High order vibrational matrix elements for diatomic molecules; dipole moment function and transition moments of CO

The fifth and sixth-order contributions to the vibrational matrix elements are obtained for the transitions v→v'(v'?v+4) using an eight power internuclear Dunham potential and a quartic power series expansion of the dipole moment function. The results for the dipole moment coefficients M₀ to M₄ of CO and the transition moments R_v^v' (with v=5, 10, 20) deduced from a calculation including succesively third, fourth, fifth and sixth-order perturbation theory are compared. The validity of these results is discussed.Using a quintic dipole moment function, general expressions for the vibrational matrix elements corresponding to the transitions v→v'(v'? v+5) are also presented and the influence of these contributions on the calculation of the dipole moment coefficients as well as the hot band transition moments of CO is shown.     

High-resolution laser Stark and Fourier transform spectroscopy of DBr at 5.5 μm

A very close coincidence between the P(1) transition of the 1-0 band of D⁷⁹Br and a CO laser line has allowed the observation of a DBr laser Stark spectrum. The observed inverse Lamb dips resolve the Br hyperfine structure of the transition, and are used to determine the value of the dipole moment of DBr in the v = 1 state. A high-resolution Fourier transform spectrum of DBr in the region 1750 to 1900 cm^?1 has also been recorded and accurately measured. These new data, together with the best previous microwave and infrared measurements, are used to determine molecular parameters for DBr, and also result in improved secondary wavenumber standards for the 5.5-μm region.     

Infrared tunable diode laser spectra of lithium fluoride at high temperatures

At temperatures up to 1300 K the high resolution spectrum has been measured for the 1-0 through 7-6 vibrational transitions of ⁷LiF and the 1-0 through 8-7 vibrational transitions of ⁶LiF. These infrared ro-vibrational measurements have been combined with microwave measurements taken from the literature to obtain a set of ten Dunham potential constants that reproduce all the measurements for both isotopic species to within their experimental uncertainty. The band center for the v = 1-0 transition is 894.34104±0.00020 cm^?1 for ⁷LiF and 946.12074±0.00024 cm^?1 for ⁶LiF.     

The forbidden (J → J + 1) spectrum of CH4 in the ground vibronic state

The pure rotational R-branch spectrum of CH₄ arising from the centrifugal distortion moment has been studied using a simple 12.10-m light-pipe cell and a conventional interferometer. Ten forbidden (J → J + 1) transitions for J = 7 to J = 16 have been observed in the spectral region 80–200 cm^?1 with a theoretical resolution of 0.5 cm^?1. The integrated intensity of the six strongest lines has been measured and was found to be of the order of twice that calculated from the distortion moment obtained earlier from a molecular beam study of the (J = 2) rotational level. In the approximation that frequency shifts due to this excess intensity are neglible, it has been determined that the rotational constant B₀ = (5.245 ± 0.004) cm^?1 and the scalar distortion constant D_S = (1.19 ± 0.09) × 10^?4 cm^?1. It is argued that the excess intensity is due to higher-order terms in the dipole moment operator and the validity of the frequency analysis is considered in this context.     

Infrared tunable diode laser spectroscopy of the Δv = 2 band of 7Li127I

The high-resolution infrared spectrum of the Δv = 2 transitions of ⁷LiI has been measured at temperatures near 1050 K. The observations include vibrational transitions ranging from 2-0 to 10-8. The data were fit to a set of Dunham potential constants complete through the a₆ term, from which the Dunham rovibrational constants were calculated. The band centers for the v = 1-0 and v = 2-0 transitions were determined to be 491.17398 ± 0.00026 cm⁻¹ and 976.73042 ± 0.00038 cm⁻¹, respectively.     

Infrared spectrum of boron chloride (BCl)

The spectrum of the Δv = 1 band of BCl was measured between 828 and 870 cm^?1 with a tunable diode laser. The absorptions of the v = 1-0, 2-1, 3-2, and 4-3 transitions of BCl were observed in both a microwave discharge and a dc discharge through BCl₃. Spectra of ¹¹B³⁵Cl, ¹¹B³⁷Cl, ¹⁰B³⁵Cl, and ¹⁰B³⁷Cl were observed in natural abundance. A set of eight Dunham coefficients was determined by fitting the data for all observed isotopic species with the appropriate reduced mass factors. A BCl bond distance, r_e = 0.1715283(31) nm, was determined which agrees with the value derived from the electronic spectrum of BCl. The band center for the v = 1-0 transition of ¹¹B³⁵Cl is ν₀ = 829.4087(8) cm^?1.     

