Rotation-vibration-translation energy transfer in laser excited Li2 (B1Πu)

Using the method of laser fluorescence, inelastic collisions with rare gas atoms of electronically excited ⁷Li₂ molecules in the υ = 2 and 4 levels were studied. Vibrational transitions ranging from Δ = +2 to ?4 were observed. The simultaneous rotational transitions were completely resolved, and detailed rate constants k_{Δυ, ΔJ} for specific collision- induced quantum jumps Δυ, ΔJ were determined. The effect of secondary rotational relaxation was eliminated by an extrapolation to zero pressure. By integration over ΔJ, rate constants k_Δυ, were found. They are, within the error limits, independent of the collision partner and on the initial υ (2 or 4) and depend rather weakly on Δυ. These findings are compared with theoretical results from various methods, generally based on a collinear collision model. The apparent disagreement in all respects suggests strongly the importance of rotational degrees of freedom in the collision. Experimental evidence for this is the large amount of V — R transfer observed, which about equals the V — T transfer. The mean cross sections σ(Δυ) for specific vibrational transitions Δυ range between 6 and 15 A², among the largest ever observed.     

First-order stark effect and electric dipole moment of H3P … HC15N by pulsed-nozzle fourier-transform microwave spectroscopy

The first-order Stark effect in the J = 4 ← 3, K = 1 transition of the weakly bound dimer H₃P … HC¹⁵ N has been obeserved and measured by pulsed-nozzle Fourier-transform microwave spectroscopy under the selection rules ΔM = O and ΔM = ± 1. The electric dipole moment μ= 4.046(47) D determined for H₃P … HC¹⁵ N has been interpreted in terms of an enhancement Δμ = 0.60 D on dimer formation.     

Hyperfine and Stark spectrum of DBr in the millimeter-wave region

The hyperfine and Stark spectrum of the J = 1←0 rotational transition of D⁷⁹Br and D⁸¹Br at 254 CHz has been investigated with a high resolution millimeter-wave beam-spectrometer. The hyperfine coupling constants and the dipole moment of D⁷⁹Br and D⁸¹Br have been determined. A discussion is given on the values of the field gradient and the dipole moment at the equilibrium intermuclear distance of the hydrogen bromide molecule.     

Stark effect,polarizabilities and the electric dipole moment of heteronuclear diatomic molecules in 1Σ states

The theory of second-order Stark effect in ¹Σ states of heteronuclear diatomic molecules is thoroughly reviewed. The rigorous treatment given demonstrates that by introducing rotational, vibrational and electronic branch polarizabilities, the intrinsic character of the second-order Stark effect in diatomic molecules can be shown to be related more closely to polarizabilities than to dipole moments. The well-known expression for the Stark shift in ¹Σ levels which is dominated by the square of the dipole moment is only a crude, though sufficient approximation whenever large dipole moments are involved. For small dipole moments, however, this approximation is likely to fail, leading to an erroneous determination of such dipole moments. In the limiting case of negligible influence of the molecular rotation on the vibronic matrix elements, the arithmetic mean of the electronic branch polarizabilities turns out to be equal to the well-known static electronic polarizabilities α_∥ and α_⊥. The results are applied to the interpretation of the Stark splitting in the A¹Σ⁺, υ′ = 5, J′ = 1 level of ⁷LiH, recently determined by Stark quantum-beat spectroscopy.     

D-nuclear quadrupole coupling in the rotational spectrum of 15N2…DF and an interpretation of the hyperfine coupling constants χ aaD and DaaHF within a series of complexes B…HF

Hyperfine structure in the J = 1 ← 0 and J = 2 ← 1 transitions of ¹⁵N₂…DF, arising from D-nuclear quadrupole coupling and D, ¹⁹F nuclear-spin—nuclear-spin coupling, has been observed and measured by using pulsed-nozzle Fourier-transform microwave spectroscopy. The following rotational, centrifugal distortion and hyperfine coupling constants were determined: β_o = 3091.9004 MHz, D_J = 14.75 kHz, χ_aa^D = 278.6(38) kHz and D_aa^HF = ?38.5(38) kHz. An interpretation is presented for the variation of the coupling, constants χ_aa^D and D_aa^HF along the series B…DF and B…HF, where B = Ar, Kr, Xe, ¹⁵N₂, CO, PH₃, H₂S, HC¹⁵N and H₂O.     

