Double Resonance Transitions Research Articles

Microwave measurements, calculations, and analysis for the gas phase ammonia-formic acid dimer

The gas-phase doubly hydrogen-bonded formic acid-ammonia complex was obtained by heating a sample of ammonium formate in neon. High-level DFT and MP2 calculations with various basis sets were performed and barriers for proton tunneling and internal rotation were determined. The microwave spectrum was measured in the 7–16 GHz frequency range using a Flygare-Balle type pulsed beam Fourier transform microwave (FTMW) spectrometer. Double resonance transitions were observed near 20 GHz. Rotational transitions were measured and fitted for two vibrational states to obtain the rotational constants and quadrupole coupling constants. The rotational constants were determined to have the following values: A = 12017.0(2), B = 4337.331(2), and C = 3227.279(2) for the 0+ state and A = 12017.0, B = 4302.02(1), and C = 3238.161(1) for the 0− state and have been fit to 16 transitions and 9 transitions respectively. Each state was fit to a rigid model showing quadrupole splitting and compared with computations.

Comb-locked cavity-assisted double-resonance molecular spectroscopy based on diode lasers.

Interactions between a molecule and two or more laser fields are of great interest in various studies, but weak and highly overlapping transitions hinder precision measurements. We present the method of comb-locked cavity-assisted double resonance spectroscopy based on narrow-linewidth continuous-wave lasers, which allows for state-selective pumping and probing of molecules. By locking two near-infrared diode lasers to one cavity with a finesse at the order of 105, we measured all three types of double resonances. Carbon monoxide molecules with selected speeds along the laser beam were excited to vibrationally excited states, and absorption spectra with sub-MHz linewidths were observed. Positions of double resonance transitions were determined with an accuracy of 3.7 kHz, which was verified by comparing to Lamb-dip measurements. The present work paves the way to the pump-probe study of highly excited molecules with unprecedented precision.

Sub-Doppler Double-Resonance Spectroscopy of Methane Using a Frequency Comb Probe.

We report the first measurement of sub-Doppler molecular response using a frequency comb by employing the comb as a probe in optical-optical double-resonance spectroscopy. We use a 3.3 μm continuous wave pump and a 1.67 μm comb probe to detect sub-Doppler transitions to the 2ν_{3} and 3ν_{3} bands of methane with ∼1.7 MHz center frequency accuracy. These measurements provide the first verification of the accuracy of theoretical predictions from highly vibrationally excited states, needed to model the high-temperature spectra of exoplanets. Transition frequencies to the 3ν_{3} band show good agreement with the TheoReTS line list.

Measurement and assignment of double-resonance transitions to the 8900–9100- cm−1 levels of methane

Optical-optical double-resonance spectroscopy with a continuous wave pump and frequency comb probe allows measurement of sub-Doppler transitions to highly excited molecular states over a wide spectral range with high frequency accuracy. We report on assessment and characterization of sub-Doppler double-resonance transitions in methane measured using a 3.3-$\ensuremath{\mu}\mathrm{m}$ continuous wave optical parametric oscillator as a pump and a 1.67-$\ensuremath{\mu}\mathrm{m}$ frequency comb as a probe. The comb spectra were recorded using a Fourier transform spectrometer with comb-mode-limited resolution. With the pump tuned to nine different transitions in the ${\ensuremath{\nu}}_{3}$ fundamental band, we detected 36 ladder-type transitions to the $3{\ensuremath{\nu}}_{3}$ overtone band region, and 18 V-type transitions to the $2{\ensuremath{\nu}}_{3}$ overtone band. We describe in detail the experimental approach and the pump stabilization scheme, which currently limits the frequency accuracy of the measurement. We present the data analysis procedure used to extract the frequencies and intensities of the probe transitions for parallel and perpendicular relative pump-probe polarization. We compare the center frequencies and relative intensities of the ladder-type transitions to theoretical predictions from the TheoReTS and ExoMol line lists, demonstrating good agreement with TheoReTS.

Mass-independent Dunham analysis of the known electronic states of platinum sulfide, PtS, and analysis of the electronic field-shift effect.

