Infrared-microwave double resonance of propynal by using the 3.51 μm HeXe laser

The 3.51 μm HeXe laser is magnetically tuned over a wavenumber of 0.2 cm^?1 and used for infrared absorption and double resonance spectroscopy. Eight rotation-vibration lines of propynal in the ν₂ band are assigned by the Stark effect. Eleven microwave transitions in the v₂ = 1 vibrational state are observed by the method of infrared-microwave double resonance. The rotational constants of the excited state and the band origin of the vibration ν₂ are determined from the observed spectra.     

Infrared-microwave double resonance in CH3OH using a Zeeman-tuned 3.5-μm HeXe laser

Infrared microwave double resonance signals have been observed for CH₃OH using the 3.5-μm HeXe laser line. When microwave transitions in the ground vibrational state are pumped, the double resonance signals are obtained on two infrared transitions v = 1 ← 0 of ν^CH(a′); v = 1, J, K, μ = 4, 2, 1 ← v = 0, J, K, μ = 3, 2, 1, and 4, 3, 1 ← 3, 3, 1. Three weak double resonance signals are due to the collision-induced transitions. Their relative intensities have been explained successfully by using the rate constants of collision-induced transitions which are proportional to the dipole matrix elements between the states involved in the transitions.     

Infrared-microwave double resonance in CF3I; Microwave spectroscopy in emission and absorption

From the double resonance effects observed on the microwave spectrum of CF₃I it has been shown that the R(16) CO₂ laser line of the 9.4 μm band is coincident with the R(7), K = 2, $\text{F =}\text{19}\text{2}\text{→}\text{21}\text{2}$ transition of the CF₃, symmetric stretch (ν₁ band) of CF₃I. Using this laser line, 50 double resonance signals all with K = 2 were observed ranging from J = 4 → 5 to J = 12 → 13 transition. The fact that double resonance effects were observable over such a large range of J was explained as being caused by very strong ΔJ = ± 1, ΔK = 0 collisional transitions.Extremely large pumping effects were produced using 6 W of laser radiation, which caused relative changes in intensity ($\text{Δ}\text{I}\text{I}$) in ground state lines of up to 25. The population transfer into the excited state was so large that many excited state lines, which had previously been undetectable, produced signals up to 30 times more intense than the corresponding undisturbed ground state lines (i.e., values of $\text{Δ}\text{I}\text{I}$ of ～6000 were achieved). Population inversions were produced by the laser pump in many of the K = 2 microwave transitions, not only in those with levels directly pumped by the laser but also in some connected only by collisional transitions. The results was that many of the signals were observed as stimulated emissions rather than absorptions.The rotational constant and quadrupole coupling constants of CF₃I in the v₁ excited state are calculated and an estimation of the center of the ν₁ band is made. The absolute population shifts produced by the laser pump are estimated and the rate constants of the collisional transitions are discussed.     

Spin-selective electron tunneling from excited FA centers to F+ centers in CaO

From pulsed phosphorescence microwave double resonance experiments it is established that electron tunneling between F_A and F⁺ centers in CaO occurs from F_A centers in the excited ³A₁ state. Only the radiative sub-levels within this ³A₁ state act as precursor states in the electron transfer process. The tunneling rate at 1.2 K is determined to be 1.5±0.2s^-1.     

Infrared-microwave double resonance of 12CH3OH with a CO2 laser

The Stark effect of the 2₂ ← 2₁(E₁), 2₁ ← 3₀(E₁) microwave transitions in the ground state and the 2₂ ← 2₁(E₁) microwave transition in the first excited CO stretching vibrational state are measured by means of infrared-microwave double resonance with the ^qQ₁(2)E₁ infrared transition as the pump transition in the range of 1000 to 2300 V/cm. The dipole moments μ_a and μ_b as well as the off-diagonal rotational constant D_ab are determined for both the ground and the excited states. The frequency of the ^qQ₁(2)E₁ infrared transition is found to be lower by 128 ± 2 MHz than that of the P(34) CO₂ laser.     

Two-photon spectroscopy of 15NH3 with isotopic CO2 lasers and double resonance studies with a new coincidence

Eleven transitions of the ν₂ band of ¹⁵NH₃ were measured by the technique of infrared-microwave two-photon spectroscopy using an isotopic CO₂ laser and 20-mW microwave power. By combining these results with those of previous two-photon measurements and with Stark laser spectroscopy results, the spectroscopic constants of this band were calculated. Using the previously unknown coincidence between the R(18) ¹³CO₂ laser line and the _asQ(5,4) infrared transition, velocity tuned multiple-photon Lamb-dip signals were observed. Very intense double resonance signals were observed on the (5,4), (6,4), and (4,4) microwave transitions and the magnitude of these effects was compared to those observed previously in ¹⁴NH₃.     

