A quantum‐chemical perspective on the laser‐induced alignment and orientation dynamics of the CH₃X (X = F, Cl, Br, I) molecules

Abstract

Motivated by recent experiments, the laser-induced alignment-and-orientation (A&O) dynamics of the prolate symmetric top CH 3 X (X = F, Cl, Br, I) molecules is investigated, with particular emphasis on the effect of halogen substitution on the rotational constants, dipole moments, and polarizabilities of these species, as these quantities determine the A&O dynamics. Insight into possible control schemes for preferred A&O dynamics of halogenated molecules and best practices for A&O simulations are provided, as well. It is shown that for accurate A&O -dynamics simulations it is necessary to employ large basis sets and high levels of electron correlation when computing the rotational constants, dipole moments, and polarizabilities. The benchmark-quality values of these molecular parameters, corresponding to the equilibrium, as well as the vibrationally averaged structures are obtained with the help of the focal-point analysis (FPA) technique and explicit electronic-structure computations utilizing the gold-standard CCSD(T) approach, basis sets up to quintuple-zeta quality, core-correlation contributions and, in particular, relativistic effects for CH 3 Br and CH 3 I. It is shown that the different A&O behavior of the CH 3 X molecules in the optical regime is mostly caused by the differences in their polarizability anisotropy, in other terms, the size of the halogen atom. In contrast, the A&O dynamics of the CH 3 X series induced by an intense few-cycle THz pulse is mostly governed by changes in the rotational constants, due to the similar dipole moments of the CH 3 X molecules. The A&O dynamics is most sensitive to the B rotational constant: even the difference between its equilibrium and vibrationally-averaged values results in noticeably different A&O dynamics. The contribution of rotational states having different symmetry, weighted by nuclear-spin statistics, to the A&O dynamics is also studied.Irén Simk o and Kalyani Chordiya contributed equally to this work.

Diatomic molecule in a strong infrared laser field: level-shifts and bond-length change due to laser-dressed Morse potential

“…We derived analytic expressions, ( 18) and (19), which are valid in a wide wavelength range to account for the effect of a strong long laser pulse on the vibrational levels and the bond-length change of a diatomic molecule with high accuracy. These results can be readily applied both to heteronuclear and to homonuclear diatomic molecules and to certain (e.g.…”

“…In general, ionization-delay measurements are valuable tools to investigate the electronic properties of molecules [16]. An emerging topic in this field of research is molecules in strong IR fields without ionization [17], having obvious relevance also to important experimental techniques of laser manipulation of molecules, like trapping [18], alignment [19], orientation [20]. Ultra-high intensity laser pulses (10 18 -10 20 W cm −2 ) have a pedestal [21] typically in the intensity range of 10 10 -10 14 W cm −2 (having also an interesting nontrivial photon statistics [22]) which raises questions and concerns about the true "initial" state of the target molecule when the actual ultra-high intensity pulse reaches it.…”

Achieving high molecular alignment and orientation for CH$$_3$$F through manipulation of rotational states with varying optical and THz laser pulse parameters

“…The simulated molecular parameters show reasonable match with the experimentally reported values (given in parenthesis): (0.852 cm 32 ) and is 5.089 cm (5.182 cm 32 ), dipole moment ( ) of 1.894 D (1.850 D 33 ), polarizability as 2.524 Å and as 2.296 Å , computed at CCSD(T) 34 – 36 level of theory and the aug-cc-pVDZ basis set 37 , as implemented in the ORCA 4.1 package 38 , 39 . The computed molecular parameters can be improved further with higher level of theory, and using vibrational ground state geometry 40 . CH F is a symmetric top molecule, therefore, the rotational eigenfunctions transform as the irreducible representations (irreps) of D 41 .…”

An efficient and flexible approach for computing rovibrational polaritons from first principles

“…Such a perturbative approach was also applied in Ref. [49], and is a common practice for electronically non-resonant laser fields of moderate intensity [50][51][52][53][54]. Therefore, for IR cavity radiations, being off resonant with the electronic transitions, and for coupling strengths tipically realized in experiments [23,27], the perturbative treatment of electronic excitation seems to be a reasonable approach.…”