Edge effects in chirped-pulse Fourier transform microwave spectra

Abstract

Recent applications of chirped-pulse Fourier transform microwave and millimeter wave spectroscopy have motivated the use of short (10-50 ns) chirped excitation pulses. In this regime, individual transitions within the chirped pulse bandwidth do not all, in effect, experience the same frequency sweep through resonance from far above to far below (or vice versa), and "edge effects" may dominate the relative intensities. We analyze this effect and provide simplifying expressions for the linear fast passage polarization response in the limit of long and short excitation pulses. In the long pulse limit, the polarization response converges to a rectangular function of frequency, and in the short pulse limit, the polarization response morphs into a form proportional to the window function of the Fourier-transform-limited excitation pulse.

High-Resolution Gas Phase Spectroscopy of Molecules Desorbed from an Ice Surface: A Proof-of-Principle Study

“…However, first, the intensity of the microwave power should be calibrated. To do this, a number of effects, such as chirped pulse duration, 35 edge effects, 36 sideband gains, and frequency-and temperature-dependent losses in the waveguide, have to be taken into account. This task was out of the borders of the study presented here.…”

Photodissociation transition states characterized by chirped pulse millimeter wave spectroscopy

“…The relative intensities of the excitation chirp between the 68.7 ← 78.7 GHz and 84.4 → 97.0 GHz chirping regions for DCN, DNC, and HCN, HNC were independently verified to be comparable by referencing them to a T rot = 6 ± 1 K PGOPHER (92) simulation of the parent CH 2 CDCN transitions. No adjustment of intensities for the chirp direction(34) was made since the spectral regions of interest are significantly smaller than the chirp ranges(93). Data for the HCN plot from ref 38…”

Time-Resolved Kinetic Chirped-Pulse Rotational Spectroscopy in a Room-Temperature Flow Reactor

“…The two-sided arrow emphasizes the equal role of these levels . In the weak-field excitation limit, ,, in an optically thin sample, and in the absence of the chirp edge effects, has the following dependence ,− Here, k is the Boltzmann constant, E J ′ and E J ″ are the rotational energies of the J ′ and J ″ levels, ω is the mm-wave transition frequency, x S J ′ J ″ is the transition strength, μ x is the projection of the electric dipole moment, n is the number density, and L is the length of the reactor. Note that the M -degeneracy of the J levels is included in x S J ′ J ″ .…”

“…The two-sided arrow emphasizes the equal role of these levels. 62 In the weak-field excitation limit, 31,32,63 in an optically thin sample, 64 and in the absence of the chirp edge effects, 65 ′ ↔ ″ S v J J ( , ) has the following dependence 24,66−69…”