Strong ortho/para effects in the vibrational spectrum of Cl−(H2)

Abstract

The predissociation spectrum of the Cl−35(H2) complex is measured between 450 and 800 cm−1 in a multipole radiofrequency ion trap at different temperatures using the FELIX infrared free electron laser. Above a certain temperature, the removal of the Cl−(p-H2) para nuclear spin isomer by ligand exchange to the Cl−(o-H2) ortho isomer is suppressed effectively, thereby making it possible to detect the spectrum of this more weakly bound complex. At trap temperatures of 30.5 and 41.5 K, we detect two vibrational bands of Cl−(p-H2) at 510(1) and 606(1) cm−1. Using accurate quantum calculations, these bands are assigned to transitions to the inter-monomer vibrational modes (v1,v2l2) = (0, 20) and (1, 20), respectively.

Vibrational Predissociation Spectra of C2N− and C3N−: Bending and Stretching Vibrations

“…The first two features might thus include an H 2 contribution. The corresponding overtones were detected at 773 cm −1 for CN − (H 2 ) [42] and at 755 cm −1 for CI − (H 2 ) [41] . In this case, the last band detected at 800(1) cm −1 can tentatively be assigned to the hindered rotation of the H 2 in combination with an H 2 intermolecular stretching vibration, similar to CI − (H 2 ).…”

“…The corresponding overtones were detected at 773 cm À 1 for CN À (H 2 ) [42] and at 755 cm À 1 for CI À (H 2 ). [41] In this case, the last band detected at 800(1) cm À 1 can tentatively be assigned to the hindered rotation of the H 2 in combination with an H 2 intermolecular stretching vibration, similar to CI À (H 2 ). Alternatively, the peak at 735(1) cm À 1 could consist or contain the combination of ν 4 + ν 5 predicted to be at 738 cm À 1 , even though the calculation predicts a vanishing intensity (see Table S2).…”

“…The advent of cryogenic multipole radio‐frequency ion traps and buffer‐gas cooling has contributed to investigate weakly‐bound ionic complexes by IRPD spectroscopy [34–39] . Here, we extend our studies on CI − (H 2 ) [40,41] and CI − (H 2 ) [42] and present the vibrational spectra of dihydrogen polycyanides C n N − (H 2 ), $${n = 2}$$ and 3 using the same experimental approach, i. e., cryogenic infrared predissociation spectroscopy. Two stable conformers (C 2 N − (H 2 ) or (H 2 )C 2 N − and C 3 N − (H 2 ) or (H 2 )C 3 N − , respectively) can be formed.…”

Vibrational spectroscopy of Cu+(H2)4: about anharmonicity and fluxionality

“…Note, the nuclear spin isomers resulting from ortho-and para-dihydrogen were recently reported to play an important role in the formation and the far-IR spectroscopy of Cl À -(H 2 ) and CN À -(H 2 ) anion complexes. 21,22,57 However, the present study focuses on the near-IR spectral region and the positions of rovibrational lines from corresponding nuclear spin isomers are expected to differ by only 0.5 cm À1 , i.e., much smaller than the bandwidth of the IR laser pulses of B3.5 cm À1 .…”

“…19,20 The rotationally-resolved IRPD spectra indicate that all these cationic complexes adopt a C 2v T-shaped M + –(H 2 ) geometry rather than the linear M + –H–H structure that is preferred in the corresponding anion complexes. 20–23 The H–H stretching frequencies are red-shifted by 67 cm −1 (Na + –H 2 ) to 406 cm −1 (Ag + –H 2 ) relative to the frequency of a free H 2 molecule (4161 cm −1 ). 24 The extent of the redshift depends on the charge and orbital interactions, which determine the balance between σ donation and π backdonation.…”