M-dependence of collisional transfer of rotational energy in OCS mixtures

Collision-induced transitions between rotational levels of OCS in the ground vibrational state have been investigated by steady-state microwave double resonance, with the M sublevels separated by a Stark field. The (2 ← 1)_P-(1 ← 0)_S, (3 ← 2)_P-(1 ← 0)_S, and (4 ← 3)_P-(1 ← 0)_S systems have been studied for pure OCS and for mixtures with excess CH₃OH, He, and H₂. For four-level systems having dipolar connections (ΔJ = 1; ΔM = 0, ± 1; parity ± ? ?) between pump and signal levels, it is found for OCS and the OCS-CH₃OH mixture that the dipole-type ΔJ = 1 transitions always dominate the collisional transfer, but for the OCS-He and OCS-H₂ mixtures that ΔJ = 2 quadrupole-type transitions are dominant. For all four collision partners, significant ΔJ = 2 and ΔJ = 3 collisional transfer is observed in some systems, indicating the presence of high-order terms in the collisional interaction.     

Experimental microwave collision diameters in the rotational spectrum of H2CO

Collision diameters for some select transitions in the rotational spectrum of H₂CO have been determined using pressure broadening of the spectral lines. Transitions of the type ΔJ = 0, K_?1 = 1, and ΔK₊₁ = 1 with 1 ≤ J ≤ 5 were investigated for both self-broadening and foreign gas broadening (He and H₂) of the spectral lines. Pressure ranges from 0.001 Torr to 0.1 Torr were explored in obtaining the line width parameters Δν_p for each transition. Collision diameters were found to be very nearly constant (14 Å) over the J states studied for H₂COH₂CO interaction, 2.5–5.8 Å for H₂COH₂ interaction and 2.7–3.5 Å for H₂COHe interaction.     

The microwave spectrum and structure of chloromethyl cyclopropane

The microwave spectra of $\text{CH}{}_2\text{CH}{}_2\text{CH}$CH₂³⁵Cl and $\text{CH}{}_2\text{CH}{}_2\text{CH}$CH₂³⁷Cl have been observed and lines assigned to the gauche form. The rotational constants in MHz and distortion constants in KHz are: C₃H₅CH₂³⁵Cl, A = 11745.65, B = 2047.274, C = 1886.622, Δ_J = 0.85, Δ_JK = ? 0.9, Δ_K = 44., δ_J = ? 0.099, δ_K = 19.1, C₃H₅CH₂³⁷Cl, A = 11691.61B = 1997.664, C = 1842.823, Δ_J = 0.7, Δ_JK = ? 64.6, Δ_K = 2400, δ_J = 0.19, δ_K = ? 67.     

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.     

Pressure-induced H2 opacity in the 5-μm region

The H₂ opacity arising from the pure-rotational hexadecapole-induced U₀(J) transitions occurring during H₂H₂ and H₂He collisions, and from the hexadecapole-induced U₀(J) + S₀(J′) and the quadrupole-induced S₀(J) + S₀(J′) transitions in H₂He collisions, has been calculated. The U₀(J) and S₀(J) + S₀(J′) contributions from H₂H₂ collisions are important H₂ opacities in the frequency range from 700–3000 cm^?1 for temperatures appropriate to the outer planets. It is concluded that this opacity is needed in addition to the opacity from the extrapolation of the 0-0 and 1-0 H₂H₂ collisionally induced bands to interpret the spectrum at 5 μm for the outer planets.     

Laser Stark measurements on OCS including the observation of zero-field-forbidden ΔJ = 0, ±2 transitions

Laser Stark measurements have been made on the 02⁰000⁰0 and 03¹001¹0 vibrational transitions of ¹⁶O¹²C³²S, ¹⁶O¹²C³⁴S, and ¹⁸O¹²C³²S, and on the 03¹001¹0 transition of ¹⁶O¹³C³²S, using a CO₂ laser. In addition to providing dipole moment information for excited vibrational states, these measurements give vibrational band centers accurate to several megahertz. To aid in optical pumping experiments, several near coincidences between CO₂ laser transitions and OCS absorption lines are discussed. Electric-field-allowed ΔJ = 0 transitions are observed for the 2ν₂ band of ¹⁶O¹²C³²S and ¹⁶O¹²C³⁴S, as well as ΔJ = 2 transitions for the same band of ¹⁸O¹²C³²S.     