The dipole moment of the FO radical

The electric dipole moment of the FO radical (${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$) has been directly measured by observing its saturated absorption laser magnetic resonance spectrum (v = 1 ← 0) in the presence of a moderate electric field. The resulting dipole moment [μ(v = 0) = 0.0043(4) D, μ(v = 1) = 0.0267(9) D] is extremely small, and shows a large relative change with vibrational state. The sign of the dipole moment is the same for the two vibrational states. Previous failures to detect microwave or gas phase EPR spectra of FO are fully explained by this small dipole moment.     

New measurements and global analysis of chloromethane in the region from 0 to 1800 cm

New high resolution Fourier transform spectra of pure ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl isotopomers of chloromethane have been recorded in Wuppertal covering the region from 600 to 3800 cm⁻¹. New rotational transitions within the v₂=1, v₅=1, and v₃=2 states have been measured at Lille. A first global analysis of the lower four band systems of the molecule (700-1800 cm⁻¹) is reported. The model was based on an effective Hamiltonian and dipole moment expressed in terms of irreducible tensor operators. A common set of 125 effective hamiltonian parameters (sixth order) has been adjusted to fit simultaneously some 11 000 IR data for each of the isotopomers including 153 mm wave data for 12CH₃35Cl. The assignments involve 12 sets of transitions (6 cold bands, 3 hot bands, and 3 pure rotational systems for ¹²CH₃³⁵Cl). The standard deviation was on average 0.00014 cm⁻¹ and 175 kHz for the IR and MMW data, respectively. The v₃=v₆=1 state was analysed for the first time principally from observed hot band transitions.     

Ring puckering in five membered rings: The microwave spectrum,dipole moment and barrier to pseudorotation in 1,3-dioxolane

The microwave spectrum of 1,3-dioxolane was investigated in the region 8–35 GHz. Nine vibrational states were assigned which indicated that the molecule undergoes pseudorotation. The dipole moment for each vibrational state was measured and found to be constant within experimental error at 1.19 ± 0.03 D. The lowest energy pair of vibrational states were found to be connected by rotation vibration transitions. The splitting of this pair was found to be 64 840.65 MHz with a perturbation element 435 ± 30 MHz. From the variation in the rotational constants, the far-infrared data, and the v = 0, 1 splitting the Hamiltonian for pseudorotation was found. Hφ=3.99Pφ±5.1(1-cosφ)?20.01(1?cos2φ).The phase of the potential function was determined from relative intensity measurements to be such that the maximum in the potential energy is at the twisted configuration with the bent configuration being 10.2 cm^?1 lower in energy.     

Spectral and luminescent properties of jet-cooled dinaphthofuran

The fluorescence and fluorescence excitation spectra of jet-cooled dinaphtho[2,1-b:1′,2′-d]furan (dinaphthofuran) molecules, as well as their complexation with inert gases Ar, Kr, and Xe, are studied. The indicatrices of the degree of polarization of fluorescence of dinaphthofuran molecules upon excitation of the electronic transitions S ₀?S ₁ and S ₀?S ₂ are calculated as functions of the intramolecular orientation of the transition dipole moments. The fluorescence polarization spectrum is measured under excitation within the rotational contour of the line of the purely electronic transition v ₀ ⁰ = 29 294 cm^?1. In contrast to complex planar molecules, the S ₀?S ₂ fluorescence excitation spectrum of dinaphthofuran is found to be continuous, with the Q branch of the rotational contour being absent. The fluorescence excitation spectra of van der Waals complexes of dinaphthofuran with inert gases exhibit multiplet lines, which is associated with the helical structure of the molecules studied.     

CP noninvariance and the possibility of a sizable neutron electric dipole moment

The electric dipole moment of the neutron will be measured to a precision of 10^?25 e-cm in the near future. We explore a new theoretical possibility that P and CP noninvariance leads to a sizable electric dipole moment. We calculate an electric dipole moment of about 10^?25 e-cm. In this phenomenological theory, we calculate CP-violating observables in non-leptonic decays from theK ⁰ ? \(\bar K^0 \) ,Λ ⁰ ?Λ ⁰ andK ⁺?K ^? systems. In connection with CP noninvariance, the possible observable occurrence of ΔS=2 decays is discussed. We calculate possible branching ratios; in particular that forΞ ⁰ → π^? p can be as high as about 10^?6. The possible existence of a weakly interacting, neutral scalar boson, which violates P and CP in the course of its propagation as a virtual particle, is considered.     

