Molecular Beam Spectroscopy Research Articles

Infrared and microwave spectra of OCO–HF and SCO–HF

The H–F stretching bands of the OCO–HF and SCO–HF complexes have been studied by optothermal (bolometer-detected) molecular-beam spectroscopy. Both species exhibit spectra of a quasilinear molecule red shifted from free HF by 52.1 and 57.5 cm−1, respectively. The principal band in both molecules is accompanied by a slightly red-shifted doublet-type subsidiary band that can be interpreted as a hot band of a low frequency bending vibration or a K=1 subband of a bent molecule. Accurate doublet splittings in the ground H–F vibrational state have been measured by pulsed-nozzle Fourier-transform microwave spectroscopy.

Supersonic molecular beam and static gas phase spectroscopy of intermolecular hot bands associated with ν 116O 12C--- 1H 19F

Gas phase rovibrational analysis of the ν 1 (H stretching vibration) and its associated hot bands ν 1+ν 3−ν 3, ν 1 + ν 5 1−ν 5 1 and ν 1 + 2ν 5, −2ν 5 are investigated using a broadband tunable color center laser spectrometer. Rotational and distortion constants associated with the low frequency intermolecular stretching (ν 3) and bending (ν 5 1) states are determined to be for ν 3: B=0.100786(28) cm −1, D itJ=3.36(30)×10 −7 cm −1; and for ν 5 1: B=0.1029736(93) cm −1, D J =3.598(41)×10 −7 cm −1 q=0.000235(15) cm −1. The precisely evaluated band origin frequencies permit determination of two anharmonic cross terms associated with the hydrogen bond hypersurface x 13 = 8.634(20) and x 15 = 5.4099(6) cm −1.

Hyperfine structure near the 13–1 band head in the B–X transition of ^127I_2

Hyperfine structure of the rovibronic transitions R(0)–R(10) and P(1)–P(5) in the 13–1 band belonging to the B–X system of 127I2 was studied by rectangular-crossing molecular-beam laser spectroscopy. The full width at half-maximum of the observed lines was 5 MHz, which corresponds to a resolving power of 108. Not only allowed transitions ΔF = ΔJ but forbidden transitions ΔF = 0 and ΔF = −ΔJ were identified, and absolute hyperfine coupling constants of the rovibronic states (J = 0–10) in the B(v′ = 13)−X(v″ = 1) transition were determined. In addition, the relative line strength of each hyperfine transition was compared with the theoretical value.

The lowest-frequency bending mode (ν 71) of HCN-HF from near-infrared laser spectroscopy

The lowest intermolecular bending frequency of HCN-HF has been determined in both the ground (73.583(3) cm −1) and excited (73.176(3) cm −1) CH vibrational states using near-infrared laser molecular beam spectroscopy. The results also show that the vibrational predissociation lifetime is weakly dependent on the intermolecular bending state.

ChemInform Abstract: Laser Desorption Molecular Beam Spectroscopy: The Electronic Spectra of Tryptophan Peptides in the Gas Phase

ChemInformVolume 19, Issue 3 Physical Organic Chemistry ChemInform Abstract: Laser Desorption Molecular Beam Spectroscopy: The Electronic Spectra of Tryptophan Peptides in the Gas Phase J. R. CABLE, J. R. CABLE Dep. Chem., Univ. Chicago, Chicago, IL 60637, USASearch for more papers by this authorM. J. TUBERGEN, M. J. TUBERGEN Dep. Chem., Univ. Chicago, Chicago, IL 60637, USASearch for more papers by this authorD. H. LEVY, D. H. LEVY Dep. Chem., Univ. Chicago, Chicago, IL 60637, USASearch for more papers by this author J. R. CABLE, J. R. CABLE Dep. Chem., Univ. Chicago, Chicago, IL 60637, USASearch for more papers by this authorM. J. TUBERGEN, M. J. TUBERGEN Dep. Chem., Univ. Chicago, Chicago, IL 60637, USASearch for more papers by this authorD. H. LEVY, D. H. LEVY Dep. Chem., Univ. Chicago, Chicago, IL 60637, USASearch for more papers by this author First published: January 19, 1988 https://doi.org/10.1002/chin.198803040Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue3January 19, 1988 RelatedInformation