Several new vibrational bands of the [12.5] Ω = 0+-X3Σ- Ω=0+ and the [15.9] B Ω = 0+-X3Σ- Ω=0+ transitions have been observed in high resolution absorption measurements recorded using Intracavity Laser Spectroscopy (ILS). These new bands have been rotationally analyzed and incorporated into a comprehensive PtS dataset that was fit to a mass-independent Dunham expression using PGOPHER. The comprehensive dataset included all reported field-free, gas phase spectroscopic data for PtS, including 32 Fourier transform microwave transitions (estimated accuracy: 1 kHz), 9 microwave/optical double resonance transitions (25 kHz), 51 millimeter and submillimeter transitions (25-50 kHz), 469 molecular beam-laser induced fluorescence transitions (0.003 cm-1), and 4870 ILS transitions (0.005 cm-1). The determined equilibrium constants have been used with the Rydberg-Klein-Rees method to produce potential energy curves for the four known electronic states of PtS. Isotopic shifts in electronic transition energy beyond expectations from the Born-Oppenheimer approximation were observed and treated as electronic field-shift effects due to the difference in the nuclear charge radius between Pt isotopes. The magnitude and sign of the determined field-shift parameters are rationalized through the analysis of the previously reported ab initio calculations.

Polarization spectroscopy to determine alignment depolarization of the [formula omitted] atoms using a pump-probe laser technique

We have experimentally investigated alignment depolarization cross section of the excited J = 3 / 2 133Cs atoms, by collisions with ground level krypton atoms, from a two-photon two-color linear polarization spectra. To measure the linear polarization degree of the 6 s 2 S 1 / 2 → 6 p 2 P 3 / 2 → 10 s 2 S 1 / 2 double-resonance transition, a nanosecond pulse pump-probe laser technique was employed. Alignment was optically induced by linear polarization of the pump laser. By analyzing the intensity of the cascade fluorescence signal, monitored from the 9 p 2 P 1 / 2 → 6 s 2 S 1 / 2 transition at 361.73 nm, in the presence of Kr pressures ranging from 7 mbar to 133 mbar a depolarization cross section value of 294 ( 45 ) Å 2 is obtained.

Measurement of absolute transition dipole moment functions of the 3 Π1→1(X)Σ1+ and 3 Π1→2(A)Σ1+ transitions in NaK using Autler–Townes spectroscopy and calibrated fluorescence

We describe a two-laser experiment using optical-optical double resonance fluorescence and Autler-Townes (AT) splittings to determine the NaK 3 (1)Pi-->1(X)(1)Sigma(+), 2(A)(1)Sigma(+) absolute transition dipole moment functions. Resolved 3 (1)Pi-->A (1)Sigma(+) and 3 (1)Pi-->X (1)Sigma(+) fluorescence was recorded with the frequencies of a titanium-sapphire laser (L1) and a ring dye laser (L2) fixed to excite particular 3 (1)Pi(upsilon = 19,J = 11,f)<--A (1)Sigma(+)(upsilon('),J(') = J = 11,e)<--X (1)Sigma(+)(upsilon("),J(") = J(')+/-1,e) double resonance transitions. The coefficients of a trial transition dipole moment function mu(e)(R) = a(0)+a(1)(R(eq)/R)(2)+a(2)(R(eq)/R)(4)+... were adjusted to match the relative intensities of resolved spectral lines terminating on the lower A (1)Sigma(+)(upsilon('),11,e) and X (1)Sigma(+)(upsilon("),11,e) levels. These data provide a relative measure of the functions mu(e)(R) over a broad range of R. Next, L2 was tuned to either the 3 (1)Pi(19,11,f)<--A (1)Sigma(+)(10,11,e) or 3 (1)Pi(19,11,f)<--A (1)Sigma(+)(9,11,e) transition and focused to an intensity large enough to split the levels via the AT effect. L1 was scanned over the A (1)Sigma(+)(10,11,e)<--X (1)Sigma(+)(1,10,e) or A (1)Sigma(+)(9,11,e)<--X (1)Sigma(+)(0,12,e) transition to probe the AT line shape, which was fit using density matrix equations to yield an absolute value for mu(ik) = integral psi(vib) (i)(R)mu(e)(R)psi(vib)(k)(R)dR, where i and k represent the upper and lower levels, respectively, of the coupling laser (L2) transition. Finally, the values of mu(ik) were used to place the relative mu(e)(R) functions obtained with resolved fluorescence onto an absolute scale. We compare our experimental transition dipole moment functions to the theoretical work of Magnier et al. [J. Mol. Spectrosc. 200, 96 (2000)].

