Laser Supersonic Jet Research Articles

Combined synchrotron-based high resolution FTIR and IR-diode laser supersonic jet spectroscopy of the chiral molecule CDBrClF

The rovibrational spectrum of Deuterobromochlorofluoromethane CDBrClF has been measured with a resolution of better than 0.001cm−1 at room temperature with the Zurich Bruker IFS spectrometer prototype (ZP 2001) using a globar source, and with the Bruker prototype 2009 interferometer connected to the Swiss Light Source (SLS) synchrotron as a radiation source providing a resolution of 0.0007cm−1 in the range 600–1100cm−1. In addition CDBrClF has been measured at low rotational temperature (Trot=15K) with our diode laser supersonic jet setup around 748cm−1 in the ν5 region (resolution 0.0013cm−1). The spectra of the two major isotopomers CD79Br35ClF and CD81Br35ClF have been analyzed within the ν5 (CCl-stretch, ν̃0=748.2998cm−1 (CD79Br35ClF), ν̃0=748.1541cm−1 (CD81Br35ClF)), ν4 (CF-stretch, ν̃0=1082.8116cm−1 (CD79Br35ClF), ν̃0=1082.7963cm−1 (CD81Br35ClF)) and ν3 (DCF-bend, ν̃0=918.3715cm−1 (CD79Br35ClF), ν̃0=918.0206cm−1 (CD81Br35ClF)) regions. A detailed rovibrational analysis of these bands is presented. A combined analysis of the ν3,ν4 and ν5 fundamental bands provides accurate rotational and quartic centrifugal distortion constants for the vibrational ground state and for the states ν3,ν4 and ν5 of CD79Br35ClF and CD81Br35ClF. The results are discussed in relation to intramolecular (ro)vibrational redistribution (IVR) and also possible experiments pertaining to the experimental detection of molecular parity violation.

Gas phase ultraviolet and infrared spectroscopy on a partial peptide of β2-adrenoceptor SIVSF-NH2 by a laser desorption supersonic jet technique.

Laser desorption supersonic jet laser spectroscopy has been applied to a penta-peptide, Ser-Ile-Val-Ser-Phe-NH2 (SIVSF-NH2), which is a partial sequence of a binding site in a β2-adrenaline receptor protein. By comparing the resonance enhanced multiphoton ionization spectrum with the ultraviolet-ultraviolet hole burning (HB) spectrum, it is concluded that only a single conformer exists. The infrared (IR) spectrum of the X-H stretching region, measured by IR dip spectroscopy, shows that all of the OH and NH groups form hydrogen bonds. The structure of SIVSF-NH2 is assigned by the combination of a force field calculation (CONFLEX) and quantum chemical calculations both in S0 and S1. Over 20 000 stable conformations, given by CONFLEX, are classified into 6987 groups and 1068 groups in which all of the NH and OH bonds are hydrogen-bonded are selected. The most stable structure in each group was geometrically optimized by density functional theory (DFT) calculations, and theoretical IR spectra were calculated for the conformers for which the energies are within 10 kJ mol(-1) of the most stable one. It has been found that the most stable and the secondmost stable conformers well-reproduce the observed IR spectrum. The vibrational frequencies in S1 were also calculated for these two conformers. According to the reproduction of the vibrational frequencies in the HB spectrum, the structure of SIVSF-NH2 is assigned to the most stable conformer, which forms a hydrogen-bonded structure corresponding to a compact, distorted version of the beta hairpin of peptides and proteins.

Revised conformational assignments and conformational evolution of tyrosine by laser desorption supersonic jet laser spectroscopy

The number of conformers and their structures of tyrosine are reassigned on the basis of resonance enhanced multiphoton ionization (REMPI), ultraviolet-ultraviolet hole burning (UV-UV HB), infrared (IR) dip spectra, and quantum chemical calculations. From comparison between REMPI and UV-UV HB spectra, it was found that 12 conformers coexist in the supersonic jet. The structures of these conformers are determined by the IR spectra and theoretical calculations. The number of conformers is more than that reported in the previous reports (8 conformers), and is rationalized by the systematic formation of conformers from simpler molecules without substituents, just like evolution. The importance of dipole-dipole interaction between an amino-acid chain and hydroxyl group at the benzene ring was also discussed.