The microwave spectra and structures of epihalohydrins: Epichlorohydrin

The microwave spectrum of the two chlorine isotopic species of epichlorohydrin ($\text{CH}{}_2\text{OCH}$CH₂Cl) is reported. The structure is a gauche conformation with the Cl atom twisted toward the oxygen side of the ring. The observed rotational constants (in MHz) and centrifugal distortion constants (in kHz) are: C₂H₃OCH₂³⁵Cl; A = 13 373.02, B = 2080.353, C = 1932.469, Δ_JK = ? 6, Δ_K = 2400, δ_J = ? 0.43, δ_K = 17, H_KJ = ? 0.13, H_K = 570, h_JK = 0.061, h_K = ? 5.1: C₂H₃OCH₂³⁷Cl; A = 13 361.24, B = 2028.853, C = 1887.990, Δ_JK = 0.31, Δ_K = 1669., δ_J = ? 0.16, δ_K = 54.1.     

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.     

The heat capacity of the layer compounds (CH3CH2CH2NH3)2MnCl4 and (CH3CH2CH2NH3)2CdCl4 from 10 K TO 300 K

The heat capacity of the layer compounds tetrachlorobis (n-propylammonium) manganese II and tetrachlorobis (n-propylammonium) cadmium II, (CH₃CH₂CH₂NH₃)₂MnCl₄ and (CH₃CH₂CH₂NH₃)₂CdCl₄ respectively, has been measured over the temperature range 10 K ?T ? 300 K.Two known structural phase transitions were observed for the Mn compound in this temperature region: at T = 112.8 ± 0.1 K (ΔH_t= 586 ± 2 J mol^?1; ΔS_t = 5.47 ± 0.02 J K^?1mol^?1) and at T =164.3 ± (ΔH_t = 496 ± 7 J mol^?1; ΔS_t =3.29 ± 0.05 J K^?1mol^?1). The lower transition is known to be from a monoclinic structure to a tetragonal structure, while the upper is from the tetragonal phase to an orthorhombic one. From comparison with the results for the corresponding methyl Mn compound it is deduced that the lower transition primarily involves changes in H-bonding while the upper transition involves motion in the propyl chain.A new structural phase transition was observed in the Cd compound at T= 105.5 ± 0.1 K (ΔH_t= 1472.3 ± 0.1 J mol^?1; ΔS_t = 13.956 ± 0.001 J K^?1mol^?1), in addition to two transitions that have been observed previously by other techniques. The higher of these transitions(T = 178.7 ± 0.3 K; ΔH_t = 982 ± 4 J mol^?1 ΔS_t = 6.16 ± 0.02 J K^? mol^?1) is known to be between two orthorhombic structures, while the structural changes at the lower transition (T= 156.8 ± 0.2 K; ΔH_t = 598 ± 5 J mol^?1, ΔS_t = 3.85 ± 0.03 J K^?1 mol^?1) and at the new transition are not known. It is proposed that these two transitions correspond respectively to the tetragonal to orthorhombic and monoclinic to tetragonal transitions in the propyl Mn compounds.In addition to the structural phase transitions (CH₃CH₂CH₂NH₃)₂MnCl₄ magnetically orders at t? 130 K. The magnetic contribution to the heat capacity is deduced from the heat capacity of the corresponding diamagnetic Cd compound and is of the form expected for a quasi 2-dimensional Heisenberg antiferromagnet.     

Calculated vibrational transition probabilities of OH(X2Π)

The theoretically derived dipole moment function of OH(X²Π) obtained by Stevens Das, Wahl, Neumann, and Krauss is used to calculate the absolute intensities of the vibrational-rotational transitions of the OH Meinel bands. The calculations take full account of the spin uncoupling and vibration-rotation coupling which markedly influence the radiative transition probabilities. The effect of lambda-doubling on the vibrational transitions is analyzed and generally found to be negligible. Results are tabulated for Δv = v′ – v″ ranging from the fundamental transitions Δv = 1 to the Δv = 5 overtone, for v′ = 1–9 and J′ = 0.5 – 15.5. A comparison is made with available data, and various features of the OH spectrum are examined that are of aeronomical and experimental interest. Thermally averaged emission rates are presented for Δv = 1–5, and the validity of the rotational temperatures commonly derived from experimental intensity distributions is questioned.     