Optical–optical double resonance spectroscopy of the [formula omitted] transition of CaOH

The D ˜ 2 Σ + state of CaOH was investigated using optical–optical double resonance spectroscopy. A combined least-squares fit of the D ˜ 2 Σ + – A ˜ 2 Π double resonance transition data along with A ˜ 2 Π – X ˜ 2 Σ + optical transition data and the millimeter-wave pure rotational data of the X ˜ 2 Σ + state was performed using an effective Hamiltonian. The spin–rotation constant was determined for the D ˜ 2 Σ + state for the first time. An analysis of these constants showed that the Ca–O bond length and spin–rotation parameter of the D ˜ 2 Σ + state have the smallest values of all the observed 2Σ + states of CaOH. This evidence suggests the assignment of the D ˜ 2 Σ + state as arising from a Ca + atomic orbital of mainly 5 sσ character. This atomic orbital assignment was shown to be consistent with both previous work on CaF and recent theoretical calculations on CaOH.

Rare gas–iodine complexes in the ion-pair states

Abstract Luminescence and luminescence excitation spectra in the vicinity of the optical–optical double resonance transitions to the I 2 ( f 0 g + , v f = 8 and 9, J f ≈ 55) levels have been measured at the bulb conditions for the I 2 + Rg mixtures (Rg = He, Ar, Xe) at the rare gas pressures 2–20 Torr and room temperature. Luminescence attributed to the RgI 2 complexes in the f 0 g + , F 0 u + and E 0 g + ion-pair states has been observed for the first time. It is argued that the complexes can be formed by direct optical excitation from the RgI 2 ( B 0 u + ) complexes or { Rg + I 2 ( B 0 u + ) } colliding pairs. Besides, the RgI 2 complexes in the f 0 g + , F 0 u + and E 0 g + ion-pair states can be formed in nonadiabatic internal conversion processes from the RgI 2 ( f 0 g + ) one. The complexes have rather long lifetime, especially in the case of Xe, and decay radiatively and nonradiatively forming I 2 molecules in different ion-pair states.

Absolute Position of the D′2g(3P2) Ion-Pair State of I2 Determined by Perturbation-Facilitated Optical–Optical Double Resonance

We have reexamined the sequential two-photon absorption of I2 from the X1Σg+ ground state to the lowest D′2g(3P2) ion-pair state using the high vibrational level of the B3Π(0u+) state as an intermediate. The double resonance transition to the D′2g(3P2) state was found to occur through the B3Π(0u+)–b′2u coupled state by hyperfine interaction, which permits to mix the different J levels of different electronic states. We elucidated the B3Π(0u+)–b′2u coupling schemes in the intermediate states. The double resonance spectra recorded for the D′2g(3P2) state in the range v=0–30 were used to determine the absolute energy of the D′2g(3P2) state. The molecular parameters of the D′2g(3P2) state obtained in this study are Y00=40 388.783(2), Y10=103.956 46(57), Y20=−0.207 717(51), Y30=2.199(13)×10−4, Y01=0.020 528 18(62), and Y11=−5.1753(48)×10−5 (all in cm−1 and σ in parentheses). An RKR potential curve constructed using these constants is reported. Combined with the data on the D′2g(3P2)–A′3Π(2u) transition from Zheng et al. (J. Chem. Phys.96, 4877 (1992)), we can locate the A′3Π(2u) v=0 state at 10 096.444(6) cm−1 above the ground state.

Line shapes of cascade two-photon transitions in a cesium magneto-optic trap

We present a study of a two-photon double-resonance transition in cold cesium atoms in a magneto-optic trap. A closed five-level density matrix model of the system is developed to characterize the double-resonance Autler–Townes-split absorption line shape. Comparing this model with experimental spectra, we gain insight into the dominant process involved in trapping atoms, in particular, the importance of the interference of the six trapping laser beams. This system is used to probe transient effects in the trap as well as collective effects of the trapped atom cloud resulting from the intentional misalignment of the trapping beams.

