Probing Proton Dynamics in Molecules on an Attosecond Time Scale

We demonstrate a technique that uses high-order harmonic generation in molecules to probe nuclear dynamics and structural rearrangement on a subfemtosecond time scale. The chirped nature of the electron wavepacket produced by laser ionization in a strong field gives rise to a similar chirp in the photons emitted upon electron-ion recombination. Use of this chirp in the emitted light allows information about nuclear dynamics to be gained with 100-attosecond temporal resolution, from excitation by an 8-femtosecond pulse, in a single laser shot. Measurements on molecular hydrogen and deuterium agreed well with calculations of ultrafast nuclear dynamics in the H2+ molecule, confirming the validity of the method. We then measured harmonic spectra from CH4 and CD4 to demonstrate a few-femtosecond time scale for the onset of proton rearrangement in methane upon ionization.

[1]  J. Levesque,et al.  Tomographic imaging of molecular orbitals , 2004, Nature.

[2]  L'Huillier,et al.  Attosecond Pulse Trains Using High-Order Harmonics. , 1996, Physical review letters.

[3]  P. Corkum,et al.  Probing molecular dynamics with attosecond resolution using correlated wave packet pairs , 2003, Nature.

[4]  P. Knight,et al.  Interference effects in high-order harmonic generation with molecules , 2002 .

[5]  H. G. Muller,et al.  Attosecond Synchronization of High-Harmonic Soft X-rays , 2003, Science.

[6]  P. Corkum,et al.  Deflection of Neutral Molecules using the Nonresonant Dipole Force , 1997 .

[7]  See Leang Chin,et al.  High harmonic generation in atomic and diatomic molecular gases using intense picosecond laser pulses-a comparison , 1994 .

[8]  K. F. Dunn,et al.  Photoionization of hydrogen and deuterium , 1995 .

[9]  Ernest R. Davidson,et al.  Potential energy surfaces of CH+4 , 1988 .

[10]  U. Kleineberg,et al.  Atomic transient recorder , 2004, Nature.

[11]  K. F. Dunn,et al.  The dissociative photoionization of methane in the VUV , 1999 .

[12]  Kanter,et al.  Direct determination of the stereochemical structure of CH4+ , 1986, Physical Review Letters.

[13]  P. Corkum,et al.  Plasma perspective on strong field multiphoton ionization. , 1993, Physical review letters.

[14]  P. Knight,et al.  Role of the intramolecular phase in high-harmonic generation. , 2002, Physical review letters.

[15]  M. Lein.  Attosecond probing of vibrational dynamics with high-harmonic generation. , 2005, Physical review letters.

[16]  E. Davidson,et al.  Experimental evidence for a C2v (2B1) ground-state structure of the methane cation radical: ESR and ab initio CI investigations of methane cation radicals (CH4+ and CD2H2+) in neon matrixes at 4 K , 1984 .

[17]  F. Légaré,et al.  Sub-laser-cycle electron pulses for probing molecular dynamics , 2002, Nature.