Infrared-infrared Double Resonance Research Articles

Analysis of the hyperfine structure of the Cs2[formula omitted] state

We report on theoretical calculations and analyses of the hyperfine structures in the spectra of the Cs233Σg+ state observed by Li et al by infrared-infrared (IR-IR) double resonance spectroscopy in 2008. For this purpose, we consider the excitation–de-excitation schemes in their entirety, taking into account the mixed character of the intermediate levels of the A1Σu+∼b3ΠΩu system, which generally contains contributions from all Ω=0,1,2 basis states. We also avoid an approximation for the strongest features in the spectra (the major component), in which the probabilities of optical dipole transitions are computed from 0-th order state vectors alone. We compute the contributions from all components of the mixed states. The fundamental theory and algorithms are described, the parameters of the chosen model are fitted and reported, and the results of the simulation are presented.

Cryogenic Ion Spectroscopy for Identification of Monosaccharide Anomers.

We combine conformer-selective, cryogenic infrared spectroscopy, quantum mechanical computations, and 18O substitution at the reducing end to determine the structural preferences of protonated glucosamine in the gas phase. Cryogenic infrared-infrared (IR-IR) double resonance spectroscopy of helium-tagged, protonated glucosamine provides vibrational fingerprints of individual conformers, and 18O isotopic labeling facilitates the match with computed structures and provides a selective probe of the anomeric hydroxyl. This is key for using vibrational spectroscopy for glycan analysis and determining the generality of anomeric memory during glycosidic bond cleavage.

Experimental study of the [formula omitted] and [formula omitted] states of [formula omitted

Twelve ro-vibrational energy levels of the 85Rb2b3Π1u state have been observed using the Perturbation Facilitated Infrared-Infrared Double Resonance (PFIIDR) technique for the first time.Using the new observed levels as intermediate window levels, dozens of transitions into the 85Rb223Π1g upper state ro-vibrational levels have been recorded.Compared with the experimental data of the 85Rb223Π0g state, the average term value difference between the observed Ω=1 and Ω=0 components of the 85Rb223Πg state levels with the same rotational quantum number, is approximately 83.1±0.3cm-1. This proves that the 23Πg state has a spin-orbit splitting of 83.1±0.3cm-1, which shows that the 23Πg state tends to belong to Hund’s case (a).

Observation of the [formula omitted] State of [formula omitted

Using Infrared-Infrared Double Resonance (IIDR) high resolution spectroscopy, we have observed the 20200–21600cm−1 energy range of the 41Σg+ electronic state of Rb2. The absolute vibrational quantum number assignment is based on the isotope effect using 824 rovibrational levels assigned to the 85Rb85Rb and 85Rb87Rb isotopomers. In addition to perturbations between the 41Σg+ and 31Σg+ state, strong couplings between the 41Σg+ and 23Πg states were observed. Preliminary molecular constants and an RKR potential energy curve are given.

Updated potential energy function of the Rb2 $a^3\Sigma _u^+$a3Σu+ state in the attractive and repulsive regions determined from its joint analysis with the 23Πg state

We report new experimental data for the Rb2 a(3)Σu(+) and 2(3)Π0g states obtained using the Perturbation Facilitated Infrared-Infrared Double Resonance (PFIIDR) technique. The results include ro-vibrational term values of the 2(3)Π0g state and resolved fluorescence spectra of the 2(3)Π0g→a(3)Σu(+) transitions for a wide range of rotational and vibrational quantum numbers. An analysis of these data confirms the initial assignment of the transitions to the a(3)Σu(+) state reported in our earlier work [B. Beser, V. B. Sovkov, J. Bai, E. H. Ahmed, C. C. Tsai, F. Xie, L. Li, V. S. Ivanov, and A. M. Lyyra, J. Chem. Phys. 131, 094505 (2009)]. The potential energy functions of the Rb2 a(3)Σu(+) and 2(3)Π0g states are derived from a simultaneous fit of the available experimental data. The improved potential function of the Rb2 a(3)Σu(+) state spans both the attractive and repulsive regions starting with internuclear distance R ∼ 4.5 Å.