Excited-state Structure and Dynamics of Nitric Oxide probed by Resonant Four-wave Mixing Techniques

We review the results from two experiments that used resonant four-wave mixing (RFWM) techniques to investigate double-resonance transitions in NO. In the first experiment, laserinduced grating decay curves that reveal quantum beats due to the hyperfine structure of the A 2Σ, υ' = 0 state were observed and interpreted. In the second, multistate interactions between the L 2II1/ 2,3/2, υ = 8 and Q 2II1/ 2,3/2, υ = 0 states were investigated, and new assignments were made. The results highlight the potential of RFWM techniques for probing excited-state physics.

Strain broadening of optical transitions with hyperfine structure

In this paper we report the different hyperfine structures of the 594-nm optical transition in several ${\mathrm{CaF}}_{2}$:${\mathrm{Pr}}^{3+}$:${\mathrm{Sr}}^{2+}$ crystals as well as the associated optical-microwave double-resonance behavior. Using the observed signals with different ${\mathrm{Sr}}^{2+}$ dopant concentrations, the consequences of strain on the optical line shape and the optical-microwave double-resonance transitions is discussed.

Double resonance spectroscopy of laser-cooled Rb atoms

Double resonance transitions have been observed in laser-cooled and trapped 85Rb atoms. The atoms are cooled on the 5S 1 2 - 5P 3 2 transition and the absorption of a weak probe beam tuned to the 5P 3 2 -4D 5 2 transition is detected. The suitability of this transition as a potential secondary frequency standard in the near infra-red is assessed by using the Autler-Townes splitting as a sensitive probe for the shifts induced by the pump laser. The dependence of the splitting on the pump detuning and intensity are measured. Systematic shifts of a few hundred kHz seem realistic, subject to an accurate knowledge of the detuning of the cooling laser. New precise values are also obtained for the hyperfine constants for the 4D 5 2 level: A = -5.06 ± 0.10 MHz and B = 7.42 ± 0.15 MHz.

Double-resonance laser-induced grating spectroscopy of nitric oxide

Double-resonance laser-induced grating spectroscopy (LIGS), including two-color laser-induced grating spectroscopy (TC-LIGS) and degenerate four-wave mixing (DFWM) spectroscopy, has been used to probe the E 2Σ, ν=0←A 2Σ, ν′=0←X 2Π 1 2 , ν″=0 double-resonance transitions in NO. Several different double-resonance schemes have been implemented and their relative merits are discussed. The results demonstrate that double-resonance LIGS shows considerable promise for obtaining state-selective absorption spectra of rovibronically excited states for a wide variety of molecules.

Experimental distinction of electric and magnetic transition moments

The rotational band structure of a magnetic dipole vibronic transition is exactly the same as that of an electric dipole vibronic transition. It is often assumed that molecular vibronic transitions are electric dipole, introducing an ambiguity about the change in symmetry if the transition is weak enough to be an allowed magnetic dipole transition and the symmetry of either vibronic state is unknown. In atomic spectroscopy, it is known that either the Zeeman effect or the polarization dependence of wide angle fluorescence interference can be used to distinguish among electric-dipole, magnetic-dipole, electric-quadrupole, enforced-dipole transitions, etc. This note points out that rotationally resolved double resonance using polarized light can be used to determine the type of an unknown multipole transition if the type (magnetic or electric) of the other double resonance transition is known. Stark and Zeeman effects are valuable special cases since the type of the Stark (or Zeeman) transition moment is known a priori to be electric (or magnetic) dipole. Published Stark spectra of formaldehyde-d2 experimentally prove Innes’ assignment of a magnetic dipole transition.