Conformational reduction of DOPA in the gas phase studied by laser desorption supersonic jet laser spectroscopy

The conformational reduction in catecholamine neurotransmitters was studied by resonance enhanced multi photon ionization (REMPI), ultraviolet-ultraviolet (UV-UV) hole burning and infrared (IR) dip spectroscopy with applying a laser desorption supersonic jet technique to DOPA, which is one of the catecholamine neurotransmitters and has one more phenolic OH group than tyrosine. It is concluded that DOPA has a single observable conformer in the gas phase at low temperature. Quantum chemical calculations at several levels with or without the dispersion correction were also carried out to study stable conformations. From the comparison between the computational IR spectra and the experimental ones, the most stable structure was determined. It is strongly suggested that the conformational reduction is caused by electrostatic interactions, such as a dipole-dipole interaction, between the chain and OH groups.

Direct observation of the symmetric stretching modes of à 1 A u acetylene by pulsed supersonic jet laser induced fluorescence

Rotational analyses are reported for the and bands of the transition of C2H2 near 45,000 cm−1 (+2800 cm−1 relative to T 0) from jet-cooled laser-induced fluorescence spectra. While the band is unperturbed and straightforward to assign, the 11 level is strongly perturbed by interactions with the 21 B 2 polyad, where υ B ′ = υ4′ + υ6′. In order to assign the lines of this band, a population-labelling technique was used, employing an infrared laser to deplete the population in selected ground state rotational levels before probing with the ultraviolet laser. Deperturbation of the 11/21 B 2 interaction leads to the value cm−1 for the fundamental symmetric C–H stretching frequency. Assignments are also reported for the 23 and 1121 levels, completing all assignments of levels containing excitation in only the totally symmetric vibrational modes up to +4500 cm−1. The reassignment of implies that some of currently accepted assignments above 47,000 cm−1 are in error and suggests that the interpretation of some aspects of the near-threshold photodissociation measurements of Mordaunt et al. [J. Chem. Phys. 108, 519 (1998)] may need to be revisited.

High Resolution FTIR and Diode Laser Supersonic Jet Spectroscopy of the N = 2 HF Stretching Polyad in (HF)2 and (HFDF): Hydrogen Bond Switching and Predissociation Dynamics

We report Fourier transform infrared (FTIR) and high resolution diode laser spectra (∼ 1MHz instrumental bandwidth) obtained in cooled absorption cells as well as in a supersonic jet expansion for the N = 2 polyad region of the HF-stretching vibrations of (HF)2, HFDF and DFHF. Three vibrational transitions have been observed for (HF)2 and two for both monodeuterated isotopomers. For (HF)2 we have identified and analysed the observed transitions of the polyad member 22 of the type Δ K a = 0 and Δ K a = ± 1 up to rotational sublevel Δ K a = 3. Band centers as well as rotational constants of all four K a states have been determined. The tunneling splittings due to hydrogen bond switching for these four K a states have been investigated, with the Δ K a = 0 up to Δ K a = 2 sublevels having tunneling symmetry Γ vt = A + for the lower tunneling states, and switching periods ranging from 158ps for K a = 0 to 1.35ns for K a = 2. A tunneling level inversion is found at Δ K a = 3, leading to a symmetry Γ vt = B + for the lower tunneling state of this K a-sublevel. The vibrational assignment of the measured spectra of (HF)2 was established by comparison with the monodeuterated isotopomers HFDF and DFHF. For HFDF we have identified and analysed five subbands between 7600cm-1 and 7730cm-1. We have determined the spectroscopic constants of the rotational levels Δ K a = 0 and Δ K a = 1 for the vibrationally excited state and of the levels of Δ K a = 1 and Δ K a = 2 of the ground state, the latter from combination differences. From the measurements in a supersonic jet expansion we determined the predissociation line width of the N = 22, K a = 1 to be about 120MHz for the Γ vt = A + tunneling state of (HF)2 and about 90MHz for Γ vt = B +. For the Δ K a = 0 level of N = 22 we obtained predissociation line widths ranging around 100MHz, similar to those of the Δ K a = 1 level. In the case of HFDF, the predissociation line width of Δ K a = 1 is about 80MHz. Predissociation lifetimes for these levels with the unbonded HF stretching excited thus are in the range of about 1 to 2ns. The predissociation width in the N = 21 level is uncertain by about a factor three with lg(Δν/MHz) = (3 ± 0.5) and in N = 23 it is about 600MHz corresponding to rounded lifetimes of 0.1ns and 0.3ns when the bonded HF stretching is excited thereby demonstrating strongly mode selective predissociation rates in the N = 2 polyad. Under thermal equilibrium conditions we derived the pressure broadening coefficient for (HF)2 (γ = (6 ± 1) × 10-4cm-1/mbar in the wavenumber range between 7713cm-1 and 7721cm-1 for total gas pressures between 10 and 60mbar, all values as full widths half maximum). For absolute frequency calibrations we have remeasured the first overtone transitions of the monomer HF with much improved precision between P(5) (7515.80151cm-1) and R(7) (7966.22188cm-1).

