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A new excited−state spectroscopic method is reported. It is a two−color laser−induced grating tecnique for detecting optical transitions of rovibronically excited molecules in the gas phase. (AIP)

A high‐resolution directly recording grating spectrometer has been used to measure the line breadths of absorption lines in both the P and R branches of the 002 band of HCN. The observed line breadths, corrected for Doppler and instrument broadening, indicate that the earliest classical theory of Lindholm predicts the correct J dependence of pressure broadening between J=0 and J=25. The observed pressure broadening appears to be sensibly independent of J for J=27 to J=34. Hence the lines fail to become extremely narrow as J gets large, the line narrowing being a phenomenon required by existing theories which consider only J‐dependent terms. The high J half‐width, 0.0055 cm—1/cm Hg, is nearly equal to the term which must be added to Lindholm's earliest classical expression to bring it into agreement with observations at the band maximum. Present measurements agree well with the J=0 to J=1 microwave measurement by Smith et al. and also with the uncorrected line breadths measured at 580 mm Hg by Lindholm.

The far‐infrared spectra of dimethylsulfide, isobutylene, and acetone in the 240–10‐cm−1 spectral region are reported. Absorption bands were found at 185.5, 183.5, 180.9, 176.8, 173.0, 168.2, and 162.3 cm−1 for dimethylsulfide. For isobutylene bands were found at 214.0, 197.3, 196.3, 186.5, 181.8, 176.0, and 165.0 cm−1. The strongest bands observed for acetone were at 124.5 and 104.5 cm−1. In addition to these bands strong absorption in the 45–10‐cm−1 region was found for all three compounds.

The polarized infrared spectra of Rochelle salt from 4550 cm—1 to 8100 cm—1 have been observed with a grating spectrometer. These spectra and the Raman spectra reported by other authors have been partially interpreted. Tentative conclusions concerning the location of the hydrogen atoms in the crystal at a temperature of 300°K are drawn from the analysis of the spectra.

The near infrared spectra of N214O16 and N15N14O16 have been investigated using a high‐resolution grating spectrometer. The α's and hence the Be values for both isotopic species have been determined. From the Be values, the equilibrium N–N and N–O internuclear distances have been found to be 1.126A and 1.186A, respectively.

The pure rotation spectra of HCl, DCl, HBr, and NH3 in the region from 40 to 140 microns as measured with an automatic‐recording grating spectrometer are presented in tabular and graphical form. A photograph of a recorded spectrogram provides an indication of the quality of the data. A comparison of the experimental results with figures based on accepted values of the molecular constants shows substantial agreement.

The polarized infrared absorption spectrum of crystalline lithium hydroxide in the region between 2500 cm—1 and 8000 cm—1 has been obtained with a grating spectrometer. The spectrum consists in part of a strong band at 3678 cm—1 polarized parallel to the c axis and bracketed in a nearly symmetric manner by five pairs of side bands polarized perpendicular to the c axis and by two pairs of side bands polarized parallel to the c axis. In addition an isolated band at 7172 cm—1 is observed polarized parallel to the c axis. Changes in the spectrum as the sample temperature is increased from room temperature to 400°C are described.The hydrogen positions in lithium hydroxide have been deduced. It is shown, using the factor group selection rules as a guide, that the spectrum can be explained as consisting of an infrared active OH stretching fundamental surrounded by binary combinations of lattice fundamentals with the infrared and Raman OH fundamentals. The band at 7172 cm—1 is assigned as the binary combination o...

The fundamental vibration‐rotation band of N15O has been examined with a grating spectrometer. The molecular constants obtained are in good agreement with existing data and the isotope relations.

A high‐resolution infrared grating spectrometer has been used to investigate l‐type doubling of energy levels of the linear molecules C2H2 and HCN. Resolving power of 145 000 was obtained at 4100 cm—1 which permitted the resolution of the Q branch of ν1+ν51(Σg+→πu) of C2H2 to J″ = 6. The difference between the B′—B″ value determined from the Q branch and the same quantity obtained from the P and R branches of this band yields a value of q = 4.72×10—3 cm—1. The doublet structure in the difference band 0110→0112(π→π) of HCN has been resolved for J″≥6 in the R branch and J″≥10 in the P branch. This π→π band is treated as two bands with slightly different molecular constants. Evaluation of rotational constants shows that different α values are obtained for the + and — components of these π states. The difference in frequency between lines of equal J″ in the 000→002 and 0110→0112 bands is shown to be a quadratic function of J″. The value obtained for q′ was 7.68×10—3 cm—1.

By the use of a grating spectrometer, the infra‐red absorption spectra of aqueous solutions of five inorganic materials (KI, CuBr2, ZnBr2, CdCl2·2H2O, and NaOH) and six organic materials (acetone, CH3COONa, CH3COONH4, cane sugar, C6H5OH, and C2H5OH) were observed in the region of the water band at 4.72μ. The organic materials investigated caused a displacement of the position of maximum absorption to shorter wave‐lengths; the inorganic materials apparently caused a shift to longer wave‐lengths, but the actual effect on the water band may be masked by other absorption bands in the same region. The concentration‐shift relationship was investigated for some of the materials. Size of the solute molecule and the positive ion seemed to be of comparatively little importance.

A vacuum grating spectrometer was used to measure the absolute line strength of the vibration‐rotation fundamental of GeHy. (AIP)