Observation of the dynamic Stark effect at microwave frequencies in a molecular beam maser

Multiplet splitting of the main doublet of the ¹⁴NH₃, J = K = 1 inversion line has been observed in a molecular beam maser spectrometer when a strong microwave radiation field is introduced into the maser cavity. This phenomenon is attributed to the dynamic Stark effect at microwave frequencies.     

Determination of electric dipole moment for the ν2 vibrational state of 15NH3 by infrared-infrared double resonances

An infrared-infrared double-resonance technique, employing the sidebands produced by electro-optic amplitude modulation of a single-frequency CO₂ laser, is used to observe the second-order Stark effect of the ν₂asR(2, 0) transition of ¹⁵NH₃. The technique enables the Stark shifts in ground and vibrationally excited states to be observed separately and yields the electric dipole moments: μ(v₂ = 1) = 1.253 ± 0.003 D, μ(v = 0) = 1.469 ± 0.004 D. The relative intensity distribution, linewidths, and line shapes of features in the double-resonance Stark spectra are also examined.     

Dipole moment of the HO2 radical from its microwave spectrum

Stark effects are measured for the 1₀₁ ← 0₀₀, 7₁₇ ← 8₀₈, and 9₀₉ → 8₁₈ transitions of the HO₂ free radical. The unresolved Stark patterns of the b-type transitions are analyzed by the use of computer simulation. Second-order perturbation theory, including the effect of spin-doublings in the denominators, is used for the calculation of the Stark effect coefficients. The dipole moment determined is μ_a = 1.412 ± 0.033 D, μ_b = 1.541 ± 0.016 D, and μ_total = 2.090 ± 0.034 D.     

Saturated absorption Stark spectroscopy of CH3OH with CO2 lasers

The vibration-torsion-rotation spectrum of CH₃OH has been studied by saturated absorption spectroscopy in applied electric fields up to 20 kV/cm, using ¹²C¹⁶O₂ and ¹²C¹⁶O₂ lasers. Frequency offsets for 129 absorption lines were measured relative to the frequency of a fluorescence stabilized reference laser with an accuracy of ±0.5 MHz for 75 lines inside the ±40 MHz tuning range and 2–5% for lines located up to 1.2 GHz outside the tuning range, but Stark tuned into resonance. For 36 lines we obtained fully-resolved Stark spectra, allowing determination of both lower and upper state K. Using this information in combination with information available from optically-pumped FIR laser emission, a total of 44 lines were completely assigned as transitions involving torsional n = 0, 1, 2 and 3 states of the CO stretch. Certain states belonging to n = 1 displayed an anomalous Stark effect which is at present not understood.     

Laser stark spectroscopy ofSO2 with the HCN laser

The Far Infrared (FIR) laser Stark spectrum ofSO ₂ was investigated using the 337 m line of the HCN laser. Two distinct families, one originating at low field and the other at high field, were observed. The high field transition is identified as theJ _K–1,K+1=22_5,1721_4,18, v₂=1 transition. A significant fourth-order Stark shift was observed for this transition in the presence of a large second-order Stark shift. The zero-field frequency of the assigned transition was obtained by accounting for the fourth-order contribution.Present Adress: Department of Chemistry, University of Rochester, Rochester, NY 14627.     

Microwave l-type resonance transitions of the v4 = 1 state in PF3: Detailed interactions and molecular structure

Observation of the direct l-type resonance transitions in the microwave spectrum of the v₄ = 1 state of PF₃ has been extended to J = 36. The w-type interaction, (Δl = 0, ΔK = 6), has been found from measurements on the “forbidden” Stark trasitions in the $\text{K}\text{= 3}$ series. Also in this series a close accidental degeneracy was found between J = 30, $\text{K}\text{= 3}$ and 0, leading to new zero-field “forbidden” transitions through the r-type interaction (Δl = 2, ΔK = ?1) and to the determination of the C rotational constant. Nine spectroscopic parameters were determined using 140 observed frequencies including two “forbidden” trasitions. After suitable correction the B and C constants were used to determine the r₀, r_z, and r_e structures for PF₃. The equilibrium structure is estimated to be P-F = 1.561 ± 0.001 Å and ∠FPF = 97.7 ± 0.2°.     

Laser Stark and laser-microwave double-resonance spectroscopy of the ν2 band of CD3I

The ν₂ fundamental band of CD₃I was investigated by means of the laser Stark spectroscopy using a 10.6 μm CO₂ laser and an N₂O laser as infrared radiation sources. The assignment was established for about 150 Stakr resonances. Laser-microwave double resonance was used to confirm the assignment. A least-squares analysis of the Stark spectrum gave the molecular constants: μ″ = 1.6504 ± 0.0004 D; μ′ = 1.6479 ± 0.0005 D; ν₀ = 28 461 093.8 ± 3.6 MHz; A′ - A″ = 234.0 ± 1.1 MHz; D_K′ - D_K″ = 0.121 ± 0.085 MHz. The uncertainties are 2.5 times the standard deviations. The single and the double primes refer to the ν₂ and the ground vibrational states, respectively.     