Development of a Supercritical Fluid Jet Technique for Supersonic Jet Laser Spectroscopy of Nonvolatile and Pyrolytic Molecules

Abstract A new supersonic jet technique, for nonvolatile and pyrolytic molecules, such as biomolecules, called the supercritical fluid jet (SCF-jet) technique was developed. This method enables the vaporization of such molecules without hard heating. To demonstrate the SCF-jet technique, we applied it to 1-naphthol and measured the resonant enhanced multiphoton ionization spectrum.

Laser spectroscopy of clusters: Application to differentiation of chiral systems

Laser spectroscopic studies of isolated clusters formed in supersonic beams coupled to resonance enhanced multiphoton ionization, have demonstrated the potentiality of this method to obtain information on the physicochemical properties of a large variety of clusters. We have recently applied this laser supersonic jet technique to study chiral molecules and to enantiodifferentiation their omo and eteroclusters. In this paper, results on measurements of the binding energy of diastereomeric complexes of an aromatic chiral alcohol, the (R)-(+)-1-phenyl-1-propanol P R, with chiral sec-butanol S or R, n-butanol: N and H 2O are reported. It is shown that their binding energies range around 5–6 kcal/mol. Semiempirical calculations confirm that the difference in binding energy of these clusters depends on a balance between electrostatic and dispersive forces.

Identification of the OC–IH isomer based on near-infrared diode laser spectroscopy

The near-infrared ν 2+ ν 5 1 combination bands of OC–HI and its isomeric form OC–IH have been recorded using a high-frequency wavelength modulation diode laser supersonic jet spectrometer. In addition, the ν 2 spectral region has been reinvestigated, leading to the assignment of the ν 2 fundamental in the isomeric species, OC–IH. The ν 1 band of OC–HI has also been rovibrationally assigned. The results are used to give qualitative information concerning the nature of molecular dynamics in this complex and its relation to that of other members in the homologous series OC:HX (X=F, Cl, Br, and I).

A study of the intermolecular ν 51 vibration in OCH 35Cl based on near infrared spectroscopy

The near infrared ν 2 + ν 5 1 combination bands of OCH 35Cl and OCH 37Cl have been recorded using a high frequency wavelength modulation diode laser supersonic jet spectrometer. In addition, the static gas phase spectra of the associated ν 2 + ν 5 1 − ν 5 1 and ν 2 + 2 ν 5 2 − 2 ν 5 2 hot bands in OCH 35Cl have been recorded using Fourier transform infrared absorption spectroscopy. The combined results permitted the evaluation of the band origin of 48.9944(2) cm −1, a rotational constant of 0.0565731(6) cm −1, a distortion constant of 1.906 × 10 −7(6) cm −1, and the Coriolis coupling constant of 0.0001466(2) cm −1 for the low frequency intermolecular bending vibration of the OCH 35Cl isotopomer.

Tandem time-of-flight mass spectrometer for cluster–surface scattering experiments

A new tandem time-of-flight mass spectrometer is described which is designed to study the mass-, velocity-, and angle-resolved scattering of cluster ions from solid surfaces. Clusters are produced in a supersonic jet laser desorption/vaporization source, ionized either directly in the formation step or by subsequent photoionization of neutrals, mass selected in a primary time-of-flight region, and decelerated to the impact energy (50–1000 eV) close to the target surface. Cluster–surface collisions take place in a field-free region in order to determine both velocity and angular distributions of the scattered clusters and fragments with an independently pulsed, rotatable secondary time-of-flight mass spectrometer. Several surface targets can be mounted in the UHV scattering chamber (10−10 Torr base pressure) on a five-axis manipulator which, together with the rotatable secondary TOF, allows for independent variation of incident and scattering angles. Target surfaces can be cleaned by direct current heating and sputtering with an argon-ion gun. Surface structure and composition are assessed by low-energy electron diffraction (LEED) and Auger spectroscopy with a four grid reverse view LEED/Auger system. Surface collision experiments of fullerenes (C+60, C+70, C+76, C+84, ...) and metallofullerenes (La@C+82) with highly oriented pyrolitic graphite (HOPG) surfaces are described as examples for the performance of the instrument. Effects of surface contamination in the scattering of fullerenes from HOPG are described to demonstrate the need for thorough cleaning procedures in order to obtain reproducible results. © 1995 American Institute of Physics.