Electric dipole moment of BrCl

The electric dipole moment of the BrCl molecule has been determined by a study of the Stark effect on nine hyperfine components of the J = 1 ← 0 rotational transition lying at 9 GHz. A direct diagonalisation procedure of the energy matrix of the total hamiltonian has been used and the electric dipole moment derived for the ground vibrational state of BrCl is |μ_o| = 0.519 ± 0.004 D.     

Microwave spectrum,centrifugal distortion constants,dipole moment and quadrupole coupling constants of pentafluoropyridine

Pentafluoropyridine has been analysed in the frequency range of 8 to 18 GHz at dry ice temperature, using a conventional 100 kHz Stark modulated microwave spectrometer. The rotational constants and centrifugal distortion constants are A = 1481.539 ± 0.003 MHz, B = 1075.348 ± 0.004 MHz and C = 623.101 ± 0.001 MHz; and d_J = ?0.39 ± 0.06 kHz, d_JK = 1.86 ± 0.27 kHz, d_K = 0.70 ± 0.1 kHz, d_EJ = (0.3 ± 0.03) × 10^?6 and d_EK = (?1.5 ± 0.2) × 10^?6. The electric dipole moment has been found to be 0.98 ± 0.08 D and the values of the quadrupole coupling constants are x_aa = 1.94 ± 0.22 MHz, x_bb = ?4.08 ± 0.06 MHz and x_cc = 2.14 ± 0.22 MHz. A simple analysis based on Townes and Dailey theory points to a considerable increase in the π-electron density and excess charge on the nitrogen site.     

Microwave spectrum,dipole moment and AB initio structure of iminopyruvonitrile (CH3C(CN)NH)

The microwave spectrum of iminopyruvonitrile has been investigated from 19 to 51 GHz. Rotational transitions have been assigned for the vibrational ground state and the rotational and centrifugal distortion constants have been adjusted. The electric dipole components μ_a = 1.806(6), μ_b = 0.759(21) and μ_total = 1.958(10) D have been deduced from Stark splittings. Some rotational transitions showed splittings arising from the internal rotation of the methyl group, the barrier to which has been determined to be V₃ = 593.5(89) cm⁻¹. Different conformations have been predicted via ab initio calculations and are compared to the microwave results.     

Raman spectroscopy of the [TeX6]2− ions (X  Cl or Br) at resonance with their lowest 3T1u and 1T1u states: Evidence for tetragonal distortion in these excited states

The observation that the v₂(e_g) band is the most enchanced Raman band at resonance with the bands assigned to both the ³T_1u ← ¹A_1g and ¹T_1u ← ¹A_1g transitions of the [TeX₆]^2? ions indicates that the ions are tetragonally distorted in these excited states. The depolarisation ratio of 2v₂ band of [TeBr₆]^2? at resonance with the ¹T_1u ← ¹A_1g transition is found to be 0.18, in close agreement with that expected (3/14) for the first overtone of a doubly degenerate vibration coupled to a triply degenerate excite state.     

Microwave-optical double resonance in molecular ions. Co+

Microwave—optical double resonance signals have been detected in a mass-selected ion-beam spectrometer for ¹²C¹⁶O⁺. With the optical excitation of fluorescence from the R₁ ($\text{1}\text{2}$) line of the (0,0) band of the A²Π_{$\text{3}\text{2}$} ← X²∑ transition of 20350.6 cm^?1, the microwave resonances occurred at 118101.8 ± 0.2 MHz and at 117694 ± 2 MHz corresponding to the N= 1, J = $\text{3}\text{2}$ ← N = 0, J = $\text{1}\text{2}$ and the N = 1, J = $\text{1}\text{2}$ ← N = 0, J = $\text{1}\text{2}$ transitions.     