Laser Spectroscopy of Molecules and Clusters

The advantages of collimated cold supersonic beams for sub-Doppler laser spectroscopy of molecules and small clusters are discussed and illustrated by several examples. These include sub-Doppler spectroscopy of the SO2 molecule in the ultraviolet and of NO2 in the visible region. Lifetime measurements under collision-free conditions, stepwise excitation of high lying molecular Rydberg states, and sub-Doppler double resonance spectroscopy of Na3 demonstrate the achievements possible by combining molecular beam techniques with various methods of laser spectroscopy. The relevance of the experimental results for our understanding of the dynamics of molecules in excited states and for the development of new theoretical approaches is emphasized. Some sensitive detection techniques are presented which are in particular useful when cw lasers are used for spectroscopy in cw molecular beams at low densities.

Multiphoton ionization and fragmentation study of acetone at XeCl excimer laser radiation

Multiphoton ionization and fragmentation of the acetone molecule at 308 nm laser radiation are studied using diffuse molecular beam and multiphoton ionization mass spectroscopy. It is found that the ion peaks of acetone do not appear at m/e = 58, but only at m/e = 15 and 43, corresponding respectively to the two neutral fragments CH 3 and CH 3CO generated by the photodissociation of acetone. The intensities of these ions are proportional to the 3.6th and 3.0th power of the laser intensity, respectively.

Laser desorption molecular beam spectroscopy: the electronic spectra of tryptophan peptides in the gas phase

Laser desorption molecular beam spectroscopy: the electronic spectra of tryptophan peptides in the gas phase

Summary Abstract: Adsorption and reaction of oxygen on Si(100): A modulated molecular beam and time-resolved x-ray photoelectron spectroscopy study

First Page

Spectroscopic observation of phase coexistence in SF6-Arn clusters for n=10-20.

In infrared photodepletion spectroscopy of molecular beams of $\mathrm{S}{\mathrm{F}}_{6}\ensuremath{-}{\mathrm{Ar}}_{n}$ clusters, a shifting and broadening of the ${\ensuremath{\nu}}_{3}$ band of S${\mathrm{F}}_{6}$ was observed by Gough, Knight, and Scoles for a narrow range of experimental conditions. A Monte Carlo simulation of those spectra based on an instantaneous dipoleinduced dipole model reproduces them semiquantitatively and shows that such broadening can be caused by phase coexistence. However, cluster-size distribution effects make it nuclear whether this is the source of the broadening observed in the existing data.

Rabi oscillations and rapid-passage effects in the molecular-beamCO2-laser Stark spectroscopy ofCH3F

Sub-Doppler molecular-beam laser Stark spectroscopy has been employed to produce high-contrast Rabi oscillations in the ${\ensuremath{\nu}}_{3}$ band of ${\mathrm{CH}}_{3}$F. By varying the intensity of the cw ${\mathrm{CO}}_{2}$ laser, up to five complete oscillations were observed before the phenomenon was washed out by rapid-passage effects and damping mechanisms. Besides being useful in clarifying key features of coherent ir molecular-beam spectroscopy, the observation of Rabi oscillations provides one of the most accurate means of directly measuring transition dipole moments. Analysis of the present data on three rovibrational transitions, Q(1,1) -1\ensuremath{\leftarrow}0, P(1,0) 0\ensuremath{\leftarrow}0, and R(1,1) 0\ensuremath{\leftarrow}1, has yielded a rotationless transition dipole moment of 0.21\ifmmode\pm\else\textpm\fi{}0.01 D for the ${\ensuremath{\nu}}_{3}$=1\ensuremath{\leftarrow}0 vibration. This result is in agreement with values estimated from both band-intensity and absorption-coefficient data in the literature.