Nuclear reactions as an example of the quantum theory of irreversible processes

A modification of the atomic beam magnetic resonance method for investigation of the hyperfine structure of excited atomic states will be described. Radiofrequency transitions between the hyperfine structure niveaus of the excited state, which are unequally populated by circularly polarized light, are detected by observing the resulting change in population number of the hyperfine structure niveaus of the ground state using magnetic deflection in an inhomogeneous field and additional radiofrequency transitions in the ground state as analyzers. As an application the hyperfine structure of the excited 4² P _3/2-state of K³⁹ has been investigated in an almost strong magnetic field of about 65 G with a constant frequency of the applied radiofrequency field of 125.50 Mc/s. The analysis of the radiofrequency signal of the excited state detected as a change in the amplitude of a radiofrequency transition in the ground state yielded the valuesA=(6.10±0.25) Mc/s andB=(1.8±1.2) Mc/s for the hyperfine structure constants of the 4² P _3/2-state of K³⁹. Further possibilities for observing signals of the excited state with the apparatus used in this experiment are also discussed.     

Microwave spectrum of torsionally excited acetic acid

The microwave spectrum corresponding to the first excited state of the methyl torsion in acetic acid has been identified by means of microwave-microwave double resonance. Although the A-E splittings are extremely large, a reasonable fit has been obtained for the v = 0 and v = 1 states simultaneously by using a Hamiltonian which allows for geometry relaxation upon internal rotation. Barrier parameters are V₃ = 169.90 ± 0.06 cm^?1 and V₆ = ?6.74 ± 0.02 cm^?1. An interpretation of the parameters describing nonrigidity is given in terms of a model with two relaxing bond angles, which is qualitatively supported by ab initio calculations.     

A superior microwave absorption material: Ni2+-Zr4+ Co-Doped barium ferrite ceramics with large reflection loss and broad bandwidth

Large reflection loss and wide bandwidth are significant targets, determining the microwave absorption ability. However, it is still a challenge to simultaneously satisfy the two conditions. As a multifunctional material, BaFe₁₂O₁₉ possess excellent electromagnetic properties in the microwave frequency band. Due to the natural resonance phenomenon of the material, BaFe₁₂O₁₉ can produce a large magnetic loss which correlates with Fe³⁺ content, and the microwave absorption characteristics of barium ferrite can be modulated by ion doping. As a typical magnetic metal, Ni coupled with high-valence state Zr⁴⁺ doping helps to produce double resonance peaks. In this work, Ni²⁺-Zr⁴⁺ co-doping M-type barium ferrites (BaFe_12-2xNi_xZr_xO₁₉, BNZFO-x, x = 0–0.8) were prepared conveniently by solid-state reaction method. Several necessary measurements to characterize its microwave absorption property have been operated such as morphology, magnetic performance and electromagnetic parameters. The results show that reflection loss and bandwidth can be simply tuned by tailoring Ni²⁺-Zr⁴⁺ content. The reflection loss peak drifts from 18 GHz to 9.76 GHz, which involves a half of the studied frequency range. The maximum reflection loss achieves −60.6 dB and the corresponding bandwidth over −10 dB is 7.68 GHz for BNZFO-0.6 ceramic with only 2.1 mm thickness. Thus, the doping of Ni²⁺-Zr⁴⁺ ion pairs is beneficial to improve the absorbing properties of the material, and the superior microwave absorption property may originate from its inner double natural resonance in micro-scale. The excellent microwave absorption properties suggest that BNZFO-x is a promising candidate applied for designing electromagnetic shielding devices.     

The a-type rotational spectrum of HNCS in the excited bending states

The microwave and millimeter wave spectra of HNCS in the three bending excited states, v₄ = 1, v₅ = 1, and v₆ = 1, have been measured. The ^qR₀, ^qR₁, and ^qR₂ branches for each of these three states and the ^qR₃ branch for the lowest excited state have been assigned. Effective rotational and centrifugal distortion constants have been determined for each vibrational and K_a-rotational sub-state. Two local resonances, caused by the Coriolis induced asymmetry interaction and a b-type Coriolis resonance, allow unambiguous confirmation of the assignment of the state v₆ = 1, the first excited state of the out-of-plane vibration.     

EPR and NMR characterization of theS=9 excited state and spin density distribution in the single-molecule magnet Fe8Br8: Implications to theS=10 model and magnetization tunneling pathways

High-sensitivity, variable-frequency, high-field electron paramagnetic resonance (EPR) measurements and nuclear magnetic resonance (NMR) measurements are reported for theS=10 single-molecule magnet Fe₈Br₈. We find that theS=10 state is nested with its first excited state, withS=9, located at only 24±2 K above. Also reported are some preliminary⁸¹Br NMR measurements of the unpaired electron spin density on the Br^? sites. The results provide new insight and benchmarks for improved electronic and magnetic structural calculations and macroscopic tunneling pathways of this class of single-molecule magnets.     

Infrared-microwave two-photon spectra of the ν3 bands of 12CH3F and 13CH3F

Infrared-microwave two-photon spectra have been obtained for the ν₃ bands of ¹²CH₃F and ¹³CH₃F with a two-photon spectrometer employing a CO₂ laser and a computer-coupled microwave source operating in the 8–18 GHz region. Even though the intensities of the spectra for the double parity levels in these molecules are inversely proportional to the square of the microwave frequency, transitions have been observed with microwave frequencies of up to 16 GHz. Comparison of these observed two-photon frequencies to frequencies predicted from infrared laser Stark spectroscopy, and to frequencies calculated from vibration-rotation parameters obtained by fitting these and other frequencies, shows agreement to within a few MHz. Spectroscopic parameters for the ground and ν₃ excited states of the two species are reported.     