Microwave spectrum,dipole moment and barrier to internal rotation of trans-methyl glyoxal

The microwave spectrum of the trans conformer of methyl glyoxal has been investigated in the frequency range from 8 to 40 GHz. The rotational constants have been determined for the A state: A = 9102.4332(31), B = 4439.8832(27) and C = 3038.9404(22) MHz. Quantitative measurements of the Stark effect have yielded the components of the electric dipole moment: μ_a = 0.1597(11), μ_b = 0.9620(7) and μ_total = 0.9751(7) D. From the splittings of rotational transitions the three-fold barrier to internal rotation of the methyl top has been found to be V₃ = 269.1 (3) cm^?1.     

Molecular zeeman effect in NH3

High-resolution measurements of ΔM_j = 0 inversion transitions in ¹⁴NH₃ in 100 kG magnetic fields were made using a beam-maser spectrometer. The spectra show resolved splittings due to a different in molecular g-values for upper and lower inversion states with J = 3, K = 2. The observed difference in upper and lower inversion state g-values is g⁺(3,2)—g^?(3,2) = (1.38 ± 0.08) > 62;x 10^?4.     

Hyperfine structure of SrCl X2∑+ by microwave—optical polarization spectroscopy

The hyperfine structure of the X²∑⁺, υ = 0 state of ⁸⁸Sr³⁵Cl has been investigated using microwave—optical polarization spectroscopy. Resolution of the hyperfine structure in transitions between low-lying rotational states has allowed the first determination of magnetic dipole and electric quadrupole coupling constants. The results are: b = 18.663(89) MHz, c = 7.72(30)MHz, and eqQ = 3.96(84) MHz.     

Microwave spectrum of N2D4, 14N quadrupole coupling constants,and the barrier to inversion of the amino group

The microwave spectrum of N₂D₄ has been observed and analyzed. Based on five low-J rotational transitions the effective rotational constants are: A = 74712.9 ± 1.9 MHz, B = 18500.42 ± 0.46 MHz, and C = 18439.91 ± 0.46 MHz. The quadrupole coupling constants of the ¹⁴N nuclei are X_aa = 4.23 ± 0.04 MHz, X_bb = 1.98 ± 0.05 MHz, and X_cc = ?2.25 ± 0.05 MHz. Using the observed ground state inversion splittings for N₂D₄ and N₂H₄ the barrier to inversion of a single amino group is computed to be 5.00 kcal mol^?1.     

The 6Liz A1Σu+ ∼ b3Πu spin—orbit perturbations: Sub-Doppler spectra and steady state kinetic lineshape model

The ⁶Li₂ A¹Σ_u⁺ υ_A = 2, J = 33 and υ_A = 9, J = 20 levels are shown to be spin—orbit perturbed by the b³Π_u υ_b = 9, F₁e N = 32 and υ_b = 15, F₁e N = 19 levels from which an electronic matrix element of <b³Π_oc|H^SO|A¹Σ⁺ > = 0.114±0.006 cm^?1 is determined. Previous estimates of this quantity are shown to be incorrect. Although the main and extra levels are separated by less than the 900 K Doppler width of A¹Σ_u⁺ ? X¹Σ_g⁺ rotational lines, sub-Doppler intermodulated fluorescence and perturbation-facilitated optical—optical double resonance spectra allow direct observation of the separation of main and extra levels. The mixing coefficients and other perturbation parameters are inferred from a steady state kinetic model of the composite main plus extra lineshape.     