The ν2 fundamental band of H2CO

The ν₂ fundamental band of H₂CO has been studied using a combination of sub-Doppler laser Stark spectroscopy and Doppler-limited Fourier transform spectroscopy. A combined analysis of the Stark and Fourier infrared data together with previous microwave data on the ν₂ = 1 state yielded improved molecular parameters for formaldehyde, including the excited state dipole moment. A small perturbation was noted at K′_a = 7 which may be ascribed to a ΔK_a = 2 interaction with the v₃ = 1 state. Precise treatments of ν₂ with K′_a > 6 will thus require a combined analysis taking into account Coriolis interactions among ν₄, ν₆, ν₃, and ν₂.     

The Stark and Zeeman effects in methyl silane

The Stark and Zeeman effects in methyl silane in the ground vibronic state have been studied in detail using the molecular-beam electric-resonance method. For a symmetric rotor without internal rotation, the rotational dependence of the effective dipole moment for matrix elements diagonal in J has been shown by Watson, Takami, and Oka to have the form μ_Q = μ₀ + μ_JJ(J + 1) + μ_KK². It is shown here that, to this order, a complete characterization of the Stark effect requires only one more parameter, namely, the effective anisotropy (α_| - α_⊥)_eff in the polarizability. From Stark measurements alone, the true anisotropy cannot be separated from the additional dipole distortion constant shown by Aliev and Mikhaylov to enter dipole matrix elements off-diagonal in J. By studying nine different transitions (J, K, m_J) → (J, K, m_J ± 1) in CH₃²⁸SiH₃, values were obtained for the four Stark parameters: μ₀ = 0.7345600(33) D, μ_J = 8.83(35) μD, μ_K = ?32.82(37) μD, and (α_| - α_⊥)_eff = 1.99(16) × 10^?24 cm³. These errors reflect only the internal consistency in the data; the absolute error in μ₀ is 32 μD. The modification of the Stark effect by internal rotation is discussed; it is shown that the only significant effect here is to modify the interpretation of μ₀. The change in μ₀ upon isotopic substitution of ³⁰Si for ²⁸Si was determined: $\text{μ}{}_0\text{(}{}^{30}\text{Si) - μ}{}_0\text{(}{}^{28}\text{Si) = 67.0(2.0) μD}$. A study of molecular magnetic effects in CH₃²⁸SiH₃ has yielded the two molecular g factors, g_⊥ = ?0.036391(21) nm and g_| = ?0.10667(13) nm, as well as the anisotropy in the susceptibility $\text{(χ}{}_{\mathrm{|}}\text{- χ}{}_{\mathrm{\perp }}\text{) = ?44.9(2.3) × 10}{}^{\mathrm{?30}}\text{J}\text{T}{}^2$. The molecular quadrupole moment has been calculated.     

The electric dipole moment of methyl fluoride

The Stark effect of CH₃F is extensively used as a calibration standard in laser Stark spectroscopy. The accepted value for the dipole moment of the ground vibrational state of CH₃F is less accurate than the precision of laser Stark measurements, and questions have also been raised about the literature value. New molecular beam spectroscopy measurements have been made of the ratio of the Stark effect in the J = 1, K = 1 and J = 2, K = 2 CH₃F states to that of the 01¹0 vibrational state of OCS. The results were $\text{μ}{}_{1.1}\text{(}\text{CH}{}_3\text{F}\text{)}\text{μ}{}_{010}\text{(}\text{OCS}\text{)}\text{= 2.638905(23)}$ and $\text{μ}{}_{2.2}\text{(}\text{CH}{}_3\text{F}\text{)}\text{μ}{}_{010}\text{(}\text{OCS}\text{)}\text{= 2.63894(10)}$. This produces a dipole moment of 1.85840 D with precision relative to OCS of 10 ppm and absolute accuracy of 43 ppm.     

Line-mixing between rotational Stark components of CH3F self-perturbed and perturbed by helium: Experimental results and IOS analysis

Self- and He-broadening coefficients of microwave transitions of CH₃F have been measured with and without the presence of an external electric field. This provides values for the J, K → J + 1, K (K = 0 − J) transitions for J = 1 and J = 3 as well as for the various J, K, M → J + 1, K, M′ (|M| = 0 − K, |M - M′| = 0, 1) Stark components. The results and those of a previous experimental study for pure CH₃F, which show significant line-mixing effects, are analyzed with a model based on the Infinite Order Sudden approximation. It is shown that the latter leads to very satisfactory modeling of observed values even though no parameter was adjusted since previously and independently determined basic cross-sections are used. The quality of the present predictions is comparable with that obtained previously with a semi-classical approach. Furthermore, it is shown that the previously stated inaccuracy of the IOS model was due to an oversimplified use of this approach.     

Stark spectroscopy of 13CD3OH with the HCN laser

The laser Stark spectrum of ¹³CD₃OH has been studied using the 311 μm line of the HCN laser. An extensive series of absorption lines has been observed and assigned to the J = 3 to 11 members of the K = 2 ← 3E₁, Q-branch transition in the v_t = 1 excited torsional state. Zero-field frequencies for all the assigned transitions are given with improved accuracy over those calculated from available molecular constants. For the Q-branch series, the branch origin and the series expansion coefficients are also presented.     