Molecular-beam infrared absorption studies of rare gas-ocs complexes

Resolved vibration-rotation spectra for Ne·OCS, Ar·OCS and Kr·OCS in the ν 3 region of the OCS monomer have been obtained by absorption spectroscopy of pulsed molecular beams. Rotational constants for the upper and lower vibrational states and the band origins were determined, and effective structures for these molecules were calculated.

Time-resolved auger electron spectroscopy combined with modulated molecular beam techniques for gas-surface reaction kinetics studies

An Auger electron spectrometer is combined with a modulated molecular beam system and the time-dependent concentration of adsorbed oxygen on a molybdenum surface subject to a chopped O 2 beam is measured and compared to predictions of a reaction kinetic model derived from modulated molecular beam spectroscopy alone.

Resonant two-photon ionization spectroscopy in supersonic beams for discrimination of disubstituted benzenes in mass spectrometry

Supersonic molecular beam spectroscopy has great potential for selectivity in chemical analysis. In this work we have used resonant two-photon ionization (R2PI) spectroscopy in supersonic beams of argon as a means of obtaining ultraviolet ionization spectra with sharp features for unique identification of species in a mixture. This technique, therefore, provides a wavelength-selective means of forming ions for detection in time-of-flight mass spectrometry. The spectroscopy of several disubstituted benzenes including p-cresol, p-toluidine, p-aminophenol, p-fluoroaniline, p-fluorophenol, and hydroquinone has been studied near their origin transitions. These molecules have low quantum yields in fluorescence but can be detected with great sensitivity (< 20 ppb) by using laser ionization. On the basis of the separation between spectral lines of compounds in various mixtures, we estimate the combined maximum discrimination possible in a mass spectrometer, thus demonstrating the capability of this technique for identification. When this method is used, an experimental discrimination between p-cresol and p-fluoroaniline on the order of 1:5000 can in principle be obtained.

Coulomb Excitation of 7Li

Coulomb excitation of the 0�478 MeV, J1t = t-, first excited state of 7Li has been studied using beams of 7Li ions and targets of 138Ba and 208Pb. Spectra of the scattered particles were measured at 171� using an annular Si surface-barrier detector (l 38Ba and 208Pb targets) and at 90� using an Enge split-pole magnetic spectrometer (208Pb targets). For each experimental configuration, the bombarding energy at which nuclear interference became significant was determined experimentally. An analysis based upon the reorientation effect yielded the following results: the static electric quadrupole moment of the J1t = t- ground state (Q3/2-) is -4�0� 1�1 efm", the contribution of the giant dipole resonance (GDR) to the Coulomb-excitation cross section is 2�7 �0�2 times as great as would be calculated from the hydrodynamic model, and B(E2;t-~t-) is 7�42�0�14e2fm4 ? The value obtained for Q3/2- is in excellent agreement with results reported from atomic- and molecular-beam spectroscopy and from Coulomb scattering of aligned 7Li. Thus it provides a strong verification of the validity of the reorientation-effect technique for the determination of nuclear quadrupole moments, provided that the GDR effect is treated adequately.

Microwave spectroscopy of supersonic molecular beams: Single- and double-resonance experiments with OCS and HCCCN

By applying the principles of microwave Stark modulated spectroscopy to continuous supersonic beams a new technique for high-resolution rotational spectroscopy has been developed. The capabilities of the new technique have been demonstrated through investigations of the spin-rotation splittings in O13CS and HCCCN. Simultaneously the method allowed a diagnostic of supersonic molecular beams. Relative beam intensities, supersonic flow velocities and translational temperatures of pure and seeded beams were determined from spectroscopic measurements of signal intensities, Doppler shifts and line widths, respectively. Microwave-microwave double-resonance experiments established deviations from the Boltzmann populations of rotational energy levels in supersonic molecular beams.

