Diffraction Signals of Aligned Molecules in the Gas Phase:  Tetrazine in Intense Laser Fields

Abstract

We performed a theoretical study of the electron diffraction patterns that arise from aligning a molecule, s-tetrazine (C2N4H2), in a high intensity laser field using the Friedrich−Herschbach approach. The molecule is modeled using geometries and zero-point vibrations from a coupled-cluster level ab initio calculation. The alignment is achieved by a circularly polarized, quasicontinuous high-intensity laser pulse that intersects the molecular sample at selected geometries. The molecular ensemble is taken to be at a rotational temperature of 5 K. We find that even at 1 TW/cm2 there is a very noticeable effect on the diffraction pattern stemming from the alignment. Moreover, using different laser geometries, it is possible to observe different diffraction patterns corresponding to specific projections of the molecular geometry onto the Fourier plane of the detector, making the laser a kind of “optical goniometer.” Predictably, higher alignment laser intensities lead to narrower orientational distributions, which in turn provide for diffraction patterns with larger modulation depths. We find, however, that for small diffraction angles (s ≤ 15 Å-1) the effect appears to saturate at an alignment laser intensity of about 4 TW/cm2. This suggests that there is a window of opportunity where alignment is very beneficial for extracting information from gas-phase diffraction patterns and where detrimental multiphoton processes do not yet compromise the interpretation of the molecular structure.

Strong-field rescattering physics—self-imaging of a molecule by its own electrons

“…If molecules can be aligned or oriented, clearly, not only the interatomic distances can be determined but also the bond angles [160] in the molecule. Gas phase molecules can be aligned either by photodissociation with femtosecond laser pulses or by active laser alignment techniques [108,[161][162][163]. Today, infrared or MIR lasers with a pulse duration less than 10 fs are readily available.…”

Rotational molecular dynamics of laser-manipulated bromotrifluoromethane studied by x-ray absorption

“…Additionally, our research lays the foundation for molecular imaging of laser-aligned molecules using xray diffraction. 15,16 In addition to the analytical value of the x-ray absorption probe, laser-induced molecular alignment opens up a way to control x-ray absorption in an ultrafast (picosecond) way. This means that by controlling the alignment of the molecules in a gas sample, we are able to control how much flux of an incident x-ray pulse is transmitted by the gas.…”

STRUCTURAL DYNAMICS OF FREE MOLECULES AND CONDENSED MATTER. Part I. THEORY AND EXPERIMENTAL TECHNIQUE

“…These concepts can be readily extended to the diffraction signatures of larger vibrating polyatomic molecules. In the papers [40][41][42] it have been calculated the patterns expected when the cyclic, 6-atomic aromatic ring molecule s-tetrazine (C 3 H 3 N 3 ) is excited to specific vibrations in its electronically excited state S 1 . Fig.…”

“…If the pulse laser pump has a form of δ-function at t = 0, the temporal dependence of the molecular intensity will be: sM(s, t) = g(s) ∫(sin (sR)/R)P(R, t)dR. (39) When the form of the probing electron pulse is approximated by the Gaussian function with the central point t = t 0 and corresponding duration of τ, the averaged molecular intensities can be written as: sM(s,t) τ = (2πτ 2 ) -½ ∫ exp[-(t-t 0 ) 2 /2τ 2 ] sM(s,t) dt (40) Using the above theory, time-dependent molecular scattering intensities and the corresponding radial distributions of internuclear distances in the ICN photodissociation processes were calculated [84], Fig. 9 (please, see Reference [83] for comparison of results).…”