Collisional Line Assignments and Hyperfine Structure Interpretation in Cs2 23Δ1g State

Accurately known energy level structure of the Cs2 A1Σu+−b3Πu complex of states from a recent global de-perturbation of these states has enabled additional assignments of 140 perturbation facilitated infrared-infrared double resonance (PFIIDR) transitions to the 23Δ1g state from collisionally populated intermediate A1Σu+ levels. Together with the 221 previously observed 23Δ1g←A1Σu+←X1Σg+ double resonance lines [J. Chem. Phys. 128, 204313 (2008)], molecular constants and the Rydberg-Klein-Rees potential energy curve of the 23Δ1g state have been recalculated (excluding 54 perturbed levels). The centrifugal distortion constant has been determined and agrees well with the value calculated based on standard empirical formulas. The hyperfine structure of the 23Δg state, which has not resolved in our sub-Doppler excitation spectra of the 23Δ1g state, has been interpreted with a preliminary simulation.

ChemInform Abstract: Observation of Dynamic Stark Splitting in Infrared-Infrared Double Resonance in Methyl Fluoride.

Abstract Dynamic Stark splitting has been observed by scanning the Q P (5, 3) transition in the 2 ν 3 - ν 3 band in 13 CH 3 F with a CO 2 -laser based infrared microwave sideband generator while pumping the Q R (4, 3) transition in the ν 3 band with a second CO 2 laser. Similar splitting has been observed in the Q Q (12, 9) and Q R (12, 9) transitions in the 2 ν 3 - ν 3 band of 12 CH 3 F while pumping the Q R (11, 9) transition in the ν 3 band. The lineshapes of these and other double resonance effects have been fit to high accuracy by means of a computer program that computes the spectrum by solving the density matrix equations for a three-level system including summation over the spatially degenerate states and numerical integration over the velocity. The effects of contributions from collisional energy transfer, frequency modulation of the lasers, and misalignment of the laser beams have been calculated and are discussed. Difficulties that must be overcome in order to use these experiments for determination of energy transfer rates are described.

Experimental investigation of the R85b2 a Σ3u+ triplet ground state: Multiparameter Morse long range potential analysis

Using perturbation facilitated infrared-infrared double resonance excitation of the (85)Rb(2) molecule, we have observed spectrally resolved fluorescence to the a (3)Sigma(u)(+) state. We have analyzed the rovibrational energy level structure of the (85)Rb(2) a (3)Sigma(u)(+) state and derived a multiparameter Morse Long Range (MLR) potential and molecular constants for this state, which can be used to predict term values without needing to solve the radial Schrödinger equation.

Experimental investigation of the Cs2 a Σ3u+ triplet ground state: Multiparameter Morse long range potential analysis and molecular constants

We have observed the vibrational levels v(") = 0-40 of the Cs(2) a (3)Sigma(u)(+) state by perturbation facilitated infrared-infrared double resonance excitation and spectrally resolved fluorescence measurements, and derived a multiparameter Morse long range potential and molecular constants based on these data.

Observation and calculation of the Cs2 2Δ1g3 and bΠu3 states

The Cs2 2Δ1g3 and bΠ0u3 states have been observed by infrared-infrared double resonance spectroscopy for the first time. 221 2Δ1g3←AΣu+1←XΣg+1 double resonance lines have been assigned to transitions into the 2Δ1g3 v=6–13 vibrational levels. Resolved fluorescence into the bΠ0u3 v′=0–48 levels has been recorded. Molecular constants and potential energy curves are determined by the global fit of the entire set of the experimental data. Theoretical potential energy curves of the 2Δg3 and bΠu3 states have been determined in the framework of the pseudopotential method and are compared with the experimental results.