Inversion-rotation spectrum and spectroscopic parameters of 14ND3 in the ground state

The far-infrared spectrum of ¹⁴ND₃ has been recorded in the region between 30 and 220 cm^?1 at a resolution, before deconvolution, of approximately 0.004 cm^?1. ΔJ = +1, ΔK = 0, a ← s and s ← a inversion-rotation transitions have been measured and assigned up to J″ = 19. These transitions, the pure inversion-microwave transitions and ground-state combination differences from the analysis of the ν₂ and ν₄ bands have been fitted simultaneously to an inversion-rotational Hamiltonian which includes Δk = ±3 and Δk = ±6 interaction terms. The ground-state spectroscopic parameters obtained in this way reproduce the transition frequencies within the accuracy of the measurements.     

Adsorption of water and methanol on GaAs(110) surfaces studied by ultraviolet photoemission

UV photoemission spectroscopy (UPS) with He 1 radiation (hν = 21.2 eV) has been used to study the interaction of H₂O and CH₃OH with GaAs(110) surfaces prepared by cleavage in ultrahigh vacuum (UHV). For H₂O two molecularly adsorbed phases can be distinguished at 300 K: at low coverage H₂O is chemisorbed by its oxygen lone-pair orbital to the surface whereas for higher exposures a less perturbed species which resembles more a “physisorbed” or condensed H₂O layer is found. At 180 K only the less perturbed species can be identified. Also CH₃OH is chemisorbed molecularly at lower coverage with its oxygen end to the GaAs surface. For higher exposures two additional emission bands are observed which are interpreted as due to the methoxy radical CH₃O resulting from a partial decomposition of CH₃OH.     

Pressure broadening of the ground vibrational state J = 31→J = 32 transition of CH3F by coincidence laser spectroscopy

We have studied self-broadening and foreign gas broadening of the ground state J = 31→J = 32 transition of CH₃F using a coincidence with the 184.3 μm emission from an optically pumped CH₂F₂ laser. Experiments have been carried out with polar and non-polar species as well as the noble gases.This transition is in the region where the classical rotation period is of the same order as the duration of a collision. The measurements indicate an anomalously low value of 7.0 MHz/Torr for the self-broadening coefficient of CH₃F and an unusually large value for the CH₃OH broadening coefficient. The latter is believed to be due to the presence of a low energy OH torsional model in CH₃OH.     

Doppler-shift of fourth sound in flowing 3He4He mixtures

The Doppler-shift Δu₄ of fourth sound propagating in flowing superfluid ³He⁴He mixtures is calculated for arbitrary ³He concentration c. For c ? 0.15 and at T ? 1.4 K a cancellation of the dominant terms in the equation for Δu₄ results in a concentration independent shift.     

The heat capacity of the layer compound tetrachlorobis (methylammonium) manganese—II (CH3NH3)2MnCl4, from 10 to 300k

The heat capacity of the layer compound, tetrachlorobis (methylammonium) manganese II, (CH₃NH₃)₂MnCl₄, has been measured over the range 10K <T<300K. In this region, two structural phase transitions have been observed previously by other techniques: one transition is from a monoclinic low temperature (MLT) phase to a tetragonal low temperature (TLT) phase, and the other is from TLT to an orthorhombic room temperature (ORT) phase. The present experiments have shown that the lower transition (MLT→TLT) occurs at T = 94.37±0.05K with ΔH_t = 727±5 J mol^?1 and ΔS_t = 7.76±0.05 J K^?1 mol^?1, and the upper transition (TLT→ORT) takes place at T = 257.02±0.07K with ΔH_t = 116±1J mol^?1 and ΔS_t = 0.451±0.004 J K^?1mol^?1. These results are discussed in the light of recent measurements on (CH₃NH₃)₂CdCl₄, and also with regard to a recent theoretical model of the structural phase transitions in compounds of this type.In addition to the structural phase transitions, (CH₃NH₃)₂MnCl₄ also undergoes magnetic ordering at T < 150K. The magnetic component to the heat capacity, as deduced from a corresponding states comparison of the heat capacity of the present compound with that of the Cd compound, is shown to be consistent with the behaviour expected for a quasi 2-dimensional Heisenberg antiferromagnet.     

