Intramolecular vibrational energy redistribution in HCCCH₂X (X = Cl, Br, I) measured by femtosecond pump–probe experiments in a hollow waveguide

Abstract

From the analysis of high resolution overtone spectra it is well established that intramolecular vibrational energy redistribution (IVR) from an initially excited CH-stretching vibration is strongly influenced by its chemical environment. Due to a pronounced Fermi resonance between the CH-stretching and CH-bending vibrations a vibrational energy redistribution on the subpicosecond time scale (∼100 fs) is found for alkyl (sp3) CH-chromophores, whereas this doorway for energy flow is blocked for the acetylenic (sp) CH-stretching vibration because of the much lower CH-bending frequency. From the analysis of the high resolution spectra lifetimes for the initial CH-vibrational excitation of 10-100 ps or longer have been derived. In the present work we have investigated the IVR process for HCCCH2Br, HCCCH2Cl, and HCCCH2I after excitation of the first overtone of the CH-stretching vibration of the CH2X- and the CCH-group by time resolved femtosecond pump-probe experiments in a hollow waveguide. For HCCCH2Br and HCCCH2Cl a clearly different IVR behavior was found for the two different chemical environments. For the excitation of the alkyl CH-chromophore very fast initial relaxation times were found together with a slower relaxation process with τ2 = 15-40 ps, whereas for the acetylenic CH-stretching vibration a relaxation time τ3 = 70-200 ps has been determined. For HCCCH2I also for the excitation of the CCH-group a relatively fast relaxation process with a time constant τ2 = 6 ps could be identified which might result from a not yet identified strong vibrational coupling between the excited first overtone of the acetylenic CH-stretching vibrations with a combination state including the CI-stretching vibration.

Wide‐Range Color‐Tunable Organic Phosphorescence Materials for Printable and Writable Security Inks

“…Thef ast relaxation lifetime,w ithin 2ps ( Figure S12), are heavily distorted by nonlinear effects arising from the temporal overlap of the pump and probe pulse,a t the first several picoseconds of our decay signal. [14] All the guest molecules exhibit the similar vibrational lifetimes ranging from 120 to 170 ps,w hereas the vibrational lifetime of the TPAs is only 62 ps,w hich is significantly shorter than those of the guest molecules ( Figure S12). Since the maximum absorption wavelength red shifts from 321 nm to 407 nm from FDA to NDBA ( Figure S8a), and DQD shows the maximum molar absorption coefficient at 370 nm, DQD possesses the highest excitation efficiency.…”

High resolution FTIR and diode laser spectroscopy of trifluoromethylacetylene and tetrafluoromethane in a supersonic jet expansion

“…The complete rotational vibrational line analysis of high resolution infrared spectra of polyatomic molecules is of of gas sensing [8], as well as a benchmark for ab initio theory [9][10][11][12] or fundamental investigations of the primary processes of intramolecular quantum dynamics and kinetics [13][14][15][16][17][18][19][20][21]. In this context the combination of high resolution spectroscopic techniques with molecular beams from supersonic jet expansions has played an important role, as the cooling to low effective rotational and vibrational temperatures as well as the reduction of the Doppler width greatly simplifies the analysis of the complex spectra [13,.…”

Mode‐Selective Vibrational‐Tunneling Dynamics in theN=2 Triad of the Hydrogen‐Bonded (HF)2Cluster

“…The highly nonstatistical nature of hydrogen bond dissociation in (HFHF) cluster is obviously related to a strong, nonstatistical inhibition of intramolecular vibrational energy flow as one of the increasing number of examples of the nonstatistical nature of intramolecular vibrational redistribution in polyatomic systems (see Refs. [47,[107][108][109][110][111], for example, and refs cited therein). However, the infrared multiphoton excitation of the large, covalently bound cluster C 60 leading to the early observation of vibrational preionization to give rise to the ionic cluster C 60 + and its further fragmentation appeared to be largely statistical.…”