Hexapole state-selection and orientation of asymmetric top molecules: CH2F2

Molecular beams of the b-type asymmetric top molecule methylenefluoride (CH2F2) were focused and rotationally state-selected with an electrostatic hexapole. The focusing behavior is mediated by the dependence of rotational energy on electric field strength, the Stark effect. The matrix quantum theory needed to calculate the rotational energies of asymmetric top molecules within an electric field are summarized. These Stark energies were calculated and parameterized for the lowest 165|JτM〉 rotational levels of CH2F2. Excellent agreement was found between classical trajectory simulations incorporating these calculated energies and experimentally measured hexapole focusing spectra. Based on this agreement, the rotational state distribution transmitted by the hexapole as a function of hexapole voltage has been ascertained. Comparisons are made with simulated focusing spectra of the a-type rotor, formaldehyde (H2CO). The theoretical formalism needed to describe the orientational probability distribution functi...

[1]  E E Witmer.  The Quantization of the Rotational Motion of the Polyatomic Molecule by the New Wave Mechanics. , 1927, Proceedings of the National Academy of Sciences of the United States of America.

[2]  T. J. Curtiss,et al.  Hexapole-selected supersonic beams of reactive radicals: CF3, SiF3, SH, CH, and C2H , 1998 .

[3]  M. Janssen,et al.  Steric effects on electronically excited product channels in reactions between Ca(D-1(2)) and CH(3)X(JKM) (X=Cl, Br) , 1996 .

[4]  M. Mizushima.  Theory of the Stark Effect of Asymmetric Rotator with Hyperfine Structure , 1953 .

[5]  P. R. Brooks,et al.  Focusing and Orienting Asymmetric‐Top Molecules in Molecular Beams , 1970 .

[6]  J. B. Milan,et al.  Electric field dependence of reactivity of state‐selected and oriented methylhalides , 1991 .

[7]  Seung E. Choi,et al.  Oriented molecule beams: pulsed, focused beams of methyl halides in pure JKM rotational states , 1986 .

[8]  Curtiss,et al.  Asymmetry of the polarized-laser-induced photofragmentation of oriented CH3I molecules. , 1987, Physical review letters.

[9]  S. Golden,et al.  The Stark Effect for a Rigid Asymmetric Rotor , 1948 .

[10]  S. Golden,et al.  An Asymptotic Expression for the Energy Levels of the Asymmetric Rotor. III. Approximation for the Essentially Degenerate Levels of the Rigid Rotor , 1949 .

[11]  Gilbert W. King,et al.  The Asymmetric Rotor I. Calculation and Symmetry Classification of Energy Levels , 1943 .

[12]  R. Anderson.  Tracks of Symmetric Top Molecules in Hexapole Electric Fields , 1997 .

[13]  G. W. King,et al.  The Asymmetric Rotor. VII. Extension of the Calculation of Energy Levels , 1949 .

[14]  S. Golden.  An Asymptotic Expression for the Energy Levels of the Asymmetric Rotor. II. Centrifugal Distortion Correction , 1948 .

[15]  R. Bernstein,et al.  Crossed beam reaction of oriented methyl iodide with rubidium: Steric factor and reactive asymmetry versus scattering angle , 1982 .

[16]  M. Janssen,et al.  IMAGING OF ORIENTED MOLECULES , 1997 .

[17]  Thomas J. Curtiss,et al.  Rotational State Selection and Orientation of OH and OD Radicals by Electric Hexapole Beam-Focusing , 1997 .

[18]  H. Loesch,et al.  Reactive Scattering from Brute Force Oriented Asymmetric Top Molecules: K + C6H5I → KI + C6H5 , 1997 .

[19]  S. Wang,et al.  On the Asymmetrical Top in Quantum Mechanics , 1929 .

[20]  M. Weida,et al.  Practical Aspects of Aligning Asymmetric Top Molecules via Single-Photon Excitation: An Application to S1 ← S0 Excitation of Glyoxal , 1997 .

[21]  H. Jalink,et al.  Polarized emission from the products of oriented reactants: The Ba+N2O→BaO*+N2 reaction , 1986 .

[22]  S. Stolte,et al.  Hexapole state selection and focusing vs. brute force orientation of beam molecules , 1995 .

[23]  H. J. Loesch,et al.  Brute Force Orientation of Asymmetric Top Molecules , 1997 .

[24]  N. Butkovskaya,et al.  Mass-spectrometric analysis of the polar molecules beam.: I. Focusing in inhomogeneous electric field , 1976 .

[25]  K. Schreel,et al.  State-to-state scattering of oriented OH , 1997 .

[26]  S. R. Gandhi,et al.  Focusing and state selection of NH3 and OCS by the electrostatic hexapole via first‐ and second‐order Stark effects , 1987 .

[27]  D. Ende,et al.  The influence of the internal state and translational energy of the molecular reactant upon the chemiluminescent reaction Ba + N2O → BaO* + N2 , 1986 .

[28]  S. R. Gandhi,et al.  Oriented molecule beams: focused beams of rotationally cold polar polyatomic molecules , 1987 .

[29]  S. Golden.  An Asymptotic Expression for the Energy Levels of the Rigid Asymmetric Rotor , 1948 .

[30]  D. Ende,et al.  The influence of the orientation of the NO molecule upon the chemiluminescent reaction NO+O3→NO2*+O2 , 1984 .

[31]  C. Bernstein,et al.  Chemical Dynamics via Molecular Beam and Laser Techniques: The Hinshelwood Lectures, Oxford, 1980 , 1982 .

[32]  L. F. Phillips,et al.  Electron transfer to oriented molecules: K+CF3I and K+CH3I , 1990 .

[33]  M. Janssen,et al.  Steric properties of the reactive system calcium(1D2) + fluoromethane (JKM) .fwdarw. calcium fluoride (A) + methyl , 1991 .

[34]  D. Ende,et al.  Influence of translational and internal energy upon the chemiluminiscent part of the exothermic reaction NO + O3 → NO*2 + O2 → NO2 + hν + O2 , 1980 .

[35]  Walter Gordy,et al.  Microwave Molecular Spectra , 1970 .

[36]  Seung E. Choi,et al.  Theory of oriented symmetric‐top molecule beams: Precession, degree of orientation, and photofragmentation of rotationally state‐selected molecules , 1986 .