Microwave optical double resonance of NO2 with a tunable cw dye laser: Spin-rotation and hyperfine interactions in the 2B2 excited electronic state

Various spin and hyperfine components of the 6₁₆ → 7₀₇ microwave transition in the ²B₂ electronic excited state were observed by microwave optical double-resonance spectroscopy using a tunable cw dye laser near 593 nm. Spin splittings and the hyperfine structure of two levels were precisely determined. Spin-rotation and hyperfine interactions in the ²B₂ state are discussed using these and the previously reported results on the 8₁₈ → 9₀₉ transition. From the hyperfine splittings of the K_a = 0, N = 7 and 9 levels, a value for the Fermi contact interaction constant, (0)_I, of ～50 MHz was determined.     

Optical detected ESR in the4 S 3/2 excited state of Er:YCl3

The electron spin resonance in the⁴ S _3/2 excited state of Er³⁺ in yttrium trichloride was studied by optical detection techniques. From angular dependence of the resonance field the principle value of theg-tensor in direction of the twofold crystal axis was deduced to beg∥=3.350±0.004 and the perpendicular valueg⊥ in the crystallographica-b-plane was extrapolated to beg⊥=2.857±0.004. The lifetime of the excited state is found to be temperature independent with τ _r =(1.62±0.02)·10^?3 sec and the spin lattice relaxation timeT ₁ was determined in the temperature region 1.5 to 2.1 °K by observing the recovery of the fluorescent light signal after a microwave saturation pulse was switched off.T ₁ is found to follow a direct process with \(T_1^{ - 1} = k \cdot cth\left( {\frac{{\rlap{--} h\omega }}{{2kT}}} \right)\) .     

Spectroscopic constants of the ground and lower vibrational states of CH2BrF: A combined high resolution infrared and microwave study

The enriched ⁸¹Br isotopic species of bromofluoromethane has been investigated in the infrared and microwave regions. The rovibrational spectrum of the ν₅ fundamental has been studied by high resolution FTIR spectroscopy, while the rotational spectra of the ground and v₆ = 1 states have been observed by means of microwave spectroscopy. More than 2700 transitions have been assigned in the ν₅ band and the analysis of the rovibrational structure reveals a first-order c-type Coriolis resonance with the v₆ = 2 state. The present study improves the ground state constants available in the literature and enables the determination of further centrifugal distortion parameters together with the full bromine quadrupole coupling tensor. A set of spectroscopic parameters up to the sextic distortion terms for the vibrational excited states has been accurately evaluated for the first time.     

Microwave spectrum and barrier to internal rotation of 1-chloro-2-butyne

Rotational transitions of the μ_a and μ_b type have been identified with microwave-microwave double resonance measurements for 1-chloro-2-butyne in the ground vibrational state. In the first excited state of the methyl torsion only μ_a-type transitions have been identified. The A-type transitions of the ground vibrational state can be described perfectly by the rigid rotor approximation with centrifugal corrections. Using the internal axis method the barrier to internal rotation was determined from the A,E splittings: V₃ = 10.05 ± 0.09 cm⁻¹. A model which allowed for geometry relaxation upon internal rotation was used to fit one set of parameters to the transition frequencies of both ground state and first excited torsional state. The sixfold contribution to the barrier was found to be negligible: V₆ = −0.4 ± 0.3 cm⁻¹.     

Lebensdauer des 5s5p 3 P 1-Zustands von Strontium

The lifetime of the 5s5p ³ P ₁ state of Sr has been determined with optical double resonance by observation ofrf-transitionsΔm _J =±1 between Zeeman levels of the even isotopes. The measurement yields the value τ(5³ P ₁, Sr)=2.1(3) · 10^?5 sec. A new type of narrowing of optical double resonance signals due to a time-of-flight effect of the radiating atom has been observed and compared with the theory.     

Linienform von Doppelresonanzsignalen bei zeitlich aufgelöster Beobachtung der zerfallenden Atomzustände

The influence on the line width and the line profile of optical double resonance signals due to a selective detection of quanta of resonance light emitted in a defined time interval after the moment of excitation has been studied. A narrowing of radio frequency signals in the5s 5p ³P₁ state of Cd by a factor of 1.4 has been observed. The resonance curves deviate considerably from the lorentzian line shape. Comparison has been made between the measured line profile and a theory developed for this experiment.     

BCl3振动激发弛豫的红外吸收研究

本工作用红外双共振技术测量了BCl₃分子的振动激发态吸收光谱。观察了分子间的多种弛豫过程及能量转移过程。得到关系式Pτ_V-V^(11BCl₃)=3微秒·托。观察到径向声波对双共振信号的调制,声速为2×10⁴厘米/秒,与计算值相符。 关键词：