Microwave spectroscopy of propynal in the v2 = 1 vibrational state by IR-MW triple resonance

Infrared-microwave triple resonance was applied to microwave spectroscopy of propynal, HCCCHO, in the v₂ = 1 vibrational state. Eleven microwave transitions were newly observed by using a Zeeman-tuned 3.51 μm HeXe laser as the infrared radiation source. The spectrum was analyzed including the 11 transitions previously observed by double resonance. A least-squares fit of the 13 low-J transitions revealed that the rotational constants in the K_?1 = 1 states were slightly different from those of the K_?1 = 0 states. A higher-order rotational resonance was proposed for explanation of the effect.     

ΔK = 2 transitions in H2CO and D2CO

Weak transitions of the type ΔJ = ± 1, $\text{Δ}\text{K}{}_{\mathrm{a}}\text{= ? 2}$, ΔK_c = ± 3 have been observed in H₂CO and D₂CO by the millimeterwave double resonance method and also by direct absorption with a Stark modulated spectrometer. The addition of these new transitions in a least-squares analysis, in which all previously known microwave and millimeterwave data are also included, results in an improved set of rotational and distortion constants.     

Measurement of the electric dipole moment of NO (X2 Π ν = 0,1) by mid-infrared laser magnetic resonance spectroscopy

A pair of parallel Stark plates are added to a CO laser magnetic resonance spectrometer to apply electric field in the absorption cell. This apparatus is used to measure the molecular electric dipole moment via Zeeman and Stark effects simultaneously. The saturated absorption spectra of NO (X²Π_3/2, ν = 1 ← 0) was observed and the electric dipole moments of NO were directly measured in the presence of an electric field. The dipole moments are determined as μ₀(ν = 0) = 0.1595(15) D, μ₁ (ν = 1) = 0.1425(16) D. The electric dipole moment of the vibrationally excited state (ν = 1) is determined for the first time. The dependence of the electric dipole moments on its nuclear distances is interpreted.     

Effects of radiator motion on plasma-broadened hydrogen lyman-β

For the hydrogen line L-β, broadening in an Ar⁺-plasma (N_e = 7.2 × 10¹⁶ cm^?3, T = 12,200 K) has been investigated with the help of a computer simulation of ion broadening taking full account of radiator motion. The anisotropy in Stark broadening for a moving radiator is found to be negligible under these conditions, but Stark profiles depend markedly on the radiator speed. The final line profile (including Stark and Doppler broadening) is nearly the same as the profile obtained by convolution of the Doppler profile with the Stark profile for radiators at rest and fictitious ions with the reduced mass of the atom-ion pair.     

Millimeter wave spectrum of acetonitrile oxide,CH3CNO,in the ν10 vibrational manifold: The ground state and the state v10 = 1

The pure rotational spectrum of CH₃CNO was measured in the frequency range 75 to 230 GHz. For the ground state, transitions were measured for J between 9 and 28 and for K from 0 to 12. In the v₁₀ = 1 state the measurements range from J = 0 to 19 and from K = 0 to 11. Numerous perturbations are observed, apparently due to accidental resonances with levels in other vibrational states. The contributions due to ΔK = 2, Δl = 2 matrix elements (l-type resonance and l-type doubling) are accounted for by matrix diagonalization, and the effects due to accidental resonances are presented graphically.     

Theoretical Study of the Dynamic Stark Effect on Dissociation of CsI

The influence of the dynamic Stark effect on the dissociation of CsI is theoretically studied by the time-dependent wave-packet method. After a pump pulse induces a dissociating wave packet that propagates through both the ionic channel X0⁺(Cs ⁺(¹ S ₀)?+?I ⁺(¹ S ₀)) and the covalent channel A0⁺(Cs(² S _1/2)?+?I(² P _3/2)), a Stark pulse is applied to control the diabatic-dissociation dynamics. The first-order non-resonant non-perturbative dynamic Stark effect gives control over the break up, the dissociation probabilities in the two channels being controlled by the delay between the pump and Stark pulses. With a 720-fs delay, the dissociation probability through channel A is greatly enhanced.     

Use of the anomalous Stark effect for the approximate determination of torsional energy splittings

An advantageous use of the anomalous Stark effect for the determination of the torsional energy splittings is proposed. The method is applicable in those cases where the dipole moment component connecting the torsional states of different parity has an experimentally observable magnitude. The analysis of the Stark spectrum observed in the spectrum of the N-cis lone-electron-pair gauche isomer of allylamine is presented as an example. The Stark effects of those transitions (a-type and b-type) which are inside the same vibrational state (0⁺ and 0^?), are used for the fitting of the μ_a, μ_b, and μ_c dipole moment components as well as the torsional energy splitting Δν_tors. The values obtained are compared to more accurate values derived by other methods. The possible use for predicting large torsional splittings is discussed.