High-resolution molecular-beam spectroscopy of NaCN and Na13CN

The sodium cyanide molecule was studied by molecular-beam electric-resonance spectroscopy in the microwave region. We used the seeded-beam technique to produce a supersonic beam with strong translational, rotational and vibrational cooling. In the frequency range 9.5–40 GHz we observed and identified for NaCN 186 and for Na13CN 107 hyperfine transitions in 20 and 16 rotational transitions, respectively, all in the ground vibrational state. The rotational, the five quartic and three sextic centrifugal distortion constants of NaCN are: A″ = 57921.954(7) MHz; B″ = 8369.312(2) MHz, C″ = 7272.712(2) MHz. All quadrupole and several spin-rotation coupling constants for the hyperfine interaction were evaluated. The quadrupole coupling constants (in MHz) for NaCN are: eQq12(Na) = −5.344(5), eQq12 = 2.397(7). eQq12(N) = 2.148(4), eQq12(N) = −4.142(5). From these constants and those of Na13CN we have determined the principal components of the quadrupole coupling tensor for potassium and nitrogen. The structure of sodium cyanide evaluated from the rotational constants of NaCN and Na13CN was found to be T shaped, similar to the structure of KCN but completely different from the linear isocyanide configuration of LiNC. The effective structural parameters for sodium cyanide in the ground vibrational state are: rCN = 1.170(4) Å, rNaC = 2.379(15) Å, rN12N = 2.233(15) Å, in gratifying agreement with ab initio calculations. Both the geometrical structure and the hyperfine coupling justify the conclusion that the CN group in gaseous sodium cyanide approximately can be considered as a free CN− ion.

High-resolution molecular-beam spectroscopy on the A 2Σ 1/2+, ν=0 state of SH

In a molecular-beam laser-induced fluorescence experiment on SH, the hyperfine and spin—rotation structure in the A 2Σ 1/2 +, ν=0 state has been determined. From linewidth measurements, a rotationally dependent predissociation is shown to be present. A natural lifetime of 3.2 ± 0.3 ns is obtained for N=0.

Infrared laser spectroscopy of molecular beams using a room-temperature beam detector: Application to the study of translational freezing in free-jet expansions

A simple and inexpensive alternative to the liquid He bolometer for observing laser induced vibrational excitation in molecular beams is reported. A room-temperature pyroelectric detector is used to directly measure the increase in molecular energy resulting from laser excitation. With this detector, line broadening effects have been used to study translational freezing in free-jet expansions.

Internal rotation in methyl silane by avoided-crossing molecular-beam spectroscopy

The avoided-crossing molecular-beam electric-resonance technique was applied to methyl silane in the ground torsional state. A new type of anticrossing is introduced which breaks the torsional symmetry and obeys the selection rules Δ J = 0, K = +1 / a3 −1. For these “barrier” anticrossings, the values of the crossing fields E c yield directly the internal rotation splittings; the E c are independent of the difference ( A- B) in the rotational constants. Such anticrossings were observed for J from 1 to 6. Studies were also conducted of several “rotational” anticrossings ( J, K) = (1, ±1) / a3 (2, 0) for which E c does depend on ( A- B). The normal rotational transition ( J, K) = (1, 0) ← (0, 0) was observed in the ground torsional state using the molecular beam spectrometer. The present data on CH 3 28SiH 3 were combined with Hirota's microwave spectra and analyzed with the torsion-rotation Hamiltonian including all quartic centrifugal distortion terms. In addition to evaluating B and several distortion constants, determinations were made of the moment of inertia of the methyl top I α = 3.165(5) amu-Å 2, the effective rotational constant A eff = 56 189.449(32) MHz, and the effective height of the threefold barrier to internal rotation V 3 eff = 592.3359(73) cm −1. The correlations leading to these two effective constants are discussed and the true values of A and V 3 are determined within certain approximations. For the isotopic species CH 3 30SiH 3, barrier and rotational anticrossings were observed. The isotopic changes in A and V 3 were determined, as well as an upper limit to the corresponding change in I α .