath{\sim}3.2 kV/cm excited via the 3 $^{2}P$ state to \ensuremath{\sim}285 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (${n}^{\mathrm{*}}$\ensuremath{\sim}20) below the zero-field ionization threshold, and hence substantially above the classical saddle-point energy. For mixed states at level crossings, the discrete-continuum couplings interfere, yielding resonances that are stabilized against ionization over a small interval of the field. Measurements of the maximum lifetimes of \ensuremath{\Vert}m\ensuremath{\Vert}=1 levels here are not limited by laser bandwidth, as were our previous spectral observations of m=0 resonances. For three narrowing regions studied here, the observed maximum lifetime values of 127\char21{}191 nsec are 10\char21{}20 % less than values obtained from WKB-QD calculations, while experimental error limits are \ensuremath{\sim}5%. After considering estimates for competing processes, namely radiative decay and transfer by blackbody radiation, a slight discrepancy remains.

Pure rotational transitions of allene in excited vibrational states observed by microwave Fourier transform spectroscopy using Stark and double resonance techniques

Pure rotational transitions of allene in the degenerate vibrational states v9=1, v10=1, and v11=1 have been observed with a pulsed microwave Fourier transform spectrometer. The assignment of the J=0→1 transitions was confirmed by microwave–microwave double resonance experiments. From the latter and from Stark effect measurements the magnitude of the vibrationally induced dipole moments have been determined. The rotational constants known from high-resolution infrared spectra have been improved.

Nuclear quadrupole structure of potassium hydroxide in the 32 GHz microwave region

A high temperature Stark and radiofrequency-microwave double resonance spectrometer was used to observe the nuclear quadrupole structure of the J=2←1 transition of 39KOH in a number of vibrational states. First order analysis of the hyperfine components gave nuclear quadrupole coupling constants of eQq=−7.23 (29) MHz for the (0000) state, eQq=−7.16 (33) MHz for the (1000) state, and eQq=−7.29 (37) MHz for the (0110) state.

Electronic structure and transport properties of GaAs-GaAlAs superlattices in high perpendicular electric fields

We present a study of the effect of high (∼1×105 V/cm) perpendicular electric fields on the electronic structure of a GaAs-Ga0.7Al0.3As superlattice represented by five quantum wells separated by 70-Å barriers. An exact solution is obtained by using the transfer-matrix technique to match the Airy functions at the interfaces. The method of phase-shift analysis is employed to evaluate the energy levels, the width of the Stark resonances, the real-space wave functions, and the time of flight associated with the field-induced phenomena. Wells of 50- and 70-Å width are used to elucidate the relationship between level depth and field. The quantum states above the semiclassical confining barrier, which have so far been represented by a continuum, are correctly accounted for. These states are mainly localized in the barrier material. It is shown that the real-space localization and bandwidth of these states are significantly altered by the external field. In particular, we evaluate the time delay for electrons above the barrier due to the field-induced change in the density of states, which is related to the presence of the above higher-lying confined states and which would be observed in current–voltage measurements.

Exact calculations of quasibound states of an isolated quantum well with uniform electric field: Quantum-well Stark resonance.

Exact calculations of quasibound states of an isolated quantum well with uniform electric field: Quantum-well Stark resonance.

Stark-cell stabilization of a CH_2F_2 laser pumping source

We have used the Stark-cell stabilization technique to control and tune a CO2 laser employed to pump a CH2F2 submillimeter wave laser at 214 μm. The selected Stark resonances are the 423 ← 524, ΔM = −1 transitions of the ν9 vibrational band of CH2F2. With a cell length of 255 mm, an electrode spacing of 389.6 μm, and a gas pressure of 250 mTorr, we achieve on the 9R34 CO2 line a frequency stability of ±1 MHz over a usable 60-MHz tuning range. On the M = 1 → 2 transition, we observe a tuning rate of 2.7 MHz mm/V in good agreement with the calculated value from known spectroscopic constants. The technique is fairly general and can be applied with the same Stark gas to several other CO2 pumping lines.

Microwave spectral study of 3-fluorobenzonitrile

The microwave spectrum of 3-fluorobenzonitrile has been observed and analyzed in the KU (12.5–18.0 GHz) and the K (22.0–26.0 GHz) bands. Both Stark and radio frequency-microwave double resonance spectroscopy have been used in the observation and assignments. Analysis of the spectrum yields three rotational constants (all in MHz), A = 3388.59 ± 0.02, B = 1186.64 ± 0.01, C = 878.72 ± 0.01, and five quartic centrifugal distortion terms (all in MHz), d J = (1.7 ± 0.6) × 10 −4 , d JK = (−4.9 ± 1.1) × 10 −3 , d K = (−10.5 ± 2.4) × 10 −3 , d WJ = (−1.0 ± 1.0) × 10 −7 , d WK = (4.8 ± 1.1) × 10 −6 , for the molecule. An r 0 structure has been proposed which does not suggest serious distortion of the benzene ring. The inertia defect of the molecule is 0.1 amu A ̊ 2 .

Laser stark spectroscopy of the ν2 fundamental band of 15NH 3

The ν 2 fundamental band of 15NH 3 has been observed with a laser Stark spectrometer in Doppler-limited resolution. A set of 38 band constants including the electric dipole moment and its rotational dependence are determined from 416 Stark resonances observed in the present work and three submillimeter lines reported in the literature. The ν 2-band absorption line frequencies in the region 800–1160 cm −1 and their relative absorption intensities are estimated from the band constants.