A near-infrared Fourier-transform planar supersonic jet spectrometer for rovibrational studies of weakly bound dimers and trimers

A high-resolution FTIR supersonic slit jet absorption spectrometer is described for the investigation of weakly bound dimers and trimers in the near-infrared spectral region. The spectrometer is demonstrated to conservatively have a sensitivity of 6×108 molecules/cc/state and can be operated at an apodized resolution of 0.004 cm−1. To illustrate the performance of the spectrometer, it has been applied to the rovibrational analysis of the band spectra of three weakly bound species in the near infrared: ν1 OC–HF, ν1 N2–HCl, and ν5 (H35Cl)3. The recorded spectra of these species are compared with corresponding investigations using state-of-the-art tunable infrared laser supersonic jet or molecular-beam spectrometers to illustrate the capabilities and limitations of the current FTIR supersonic jet spectrometer.

Recent Advances in Rovibrationally Resolved FTIR Supersonic Jet Spectroscopy of Transients, Weakly Bound Dimers and Trimers

AbstractRecent advances in the development and application of a highly sensitive near infrared FTIR supersonic jet spectrometer are reported. Investigations of: v1 OC‐HF; ν1, ν2 OC‐HCl; ν1 +, ν2 ± (HCl)2; ν1, ν1±ν21 Ar‐HCl and ν1 N2‐HCl will be presented. In specific cases, a direct comparison with corresponding spectra recorded using tunable near infrared laser supersonic jet and molecular beam absorption spectrometers will be made to illustrate the current capabilities and limitations of the FTIR supersonic jet spectrometer. As an example of the application of the technique to clusters, we report a study of the ν5 HCl asymmetric stretching band in the trimer, (HCl)3. Some preliminary studies of discharge‐generated species will also be reported using the jet spectrometer. The latter include: i) the investigation of vibrational hot bands in CO and ii) A2Π3/2,1/2→X2Σ+ rovibronic transitions in the CN radical.

Investigation of the ground vibrational state structure of H35Cl trimer based on the resolved K, J substructure of the ν5 vibrational band

The high resolution rovibrational IR spectrum of the antisymmetric H35Cl stretching ν5 vibrational band in the (H35Cl)3 isotopomer of the trimer has been measured with a tunable infrared diode laser supersonic jet spectrometer. One of the most prominent features of the spectrum is a series of strong lines each formed with pP or rR transitions, with resolved K, J substructure developing between two adjacent pP or rR heads. Analyzing the spectrum of (H35Cl)3 as the perpendicular band of an oblate symmetric rovibrator, the following molecular parameters have been obtained: ν0−C′ζ=2809.776 98(6) cm−1, B″=6.804 14(55)×10−2 cm−1, B′=6.859 43(55) ×10−2 cm−1, C′–C″=2.737(78)×10−4 cm−1, DJK″=−8.40(38)×10−7 cm−1, DJK′=−8.14(38)×10−7 cm−1, DJ″=4.26(16)×10−7 cm−1, DJ′=4.16(16)×10−7 cm−1, DK″=4.32(22)×10−7 cm−1, DK′=4.16(22)×10−7 cm−1. A relationship among the centrifugal distortion constants establishes that the geometry of (H35Cl)3 is consistent with a dynamically averaged planar ground vibrational state. The centers of mass of the H35Cl components are separated by 3.693(1) Å in this structure. Ab initio methods were also used to estimate the splitting due to the tunneling motions between clockwise (cw) and counterclockwise (ccw) identical structures. Both theoretical and experimental evidence indicate that the (HCl)3 complex has a planar equilibrium structure with no observable tunneling probability between the cw and ccw forms, thus the molecular symmetry group of the complex is proposed to be C3h(M).

Geometry and torsional motion of biphenyl in the ground and first excited singlet state

The lowest excited singlet state of biphenyl (BP) and a number of its isotopically and chemically substituted analogs have been studied by supersonic jet laser spectroscopy. The symmetry species of this excited state in BP can be classified as B+2u in the G16 extended molecular symmetry group G16 (EM). The symmetry-allowed origin of the biphenyl -h10 S1←S0 electronic transition occurs at 35 268 cm−1. The frequency of the torsional motion in S1 is determined to be ∼65 cm−1. The potential parameters for this motion in S1 are V2=1195 cm−1, V4=−190 cm−1, and V6=18 cm−1. The torsional motion for the ground state (∼50 cm−1) can be described by V2=50 cm−1 and V4=−148 cm−1. The change in the dihedral angle between the two benzene rings in BP upon S0 to S1 excitation is determined to be ∼44° based on a Franck–Condon factor calculation. Several fundamentals of the molecular vibrations are assigned in the S1 state. The exciton interaction between the coupled benzene rings in biphenyl is suggested to be large (>103 cm−1).