Collision rotational transfers in NaH A1Σ+ by He,Ar or H2 (and in KH A1Σ+ by H2)

The total and relative rotational transfer cross sections σ_total and σ_Ji-Jf, by collisions of NaH A¹Σ with He, Ar or H₂, are measured from υ′ = 4 and υ′ = 11, J₁′ = 6. The σ_total increase as υ′ increases. They are similar for He and H₂ but much greater for Ar especially at large υ′. In NaH A¹Σ⁺ the bond goes from covalent to ionic as υ′ increases: σ_total is very sensitive to an attractive potential due to the interaction of the permanent electric dipole moment of the molecule with the polarizability of the atom (α_Ar = 11 au, α_He = 1.37 au). The σ_Ji-Jf decrease monotonously as |J_f-J_i| increases and may be fitted by a scaling law. The variation with ΔJ depends on the colliding gas but does not change appreciably with υ′: most of the transfers could take place on the repulsive part of the interaction potential, the shape of which would not depend on υ′.     

Microwave spectrum and dipole moment of glycolic acid

More than 200 rotational transitions of glycolic acid (CH₂OHCOOH) have been assigned in the frequency range 18–40 GHz. Rotational constants and centrifugal distortion constants for the ground state and two vibrationally excited states were deduced. From Stark splittings the dipole moment was determined: μ_a = 1.913(5), μ_b = 0.995(14) and μ_total = 2.156(9) D.     

Sub-doppler two-photon spectrum of asymmetric rotor molecules: analysis of the qqQ rotational branch of the S1(1B2u)141 ← S0(1A1g) system of benzene-d1

The Doppler-free two-photon excitation spectrum of the ^qqQ branch of the 14¹₀ vibrational band of the S₁(¹B_2u) ← S₀(₁A_1g) transition of benzene-d₁ has been recorded using a cw single-mode dye laser coupled to an external concentric resonator. The spectrum has been analysed using a non-rigid Watson Hamiltonian. More than 200 lines with J up to 20 have been assigned and the rotational constants which best reproduce the spectrum are A¹_v = 0.181435, B¹_v = 0.169990, C¹_v = 0.089055 cm⁻¹. The K_a = odd lines of the ^qqQ₅(J) subbranch show small and quite regular perturbations of 60 ± 5 MHz which are probably due to a coupling to another vibrational state of the S₁ manifold.     

Stark modulation in the ã A2—X̃,Σg system of CS2

Stark modulation experiments have been carried out on bands of the ã ³A₂—X̃,¹Σ_g⁺ system of ¹²C³²S₂. The most pronounced effects involve nearly degenerate pairs of rotational levels ofthe type J_o,j and J−1_1,J−1 with odd values of J in the 040, 140, 050, 060, 070 and 080 vibrational levels of the upper state. A further effect has been observed in the 090 level but the mechanism has not yet been clarified. Dipole moments have been determined for all vibrational levels except the 080 and 090 which are perturbed. A marked vibrational dependence of the dipole moment is found. ‡|Taken in part from the thesis of M. Larzillière, Doctorat d'Etat, ref : Serie A.O. No. 12772, 1977 Reims, France. †|Laboratoire de Spectrométrie Ionique et Moléculaire, Universités de Lyon I et de St-Etienne, associé au C.N.R.S.     

The Fourier transform and diode laser spectrum of the ν2 band of diazomethane

The infrared spectrum of the ν₂ band (NN stretching) of gaseous diazomethane at 2100 cm^?1 has been measured by means of an interferometer and a tunable diode laser spectrometer. For the first time the rotational J and K_a structure of this A-type parallel band has been resolved. Since the spectrum was found to be perturbed it was not possible to fit the upper state levels to an overall hamiltonian. Nine subbands have been analysed with the support of millimeter wave data for the ground vibrational state. Term values for the ν₂ = 1 vibrational state with K_a up to 5 have been obtained and subband origins, effective rotational constants B and centrifugal distortion constants D and H were determined for each K_a substate.