The K239 2Σg+3 state: Observation and analysis

The K239 2Σg+3 state has been observed by perturbation-facilitated infrared-infrared double resonance spectroscopy and two-photon excitation. Resolved fluorescence spectra into the aΣu+3 state have been recorded. The observed vibrational levels have been assigned as the v=23–25, 27, 28, 31–33, 38–45, 47, and 53 levels by comparing the observed and calculated spectra of the 2Σg+3→aΣu+3 transitions. Molecular constants have been obtained using a global fitting procedure with a comprehensive set of experimental data. Fine and hyperfine splittings have been resolved in the excitation spectra. Perturbations between the 2Σg+3 and 2Πg3 states were observed. The hyperfine patterns of the 2Σg+3 levels are strongly affected by the perturbation. The perturbation-free and weakly perturbed levels follow the case bβS coupling scheme, while the perturbed levels follow case bβJ coupling. A Fermi contact constant, bF=65±10MHz, has been obtained. Intensity anomalies of rotational lines appeared both in the 2Σg+3∼2Πg3←bΠu3 excitation spectra and in the 2Σg+3∼2Πg3→aΣu+3 resolved fluorescence spectra. These intensity anomalies can be explained in terms of a quantum-mechanical interference effect.

The K2 23Πg State: New Observations and Analysis

Totally 3045 transitions into the 2(3)Pi(g) v = 0-42, J = 0-103, Omega = 0, 1, 2 rovibrational levels have been observed by infrared-infrared double resonance fluorescence excitation and two-photon spectroscopy. Molecular constants including the spin-orbit interaction parameters are obtained. Although the K2 2(3)Pi(g) state dissociates to the 4s + 3d atomic limit, it is strongly mixed with the 3P ionic states in the range of the potential well. This mixing results in a relatively large equilibrium internuclear distance Re = 5.254 A and a larger spin-orbit constant A0 approximately 14.17 cm(-1) than that of the atomic limit -2.33 cm(-1). Strong perturbations of the 2(3)Pi(g) levels observed are attributed to the spin-orbit coupling with the 4(1)Sigma(g)+ state.

Experimental study of the K2392Πg3 state by perturbation facilitated infrared-infrared double resonance and two-photon excitation spectroscopy

The 39K2 2 3Pi(g) state has been observed by perturbation facilitated infrared-infrared double resonance and two-photon excitations. The vibrational numbering of the 2 3Pi(g) levels was determined by resolved fluorescence into the bound levels as well as to the continuum of the a 3Sigma(u)+ state. The rotational assignment of the 2 3Pi(g) levels excited by two-photon transitions was determined from excitation frequencies and resolved fluorescence into the bound levels of the a 3Sigma(u) + and b 3Pi(u) states. Molecular constants obtained from these observed levels agree with theoretical constants.

Infrared-infrared double resonance spectroscopy of cyanoacetylene in helium nanodroplets.

Infrared-infrared double resonance spectroscopy is used as a probe of the vibrational dynamics of cyanoacetylene in helium droplets. The nu1 C-H stretching vibration of cyanoacetylene is excited by an infrared laser and subsequent vibrational relaxation results in the evaporation of approximately 660 helium atoms from the droplet. A second probe laser is then used to excite the same C-H stretching vibration downstream of the pump, corresponding to a time delay of approximately 175 micros. The hole burned by the pump laser is narrower than the single resonance spectrum, owing to the fact that the latter is inhomogeneously broadened by the droplet size distribution. The line width of the hole is characteristic of another broadening source that depends strongly on droplet size.

Infrared-infrared double resonance spectroscopy of Ar-HF. Intermolecular state dependence of the dipole moment and vibrational predissociation in vHF = 2

Stark spectra have been measured for Ar-HF in several intermolecular bending and stretching states associated with v HF = 1. The resulting dipole moments are compared with those calculated using the most recent potential energy surface. Infrared-infrared double resonance spectroscopy is used to access the corresponding states in v HF = 2 where, in the absence of intermolecular excitation, dissociation occurs before the molecules can reach the detector. Simultaneous excitation of the Σ or Π bending vibrations, which have the effect of making the hydrogen atom point away from argon atom on average, results in lifetimes in excess of the molecular flight time (0.3 ms).

Transfer of rotational population in NH3by infrared-infrared double resonance

In this paper we report experimental and theoretical results on total inelastic cross-sections for NH3 molecules colliding with H2 at room temperature. The use of time resolved infrared-infrared double resonance allows one to follow the population relaxation for different energy levels of NH3. A CO2 pulsed pump laser tuned to a line in the v 2 band of NH3 induces a transient transfer of population and the return to equilibrium is probed with a c.w. diode laser turned to lines in the v 4 band of NH3. The time evolution of the probe absorption for different pressures of the two gases is then related to the inelastic cross-sections of the states involved. The so-determined cross-sections for the (j = 5, k = 4, e = +1) and (j = 1, k = 1, e = -1) states of NH3 are respectively 27 A2 and 31 A2. We have also calculated inelastic cross-sections using a semi-classical model and an ab initio potential energy surface for different values of (j, k, e) (i.e. j = 1, 2, 3, k = 1, 2, 3 and e = ±1) and of j 2 (total angul...

