Mass-correlated rotational Raman spectra with high resolution, broad bandwidth, and absolute frequency accuracy

Abstract

We present mass-correlated rotational alignment spectroscopy, based on the optical excitation of a coherent rotational quantum wave and the observation of temporal wave interferences in a mass spectrometer. Combined electronic and opto-mechanical delays increased the observation time and energy resolution by an order of magnitude compared with preceding time-domain measurements. Rotational transition frequencies were referenced to an external clock for accurate absolute frequency measurements. Rotational Raman spectra for six naturally occurring carbon disulfide isotopologues were resolved with 3 MHz resolution over a spectral range of 500 GHz. Rotational constants were determined with single-kilohertz accuracy, competitive with state-of-the-art frequency domain measurements.

Structure of benzene from mass-correlated rotational Raman spectroscopy

“…For details about the absolute frequency calibration (a time domain equivalent to frequency comb spectroscopy), we refer the reader to our earlier work. 1 …”

“…The experimental technique of correlated rotational alignment spectroscopy is described in detail in our previous work. 1,52 Briefly, a pump pulse (800 nm, 100 μJ, 1 ps) from a 1 kHz amplified femtosecond Ti:Sa laser excited a coherent superposition of rotational states via rotational Raman excitation, creating a rotational wave packet. A time-delayed probe pulse (200 nm, 1 μJ, 45 fs) from a second 1 kHz Ti:Sa amplifier probed the evolution of the rotational wave packet via resonance enhanced two-photon ionization.…”

“…We recently developed mass-correlated rotational alignment spectroscopy (CRASY), a method for the mass-selective measurement of rotational Raman spectra with broad spectral range and MHz resolution. 1,2 The resolution represents an order-of-magnitude improvement over that of preceding rotational Raman or Fourier-transform IR spectroscopy (FTIR) 3,4 and the mass-correlation facilitates the analysis of multiple isotopologue spectra in a single data-set. Here we present rotational spectra for five benzene isotopologues, estimate effective and equilibrium bond lengths, discuss the possibility to determine isotope-specific bond lengths, and explain why preceding literature values were biased.…”

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

“…Different A&O realizations have been proposed and demonstrated, 1–4 such as adiabatic 5–8 and non‐adiabatic A&O, 9–13 A&O along one, 11,14,15 two, 6 or three dimensions, 16–19 using linearly 10,11,14 or circularly 15 polarized pulses, employing single 14,15 or multiple pulses, 9,10,16,18 utilizing optical 10,14,16 and/or terahertz (THz) 10,20,21 pulses, optical centrifuges, 6 alignment in helium droplets, 14,15 to name just a few developments. In addition to the various practical applications of A&O in molecular sciences, including, but not limited to rotational coherence spectroscopy (which can be used to determine accurate rotational constants 22–25 ), chemical reaction control, isotope and photofragment separation, and molecule trapping, the appearance of attochemistry 26–28 has stimulated renewed interest in A&O dynamics. Since molecular rotations typically proceed on a picosecond to nanosecond timescale, efficient rotational A&O allows for carrying out femtosecond or attosecond dynamics experiments in a molecule‐fixed frame, providing potentially much richer information than experiments carried out on isotropic samples 29–31 .…”

“…Different A&O realizations have been proposed and demonstrated, 1 , 2 , 3 , 4 such as adiabatic 5 , 6 , 7 , 8 and non‐adiabatic A&O, 9 , 10 , 11 , 12 , 13 A&O along one, 11 , 14 , 15 two, 6 or three dimensions, 16 , 17 , 18 , 19 using linearly 10 , 11 , 14 or circularly 15 polarized pulses, employing single 14 , 15 or multiple pulses, 9 , 10 , 16 , 18 utilizing optical 10 , 14 , 16 and/or terahertz (THz) 10 , 20 , 21 pulses, optical centrifuges, 6 alignment in helium droplets, 14 , 15 to name just a few developments. In addition to the various practical applications of A&O in molecular sciences, including, but not limited to rotational coherence spectroscopy (which can be used to determine accurate rotational constants 22 , 23 , 24 , 25 ), chemical reaction control, isotope and photofragment separation, and molecule trapping, the appearance of attochemistry 26 , 27 , 28 has stimulated renewed interest in A&O dynamics. Since molecular rotations typically pr...…”