Laser Stark spectroscopy; a case study in the ν2 fundamental band of 14NH 3

The ν 2 fundamental band of 14NH 3 is observed with a laser Stark spectrometer in Doppler-limited resolution. A set of 41 constants including the electric dipole moment and its rotational dependence are determined from 360 Stark resonances observed in the present work and 67 millimeter- and submillimeter-wave inversion and rotation-inversion lines reported in the literature. The rms residual of the fit is 3.1 × 10 −4 cm −1. Field-free transition frequencies of the band in the region 800–1160 cm −1 are calculated from the constants and tabulated together with their estimated uncertainties and relative absorption intensities. Rotational dependence of the electric dipole matrix elements of a C 3 v molecule is presented on the basis of the conventional theory of vibration-rotation.

The high resolution infrared spectrum and laser Stark spectroscopy of thev 8 band of propyne

The perpendicularv8 band lying in the 1000–1100 cm−1 region has been studied from infrared and laser Stark, spectra. We were interested in the part of spectrum corresponding to the spectral range of the 9 μm CO2 laser lines. Assignments of rovibrational lines with J'<40 and K'<6 have been made. About 100 Stark resonances have been assigned to 12 rovibrational transitions. Effective molecular constants and dipole moment have been determined with high accuracy. A list of close resonances with CO2 laser lines is given and may be used for optical pumping experiments.

Combined subdoppler laser-Stark and millimeter-wave spectroscopies: Analysis of the ν6 band of CH 335Cl

The ν 6 fundamental of CH 3 35Cl has been remeasured by using a Stark-Lamb-dip technique. These Stark resonances were combined with the zero-field microwave spectra to give determinable combinations of the vibration-rotation parameters and the dipole moments: μ″ = 1.89628(23)D and μ′ = 1.89738(19)D.

Electric field induced shifts and lifetimes in GaAs-GaAlAs quantum wells

We have performed an exact numerical calculation for an isolated GaAs quantum well system subjected to an external electric field. This calculation predicts both the shifts and widths of the Stark resonances. The shift predictions are in agreement with recent experimental results and the width calculations allow the observed decrease in luminescence lifetime with field to be interpreted in terms of the field-induced tunneling of the carriers.

Laser Stark spectroscopy of the coriolis coupled ν2 and ν5 bands of CD 3Cl

About 940 Stark resonances for CD 3 35Cl and 610 resonances for CD 3 37Cl have been measured by using a CO 2 laser with the 9- and 10-μm regions. They were assigned to 59 rovibrational transitions of ν 2 ( J′ ≤ 37, K ≤ 14) and 200 of ν 5 ( J′ ≤ 47, −14 ≤ k′ l′ ≤ +10) for 35Cl, and 31 of ν 2 ( J′ ≤ 12, K ≤ 10) and 175 of ν 5 ( J′ ≤ 46, −14 ≤ k′ l′ ≤ +9) for 37Cl. These data, combined with the microwave and FIR data in the ν 2 and ν 5 states, were analyzed by taking account of the Coriolis interaction between ν 2 and ν 5, and the (2, 2) and (2, −1) interactions in ν 5. Several Δ K = +2 transitions of the ν 5 band were observed in the Stark spectra, and the ground state constants, A 0 and D K0 , were determined precisely for both 35Cl and 37Cl species. Also, the vibrationally induced dipole moments were obtained. The molecular constants and the zero-field transition frequencies of the ν 2 and ν 5 bands were determined.

Interference narrowing at crossings of sodium Stark resonances.

We have observed a striking line narrowing in the photoionization spectrum of sodium atoms in an electric field. At crossings of two relatively broad resonances, one of them is narrowed by 2 to 3 orders of magnitude as a result of interference between the discrete and continuum coupling amplitudes that mediate their ionization. The observations agree quantitatively with WKB quantum-defect Stark theory and also with a simpler model involving two discrete states and two continua.

CO2 and CO laser microwave double resonance spectroscopy of OCS: Precise measurement of dipole moment and polarizability anisotropy

Laser–microwave double resonance (LMDR) with high electric field was applied to the OCS molecule. Stark Lamb-dip spectra due to the infrared transitions of the 2ν2(0200–0000, 9.6 μm), 2ν1 (2000–0000, 5.8 μm), and ν1+2ν2 (1200–0000, 5.3 μm) bands were observed with the CO2 and CO lasers. The spectra due to the corresponding hot bands; 0310–0110, 0400–0200, 1200–1000, 1310–1110; 2110–0110, 3000–1000; 1400–0200, 1420–0220, 1510–0310, 2200–1000; and a few bands of OC34S and O13CS were also identified. Associated with these infrared transitions, more than 90 LMDR signals were detected and assigned to rotational transitions in the 11 vibrational states 0000, 1000, 2000, 0110, 0200, 0220, 0310, 0400, 1200, 1420, and 2200 of the normal species, and in the two vibrational states 0000 and 0200 of both OC34S and O13CS. Dipole moments were determined with accuracies (2.5σ) better than 2×10−5 D for all these vibrational states. Polarizability anisotropies were also obtained for some states. The data for the ground ν1 and ν2 vibrational states are, with the 2.5σ uncertainties in parentheses.From the Stark Lamb-dip spectra the origins of various vibrational bands were determined, among which those for the 0200–0000 and 0310–0110 bands are 31 389 530.4(25) and 31 566 477.57(67) MHz, respectively. The dipole moments and band origins obtained in the present study agree well with the available accurate values from molecular beam electric resonance and heterodyne measurement, respectively. A procedure for the calibration of electric field in laser Stark and double resonance spectroscopy, in which the dipole moment of OCS is used as the standard, is described.