Infrared-infrared double resonance study of methyl alcohol

In this work we carried out an infrared-infrared (IR-IR) double resonance (DR) study of methyl alcohol using a CO 2 laser and a lead salt diode laser, in order to confirm previously proposed far-infrared (FIR) laser assignments for the 9P(34) and 9P(16) CO 2 laser lines. For the 9P(34) CO 2 laser line it is confirmed that the pump radiation excites the torsionally excited Q(125, 9) transition of methyl alcohol in agreement with the assignments proposed earlier. From the study it was noticed that due to the pump radiation, transitions which are not connected by dipole selection rules either to the lower or upper pumped level were also affected. Thus it appears that four-level IR-IR DR experiments are unlikely to provide useful information for transition assignments. The diode laser study was coupled with a recent spectroscopic study using a high resolution Fourier transform spectrometer to detect and identify hot band and perturbation allowed transitions in CH 3OH.

Infrared-infrared double resonance of methyl fluoride in foreign gases

Infrared-infrared double-resonance spectra have been recorded for samples of methyl fluoride gas in an excess of hydrogen, helium, argon, and xenon, as well as for mixtures of 12CH 3F and 13CH 3F. The double-resonance effects appear as a narrow transferred spike superimposed on a broad Gaussian lineshape of the expected Doppler width. When the foreign gas has a dipole moment or is a relatively light perturber, the spike dominates the lineshape, but when the foreign gas is a relatively heavy atom, the Gaussian dominates. The spectra for all of the samples show evidence of a Δ k = 3 n ( n = an integer or zero) selection rule for collisionally induced rotational transitions. The spectra with argon and xenon as foreign gas demonstrate that collisions with these atoms can induce direct vibration-rotation energy changes from v 3 = 1 to v 6 = 1 in methyl fluoride and that the selection rule for these transitions is Δ( k − l) = 3 n. The double-resonance spectra with argon and xenon as a foreign gas also show a frequency shift that is substantially larger than the shift for single-resonance spectra in the same mixture. One-dimensional collision kernels have been calculated by classical mechanics and appear to display most of the characteristics of the experimental spectra.

New infrared-infrared double resonance spectra of CH 3OH

Several new Stark tuned infrared-infrared double resonance spectra have been observed when the CH 3OH molecule was investigated using an acousto-optic modulated single-mode cw CO 2 laser. The observations have confirmed the assignments of three previously reported infrared absorption transitions. New assignments have been proposed for three transitions while partial assignments have been obtained for three transitions and a previously observed double resonance has been reassigned. The results have allowed the determination of the permanent electric dipole moment components μ″ a and μ′ a for several ground state and CO stretch state levels including excited torsional state levels. Assignments of optically pumped far-infrared laser lines associated with two of the infrared transitions are proposed.

Observation of dynamic Stark splitting in infrared-infrared double resonance in methyl fluoride

Dynamic Stark splitting has been observed by scanning the Q P(5, 3) transition in the 2 ν 3- ν 3 band in 13CH 3F with a CO 2-laser based infrared microwave sideband generator while pumping the Q R(4, 3) transition in the ν 3 band with a second CO 2 laser. Similar splitting has been observed in the Q Q(12, 9) and Q R(12, 9) transitions in the 2 ν 3- ν 3 band of 12CH 3F while pumping the Q R(11, 9) transition in the ν 3 band. The lineshapes of these and other double resonance effects have been fit to high accuracy by means of a computer program that computes the spectrum by solving the density matrix equations for a three-level system including summation over the spatially degenerate states and numerical integration over the velocity. The effects of contributions from collisional energy transfer, frequency modulation of the lasers, and misalignment of the laser beams have been calculated and are discussed. Difficulties that must be overcome in order to use these experiments for determination of energy transfer rates are described.