Difference frequency laser spectroscopy of the v = 1 ← 0 transition of NH

The v = 1 ← 0 vibration-rotation band of NH was observed with a difference frequency laser and a long-path, Zeeman-modulated discharge cell. The 29 transition wavenumbers (from P(4) to R(5)) were measured with an estimated accuracy of 0.003 cm^?1. The band origin (3125.5724 ± 0.0020 cm^?1) as well as the spin-spin, the spin-rotation, and the rotational constants were determined in a least-squares fit.     

Nonempirical and quasi-classical approaches to the calculation of the electronic transition dipole moments

The dependence of the electronic transition dipole moment on the internuclear separation is calculated nonempirically for the Meinel band of the N ₂ ⁺ molecular ion using the Gaussian 98 software package with different basis sets. The results are compared with the dependences obtainedby the semiempirical methods. The basic relationships of the R-centroid method are derived, and the quasi-classical nature of this method is demonstrated. It is confirmed that the dependence of the electronic transition dipole moment on the internuclear separation is described most reliably by using the semiempirical methods. The vibronic transition dipole moment is shown to be an oscillating function of the vibrational quantum number v1 (with v2=const) or v2 (with v1=const).     

Transition moments and NH2 cometary spectra

We calculate vibronic transition moments for the A^?2A_1-X^?2, electronic band system, and for the vibrational transitions within the à and [Xtilde] states, of the NH₂ free radical with the purpose of assisting in the quantitative interpretation of cometary NH₂ emission spectra. To do this it is necessary to use molecular wavefunctions, and electric dipole moment and transition moment surfaces. The wavefunctions are obtained using our program system RENNER after we have determined optimized à and [Xtilde] state potential energy surfaces in a fitting to data. We have obtained the electric dipole moment and transition moment surfaces by ab initio calculation.     

Infrared spectrum of stannous oxide (SnO)

A tunable diode laser has been used to measure the infrared spectrum of stannous oxide (SnO) in the gas phase between 830 and 868 cm^?1. Measurements of the v = 1-0, 2-1, 3-2, and 4-3 transitions have been made at temperatures ranging from 930 to 1150°C. Over 175 infrared transitions of the nine most abundant SnO isotopic species have been combined with microwave measurements reported by others in a single least-squares analysis of the data to yield a set of eight Dunham coefficients for the X¹Σ⁺ state of SnO. The data have also been fit by a nonlinear least-squares procedure to obtain B_e, ω_e, and the first five Dunham potential constants. The band center for the vibrational transition of ¹²⁰Sn¹⁶O is found at ν₀ (v = 1?0) = 814.70249 ± 0.00027 cm^?1.     

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.     

Laser Stark spectroscopy; a case study in the ν2 fundamental band of 14NH3

The ν₂ fundamental band of ¹⁴NH₃ 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_3v molecule is presented on the basis of the conventional theory of vibration-rotation.     

l-type doubling transitions in Δ states of OCS

Molecular beam electric resonance spectroscopy has been used to measure the l-type doubling transitions in carbonyl sulfide. Transitions in J = 4 to J = 20 have been observed for the (02²0) vibrational state and for J = 1 and J = 2 for the (03¹0) state. The data has been analyzed to give the v = 2 energy separation $\text{E}{}_{\mathrm{<mtext>\Delta </mtext>}}{}^0\text{- E}{}_{\mathrm{<mtext>\Sigma </mtext>}}{}^0\text{= ?5.7861(2) + 8.36(1) × 10}{}^{\mathrm{?5}}\text{J(J + 1)}\text{cm}{}^{\mathrm{?1}}$, and the vibrational dependence of q to be 86.52(9)(v₂ + 1) KHz. The dipole moment of the (02²0) vibrational state is 0.6936(3) D.     

Resonant fluorescence of gaseous bromine excited by the 5145 Å radiation of a single longitudinal mode argon ion laser

The resonant fluorescent spectra of gaseous bromine excited by the single longitudinal mode 5145 Å radiation of an argon ion laser were reinvestigated. Three new transitions were found in addition to the five previously reported. The excitation frequency and the fluorescent line positions from Δv = 1 to Δv = 9 were carefully measured for each of the eight transitions. The fluorescent lines of Δv = 5 and Δv = 10 are too weak to be detected. The isotopic molecules and the vibration-rotation states involved were assigned. All the fluorescent line positions up to Δv = 10 were calculated, and they agreed with the observed values to within 0.2 cm^?1. The relative intensities in each progression also agreed with the known Franck-Condon factors.