Sputtering of LiF(100) with low energetic Ne+ and Ne2+ ions

Sputtering of a LiF(100) surface by singly and doubly charged Ne ions with impact energies between 10 and 500 eV has been performed. The emission of Li+, Li0, F+ F0 and LiF+ was measured by means of a quadrupole mass spectrometer. The yield of sputtered Li+ ions and Li0 atoms decreases with decreasing impact energy and is slightly higher for Ne2+ compared to Ne+ at impact energies below 100 eV. The situation changes very drastically regarding the emitted F particles. In the whole energy range investigated, the F+ and F0 yield was about one order of magnitude larger if Ne2+ projectiles were used instead of Ne+. According to the experimental data we propose the following model for the emission of F+ [1,2]: (1) The F ion of the solid surface is changed to F+ by Auger neutralization of the Ne2+ into Ne+ or by double resonance transition into doubly excited states of Ne0 with subsequent autoionization into Ne+. These processes take place several Ångströms in front of the surface. (2) The initial repulsive forces between the F+ ion and the surface are changed into attractive ones within a very short time by rearrangement of the alkali halide lattice [2]. (3) The neutralized projectile sputters the F+ as in a normal sputtering event on a surface with low surface binding energy, and F+ can he emitted as long as the kinetic energy of the projectile is sufficiently high.

Infrared-radiofrequency double-resonance spectroscopy of CD 3Br

An infrared microwave sideband laser source operating in the 10 μm region has been used with the method of infrared-radiofrequency double resonance to record radiofrequency spectra in the ground and ν 2=1 vibrational states of CD 3Br. The frequencies to ∼200 and ∼160 pure quadrupole transitions have been observed for CD 3 79Br and CD 3 81Br, respectively, approximately half in the ground state and half in the ν 2=1 vibrational state of each species. The frequencies have been used to determine the quadrupole coupling constants, including centrifugal distortion parameters, and spin-rotation constants for the bromine nucleus in each species. A double-resonance effect that causes an apparent shift in frequency for each of a pair of closely-spaced double-resonance transitions has been discovered experimentally and explained theoretically.

Optical–optical double resonance spectroscopy of Br2 through the A 3Π(1u) state: Analyses of the 1u and 0−u(3P1) ion-pair states

The technique of optical–optical double resonance is applied to study the ion-pair states of Br2 correlating to Br−(1S)+Br+(3P1). The Br2 molecules in the ground state are pumped to the A3Π(1u) state as an intermediate, and subsequently excited into the ion-pair states by a coherent two-photon transition. The double resonance transition is detected through the dispersed fluorescence terminating on the lower valence states. The 1u(3P1) ion-pair state is observed for the first time and the energy level analyses are made on the v=0 to v=10 levels in detail. The 0−u (3P1) state is also identified through the heterogeneous interaction with the 1u(3P1) state, which is interpreted in terms of the pure precession approximation. The molecular parameters thus obtained in the Dunham expansion are Y00=53 257.605(10), Y10=164.1571(69), Y20=−0.7588(15), Y30=5.650(98)×10−3, Y01=0.040 011 6(40), Y11=−1.7488(42)×10−4, and Y02=−8.40(53)×10−9 for the 1u(3P1) state of 79Br2 isotope species (all in cm−1 with 3σ in parentheses). The main parameters of the 0−u(3P1) state are Y00=53 479.72(25), Y10=148.620(54), and Y01=0.038 021 5(79).

Optical-optical double-resonance spectroscopy of the 1 g( 3P 1) ion-pair state of Br 2

The 1 g ( 3P 1) ion-pair state of Br 2 has been observed for the first time by optical-optical double-resonance spectroscopy. The ion-pair state was excited from the X 1Σ g + ground state stepwisely through the A 3Π(1 u ) state: 1 g( 3 P 1)-A 3 Π(1 u)-X 1 Σ g + . The double-resonance transitions were then detected by the 265-nm emission which originated from the 1 g ( 3P 1) state radiating back to the A 3Π(1 u ) state. Energy level analysis of the 1 g ( 3P 1) state was made on the v = 0 to v = 9 levels of the 79Br 2 isotope species, giving the molecular parameters T e = 52 641.554(20), ω e = 153.8654(71), ω e χ e = 0.42863(69), B e = 0.042496(11), α e = 1.7005(84) × 10 −4, D e = 1.22(16) × 10 −8, and q = 1.13(23) × 10 −5 (all in cm −1 with 3σ in parentheses).