Far infrared spectrum and spectroscopic constants of AsH3 in the ground state

The far ir spectrum of arsine, AsH₃, was recorded in the range 25–100 cm^?1 with a resolution of approximately 0.004 cm^?1. ΔJ = +1, ΔK = 0 rotational transitions were measured and assigned up to J″ = 12. These transitions, together with the presently available microwave and submillimeter-wave data and ground state combination differences, were analyzed on the basis of a rotational Hamiltonian which includes Δk = ±3 and Δk = ±6 interaction terms. The derived ground state molecular parameters reproduced the transition frequencies of both allowed and “perturbation allowed” transitions within the accuracy of the measurements. The equilibrium structure was determined for the AsH₃ molecule.     

Infrared-radio frequency double resonance observations of pure rotational Q-branch transitions of methane

The $\text{F}{}_2{}^{\mathrm{(2)}}\text{← F}{}_1{}^{\mathrm{(2)}}$ and $\text{F}{}_2{}^{\mathrm{(2)}}\text{← F}{}_1{}^{\mathrm{(1)}}$ transitions of the J = 7 levels of the ground state of CH₄ have been observed by infrared-radio frequency double resonance using the 3.39 μ HeNe laser line. The transition frequencies are 423.02 ± 0.02 MHz and 1246.55 ± 0.02 MHz, respectively. Using these frequencies and the splitting of the E and F₂ levels of the J = 2 state calculated from the molecular beam magnetic resonance spectra of Ozier, the centrifugal distortion constants are derived to be D_t = 132933 ± 10 Hz, H_4t = ? 16.65 ± 0.2 Hz, and H_6t = 10 ± 1 Hz. The J = 15 E⁽¹⁾ → E⁽²⁾ microwave transition is predicted as 14150 ± 9 MHz.     

A model for high-spin/low-spin transitions in solids including the effect of lattice vibrations

A model for high-spin/low-spin transitions in solids is discussed including the effect of low symmetry ligand fields and spin-orbit coupling. These interactions are required in the calculation of quadrupole splitting and magnetic susceptibility. In addition, the contribution from lattice vibrations is taken into account within the approximation of the Debye model. The recently observed entropy change at the transition temperature may be easily explained on this basis. The model is applied in a detailed numerical fit of the experimental data of [Fe(4,7-(CH₃)₂-phen)₂(NCS)₂] where phen = 1,10-phenanthroline. The compound may be characterized by the parameter values Δ₁, = Δ₂ = 400 cm^?, λ = ?80 cm^?1, J = 196 cm^?1 (or J_tot = 205 cm^?1) and N = 10 experimentally based Debye temperatures Θ₁ = 140 K and Θ_h = 130 K have been employed.     

The pure rotational Raman spectrum of CS2 in the ground and 010 vibrational states

The pure rotational Raman spectra of CS₂ in the 00⁰0 and 01¹0 vibrational states have been observed using a low power HeNe laser (λ = 6328 Å) and a high resolution plane grating spectrograph. The ΔJ = 2 transitions with J = odd in the 01¹0 state are clearly resolved from the ground state transitions thus allowing the determination of some upper state rotational constants. The molecular constants determined in this work are for the 00⁰0 ground state, B_00⁰0 = 0.10912 ± 0.7 × 10⁻⁵ cm⁻¹, (D_J)_00⁰0 = (0.83 ± 0.18) × 10⁻⁸ cm⁻¹ and for the 01¹0 excited state B_01¹0^c = 0.10935 ± 0.00002 cm⁻¹ and (D_J)_01¹0^c = (1.5 ± 0.6) × 10⁻⁸ cm⁻¹.     

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.