High-resolution infrared spectroscopy of supersonically cooled singlet carbenes: Bromomethylene (HCBr) in the CH stretch region
Journal Article
·
· Journal of Chemical Physics
- Univ. of Colorado, Boulder, CO (United States); National Inst. of Standards and Technology (NIST), Boulder, CO (United States); JILA/Department of Chemistry
- Cold Quanta, Boulder, CO (United States)
- Univ. of Colorado, Boulder, CO (United States); National Inst. of Standards and Technology (NIST), Boulder, CO (United States)
First high-resolution spectra of cold (~35 K) singlet bromomethylene HCBr in the CH stretching (v1) region from 2770 to 2850 cm-1 are reported using near quantum shot-noise limited laser absorption methods in a slit jet supersonic discharge expansion source. Three rovibrational bands are identified at high S/N (20:1 - 40:1) and rotationally assigned to i) the CH stretch fundamental (v1) band $$\tilde{X}$$(1,0,0) ← $$\tilde{X}$$ (0,0,0) and ii) vibrational hot bands ($$\tilde{X}$$(1,1,0) ← $$\tilde{X}$$(0,1,0) and $$\tilde{X}$$(1,0,1) ← $$\tilde{X}$$(0,0,1)) arising from vibrationally excited HCBr populated in the discharge with single quanta in either the H–C–Br bend (v2) or C–Br stretch (v3) modes. Precision rotational constants are reported for a total of six states, with an experimentally determined CH stretch vibrational frequency (2799.38 cm-1) in good agreement with previous low-resolution fluorescence studies. Detailed analysis of the fundamental v1 band highlights the presence of perturbations in the $$\tilde{X}$$(1,0,0) level, which we tentatively attribute to arise from the nearby triplet state $$\tilde{a}$$(0,0,1) through spin-orbit interaction or the multiple quanta $$\tilde{X}$$(0,2,1) singlet state via c-type Coriolis coupling. Reduced-Doppler resolution (60 MHz) in the slit-jet IR spectrometer permits clear observation of nuclear spin hyperfine structure, with experimental line shapes well reproduced by nuclear quadrupole/spin-rotation coupling constants from microwave studies. Lastly, the a-type to b-type transition intensity ratio for the fundamental CH stretch band is notably larger than predicted by a bond-dipole model, which from high level ab initio quantum calculations (CCSD(T)/PVQZ) can be attributed to vibrationally induced “charge-sloshing” of electron density along the polar C–Br bond.
- Research Organization:
- University of Colorado, Boulder, CO (United States)
- Sponsoring Organization:
- National Science Foundation (NSF); USDOE
- Contributing Organization:
- NSF(CHE, PHYS)
- Grant/Contract Number:
- SC0002123
- OSTI ID:
- 1924524
- Alternate ID(s):
- OSTI ID: 1838207
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 1 Vol. 156; ISSN 0021-9606
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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